WASHINGTON >> President Barack Obama was in a bind, and his chief of staff could not figure out how he had ended up there.

Leaders of the Roman Catholic Church were up in arms last fall over a proposal to require employers to provide health insurance that covered birth control. But caving in to the church’s demands for a broad exemption in the name of religious liberty would pit the president against a crucial constituency, women’s groups, who saw the coverage as basic preventive care.

Worried about the political and legal implications, the chief of staff, William M. Daley, reached out to the proposal’s author, Kathleen Sebelius, the health and human services secretary. How, he wondered, had the White House been put in this situation with so little presidential input? “You are way out there on a limb on this,” he recalls telling her.

“It was then made clear to me that, no, there were senior White House officials who had been involved and supported this,” said Daley, who left his post early this year.

What he did not realize was that while he was trying to put out what he considered a fire, the person fanning the flames was sitting just one flight up from him: Valerie Jarrett, the Obamas’ first friend, the proposal’s chief patron and a tenacious White House operator who would ultimately outmaneuver not only Daley but also the vice president in her effort to include the broadest possible contraception coverage in the administration’s health care overhaul.

A Chicagoan who helped Obama navigate his rise through that city’s aggressive politics, Jarrett came to Washington with no national experience. But her unmatched access to the Obamas has made her a driving force in some of the most significant domestic policy decisions of the president’s first term, her persuasive power only amplified by Obama’s insular management style.

From the first, her official job has been somewhat vague. But nearly four years on, with Obama poised to accept his party’s renomination this week, her standing is clear, to her many admirers and detractors alike. “She is the single most influential person in the Obama White House,” said one former senior White House official, who like many would speak candidly only on the condition of anonymity.

“She’s there to try to promote what she understands to be what the president wants,” the former aide said. “Ultimately the president makes his own decisions. The question that is hard to get inside of, the black box, is whether she is really influencing him or merely executing decisions he’s made. That’s like asking, ‘Is the light on in the refrigerator when the door is closed?”’

Yet if that answer remains elusive, interviews with more than two dozen former and current administration officials offer a portrait of a woman wielding a many-faceted portfolio of power.

Partly it is her ubiquity, the guiding hand in everything from who sits on the Supreme Court to who sits next to whom at state dinners, the White House staff memos peppered with “VJ thinks” or “VJ says.” When the billionaire investor Warren E. Buffett showed up for a private lunch with the president last July, the table was set for three.

Jarrett often serves as a counterweight to the more centrist Clinton veterans in the administration, reminding them and her innately cautious boss that he came to Washington to do big things. Some of his boldest moves, on women’s issues, gay rights and immigration, have been in areas she cares about most. If Karl Rove was known as George W. Bush’s political brain, Jarrett is Obama’s spine.

She is also his gatekeeper, sometimes using that power to tip the balance in internal debates. After the financial crisis, as the administration grappled with how to rein in Wall Street, Jarrett made sure that Paul A. Volcker, a former Federal Reserve chairman whose voice was being drowned out, got a meeting with the president. The result: tougher measures than the president’s top economic advisers were advocating.

And she is the president’s protector in chief, or as Treasury Secretary Timothy F. Geithner put it, the person who must be as “omniscient as possible” in spotting trouble on the way. Those whom she deems to have failed Obama tell of scolding late-night calls and her trademark accusation of betrayal: “You are hurting the president.”

But she has also steered him toward controversy, as in the contraception debate. And some of Obama’s most senior advisers worry — perhaps not entirely without jealousy — that her direct access to the president has at times led to half-baked decision making and unclear lines of authority.

Obama’s first two chiefs of staff, Rahm Emanuel and Daley, clashed with Jarrett over strategic direction and over who had greater authority to interpret and carry out the president’s wishes, several officials said.

“He’s got a real mess in the West Wing,” said one close presidential adviser. “Valerie is effectively the chief of staff, and he knows, but he doesn’t know. She’s almost like Nancy Reagan was with President Reagan, but more powerful.”

