WASHINGTON — Some of President Barack Obama’s top national security advisers believed late last year that they had reached consensus on an aspect of Afghanistan strategy after meeting with Gen. James L. Jones, the national security adviser.

They should have checked first with Denis McDonough, the National Security Council’s chief of staff. "I don’t think that’s where the president is on that," McDonough informed his higher-ups, according to two administration officials.

A couple of months later, when state officials in Florida tried to halt medical evacuation flights from Haiti, McDonough, on the ground in earthquake-stunned Port-au-Prince, got on his BlackBerry, which is never far from his side. Within a few hours, as other officials tell it, Homeland Security Secretary Janet Napolitano acted to keep the airspace open.

Forget Secretary of State Hillary Rodham Clinton or Defense Secretary Robert M. Gates. When it comes to national security, Obama’s inner circle is so tight it largely consists of McDonough, a 40-year-old from Minnesota who is unknown to most Americans but who is so close to the president that his colleagues — including his superiors — often will not make a move on big issues without checking with him first.

"He is the keeper of the president’s flame," said Cheryl Mills, Clinton’s chief of staff. Brian Katulis, a foreign policy expert who is a good friend of McDonough, said, "When the president needs to pick up the phone and call someone on national security, that someone is Denis."

When Obama got word of the "Rolling Stone" article that would lead to his firing of Gen. Stanley A. McChrystal as the top commander in Afghanistan, he immediately summoned three people to the Oval Office: Rahm Emanuel, his chief of staff; David Axelrod, his adviser of longest standing, and McDonough. Not until later did the president consult the rest of the national security team.

McDonough is intensively protective of the president, and is well known for picking up the phone — or his BlackBerry — to take people to task, from reporters to Washington talking heads to other Obama officials who go off message. He once spent the entirety of his bike ride home to Takoma Park, Md., from the White House late one recent night arguing on the cell phone with a reporter who he believed had mischaracterized an internal administration debate over Iraq policy.

He has berated some of the Democratic Party’s most distinguished foreign policy dignitaries when they have dared to critique Obama publicly, leaving a miffed Washington establishment in his wake muttering — off the record, of course — about just who this guy thinks he is.

His e-mail messages are legendary across Washington, and usually appear right after a critique hits the Web. When David Rothkopf, a national security expert and Commerce Department official in the Clinton administration, wrote a column for The Washington Post last August that praised Clinton — and notably, not Obama — as overseeing "profound changes" to American foreign policy, the first e-mail message Rothkopf received came from you-know-who.

"Interesting choice for a profile," McDonough wrote.

"Political figures like to have people who are watching their back," Rothkopf said in an interview. "I understand why people are bugged by McDonough; they’re jealous of his access to the president. But the president deserves to have someone like him."

McDonough declined to be interviewed for this article.

Obama arrived in Washington six years ago as a political outsider, a Chicago novice with no historical ties to the Democratic foreign policy establishment. Early on in the presidential campaign, McDonough signed up with Obama.

A foreign policy adviser to Sen. Tom Daschle before Daschle’s 2004 election defeat, McDonough was then at the Center for American Progress, a liberal research organization.

He was all over the country for Obama during the campaign. McDonough shoveled the driveway and sidewalk for a Davenport, Iowa, couple as part of an unsuccessful effort to woo them into caucusing for Obama instead of Clinton. He spent so much time canvassing his assigned precinct that by the night of the Iowa caucuses he was greeting most of the caucus-goers by name, prompting his colleagues to start calling him the town mayor. (Obama won five of the seven delegates in the precinct.)

McDonough looks more like a "Town & Country" cover model than a Washington foreign policy wonk. At 6 foot 3, he weighs himself regularly in the White House doctor’s office to make sure he does not go above 200 pounds.

But early on during the campaign, McDonough took on the role of Obama’s foreign policy guru. "Foreign policy was always the high wire for us on the campaign," one administration official said. Obama, he said, "trusted Denis to get the job done but not sand down his views."

After the Democratic debate in South Carolina in 2007, when Obama termed "ridiculous" the notion of not talking to America’s enemies, McDonough and Obama mulled the ensuing furor in the candidate’s bare Massachusetts Avenue campaign office. McDonough, according to a former campaign official, "told the president, ‘You have nothing to walk back on your position. You don’t need lectures on foreign policy from the Democratic foreign policy establishment."’

The bond they forged during the campaign sealed McDonough’s role as Obama’s most trusted foreign policy aide in the White House. Today, many of the old Democratic rivals are in the Obama cabinet, deciding Afghanistan, Iraq and Iran policy. And McDonough is far closer to the president than they are.

At both the Pentagon and the State Department, officials report being chewed out by McDonough when he believes they have leaked something before the White House is ready. In recent months, McDonough has mellowed, his colleagues say. In fact, he began 2010 telling reporters that he was going to make an effort to be nice, and now routinely mentions that he will not blow up during his almost nightly phone calls to dispute articles.

At the White House, McDonough presses the East Wing to make sure that junior members of the National Security Council staff are invited to