TWO WHO ‘CLICKED’

The week after the 2008 election, Obama implored Jarrett to join him at the White House. She was contemplating putting her name forward for the Senate seat he had just vacated, but she quickly put those aspirations aside.

Together they carved out her wide-ranging job description: senior adviser to the president and chief liaison to the business community, state and local governments and the political left.

“For him, I think it was more important that she be there than that she have any specific job or set of issues,” said Susan Sher, Michelle Obama’s second chief of staff and a longtime friend of Jarrett.

Jarrett declined to be quoted for this article, beyond a statement: “My role is to ensure that a wide and diverse range of perspectives are heard to inform the president’s decision making process,” she said, and to “give the president candid advice.”

Parsing the psychology of the president’s bond with Jarrett has become something of a West Wing pastime: Is she some sort of mother or sister figure to an only child whose own parents variously abandoned him?

Close friends say that in Jarrett, the introverted president simply found someone who understands what makes him tick better than most.

They met more than two decades ago, when Jarrett — a lawyer, like both Obamas — offered Michelle Obama a job in the Chicago mayor’s office.

Jarrett was a single mother who had come up the ranks of city government, the daughter of a prominent African-American family. Her grandfather, Robert Taylor, built much of Chicago’s public housing, her father was a pioneering doctor, and her mother had a Chicago street named after her for her work in early childhood education. Barack Obama was a rootless but ambitious Harvard law graduate, looking to make a political name.

At their first dinner, they talked about a “philosophy of empowerment” for the downtrodden. “That’s where we clicked,” she later told Sher, and from then on she was determined to introduce Obama, almost five years her junior, to the activists and donors he needed to move first to the Legislature and then to the U.S. Senate.

In their small social circle, Jarrett, who would go on to run a Chicago real estate company and sit on numerous civic and corporate boards, “was always seen as the adult in the room,” the one looked to for guidance, said John W. Rogers Jr., a longtime friend of both Jarrett and the president.

Replicating that role in the White House, however, has not been easy.

To some extent, Jarrett is part of a White House tradition. Bill Clinton brought along his fellow Arkansan Bruce Lindsey as his Mr. Fix-It. Bush had his Texas confidantes, Karen Hughes and Harriet Miers.

But few have had the stature — and the ability to step outside traditional White House protocol — of Jarrett. She is the only staff member who regularly follows the president home from the West Wing to the residence, a practice that has earned her the nickname “the Night Stalker.” By day, Obama is “Mr. President” to her, but in social settings, he is just “Barack.” When the Obamas take an out-of-town break, she often goes along.

After a ratings agency downgraded the nation’s debt last year, it was not the Treasury secretary at the president’s side, helping map out how to manage the market’s reaction. According to a participant in the discussion, it was Jarrett, who had joined Obama and a few close friends at Camp David for his birthday.

“There is an inherent challenge in managing anyone, this is not particular to Valerie, who is a senior adviser and part of a structure, and also close personally with the family,” said David Axelrod, the president’s chief strategist. “Obviously it’s cleaner and less complicated if everyone is discussing things at the same meetings. But it’s a manageable problem.”

Aides say she never uses her private time with the president to relitigate decisions. Even so, the White House is organized around the principle that the president’s time is an administration’s most valuable commodity, not to be spent on low-priority matters or those not fully vetted. Yet several officials say that is what happened with one of Jarrett’s pet projects, Chicago’s bid for the 2016 Olympics.

Based on her assurances that his personal appeal to the Olympic committee could clinch the deal, the president flew to Copenhagen. During the flight back, CNN reported that Chicago had not survived the first round of voting.

“There was total silence,” one official recalled. “It was a long trip home.”

Jarrett cuts an elegant figure in the West Wing, with her pixie haircut and designer clothes. Aides say she can be thoughtful in little ways that matter, enlisting the president to rally staff members after political or personal setbacks. But she can also be imperious — at one event ordering a drink from a four-star general she mistook for a waiter — and attached to the trappings of power in a way some in the White House consider unseemly for a member of the staff.

A case in point is her full-time Secret Service detail. The White House refuses to disclose the number of agents or their cost, citing security concerns. But the appearance so worried some aides that two were dispatched to urge her to give the detail up.

She listened politely, one said, but the agents stayed.

A SOMETIMES TESTY LINK

Working from a cozy office previously occupied by Rove, with a staff of nearly three dozen, Jarrett is the president’s link to the world outside the White House bubble.

Former Secretary of State Condoleezza Rice occasionally uses Jarrett, with whom she has become friendly, as an informal back channel to pass along foreign policy views, officials said.

And Bob Riley, a former Republican governor of Alabama, remembers the way Jarrett responded to his pleas for equipment to contain the BP oil spill in 2010. “Within 24 hours, what we had been told was an impossible task was done,” he said.

Often, though, Jarrett seems to be more of a lightning rod for complaints of White House insularity and a thin-skinned response to detractors.

She is widely blamed for the president’s soured relationship with the business community. (To judge by donations, Wall Street has switched its allegiance to Mitt Romney.) But Jarrett’s White House defenders say that the criticism is fundamentally misplaced and that she is merely an available target for the financial community’s anger over administration policies it dislikes. Behind the scenes, they say, Jarrett has advocated pro-business policy changes like a regular review of existing regulations.

Less well known is her testy relationship with certain elements of the president’s base.

She serves as the front door to the donors who helped elect the president, reviewing guest lists to White House parties and candidates for patronage positions. But she has snubbed some early supporters, among them the financier George Soros, ignoring his pleas for a substantive meeting on the economy with the president. The message she delivered, according to one person familiar with the exchanges, was that she felt Soros was “already on the team, and that while he might want to talk to the captain, the captain was very busy.”

Soros, who has spent tens of millions of dollars on Democratic candidates and causes, is largely sitting on the sidelines this presidential election.

With Jarrett’s unquestioning belief in the president has come a tendency to take political criticism personally, “even when it would be more useful not to,” said Marilyn Katz, a Chicago friend of both Jarrett and the president. Another friend compared her to a mother whose son can do no wrong: “Even when the neighbors call, she says, ‘No, no, that can’t be.”’

So when the executive director of the American Civil Liberties Union, Anthony Romero, publicly criticized some of the president’s antiterrorism policies, she swiftly shoved back. “Great harm has been done,” she warned in an email he shared with colleagues. “There has been a material breach of trust.”

A White House spokeswoman said Jarrett does respond aggressively when she feels that the president has been attacked.

But in an interview, Romero said that “she needs to understand that we don’t work for the White House, and our job is to criticize any president who is not doing the right thing.”

Jarrett was “livid,” one former White House official said, with members of the Congressional Black Caucus who accused the president of paying insufficient attention to the particular economic woes of blacks. When the writer and academic Cornel West joined in, calling Obama the “black mascot of Wall Street,” Jarrett’s response was “ruthless,” West said.

He recalled a phone call in which she dismissed his criticism as sour grapes for not receiving a ticket to the inauguration, and said he later heard from friends that she was putting out the word that “one, I was crazy, and two, I was un-American.”

“It was a matter of letting me know that I was, in her view, way out of line and that I needed to get in line,” he said in an interview. “I conveyed to her: ‘I’m not that kind of Negro. I’m a Jesus-loving black man who tells the truth, in the White House, in the crack house or in any other house.’ She got real quiet. It was clear that she was not used to being spoken to that way.”

DRIVING THE AGENDA

When a seat on the Supreme Court opened up just months into Obama’s term, he immediately thought of Sonia Sotomayor. It would be a historic choice, making her the first Hispanic justice. But some advisers were worried by reports about her judicial temperament. Given the tough Senate votes coming up on health care and the economy, why not go with a safer pick?

Jarrett, dismissing the reports as sexist, argued that appointing Sotomayor would send an important signal, recalled Anita Dunn, who was then the president’s communications director.

It was quintessential Valerie Jarrett, according to Dunn. It is not so much that she is Obama’s liberal id. Rather, her voice is often the one at the table reminding everyone of the president’s aspirational “first principles,” that he “didn’t just come to the White House to hold the office, but to make change,” Dunn said.

That has been particularly true when it comes to diversity and issues she considers matters of civil rights.

Gay rights advocates say they considered Jarrett their “secret weapon” in the White House on issues like repealing the military’s policy of “don’t ask, don’t tell.” And while aides said Obama found his own way toward supporting same-sex marriage, Jarrett “reinforced his instincts,” Axelrod said. This is consistent with who you are, she told the president.

On immigration, Jarrett successfully urged the president to stop deporting certain illegal residents who arrived as children. And while some of his advisers worried about the political perils of legally challenging Arizona’s tough immigration law, Jarrett argued that its central provision — requiring the police to check the immigration status of people taken into custody — amounted to racial profiling, a civil rights issue “right in the president’s wheelhouse,” recalled Pete Rouse, another senior Obama adviser. (Ultimately, the Supreme Court upheld that provision, but struck down most of the law.)

Perhaps no policy area better shows how Jarrett can drive the White House agenda than the contraception mandate. Jarrett has a fiercely loyal following among those she backed for key positions throughout government, drawn mainly from a White House women’s network she helped build and nurture. The director of the Domestic Policy Council, for instance, previously worked for her, and she counts Sebelius, the health and human services secretary, among her good friends.

Through that network, Jarrett made clear her position that a broad exemption for religious employers like hospitals and universities could leave as many as 1 million women without the benefit. Sebelius was of like mind, announcing last August that only churches themselves would get a pass.

The resulting outcry prompted Daley to confront Sebelius. (Through a spokeswoman, she said she recalled a conversation with Daley but not the particulars he described.)

Catholics, a group Obama won in 2008, make up more than a quarter of the electorate. Though most personally support birth control, Daley and Vice President Joe Biden worried about how forcing church-affiliated organizations to pay for it would play.

Moreover, they felt that the rule put important Catholic allies in the health care fight in a tough position, and potentially violated a law banning regulations that impose a substantial burden on religious expression.

Biden arranged for Cardinal Timothy M. Dolan of New York to meet with the president and express the church’s view. With the support of some of the president’s political advisers, Jarrett pushed back in her own meeting with Obama, aides said. And she signaled Sebelius to “keep fighting — I’m with you on this,” said one former official with knowledge of the matter.

But by January, even friendly voices were accusing the president of throwing “his progressive Catholic allies under the bus.” Democratic members of Congress were fielding calls from constituents who felt, in the words of one, that this was a “big blunder.” In a senior advisers meeting, the president, exasperated, ordered his senior staff to “figure it out,” one participant said.

But if some expected significant backtracking, they were mistaken. In phone calls the next week, the president outlined his compromise: The burden for the coverage would shift from employers to insurers, but women who worked for religious organizations could still avail themselves of the benefit.

“When the president called me,” said Cecile Richards, the president of Planned Parenthood, “I could practically hear Valerie’s influence.”

Today, many of the issues Jarrett championed are being replayed in the campaign. In recent ads, for instance, Romney has accused the president of using “his health care plan to declare war on religion.” The president, for his part, has accused Romney of wanting to take women “back to the 1950s.”

And Jarrett has added another role to her portfolio, traveling to swing states to campaign, sometimes at Obama’s side.

“Homestretch,” she keeps telling him.

“Homestretch?” he’ll reply.

“Yes, almost there,” she says. “We’ve just got the convention, then three debates.”

© 2012 The New York Times Company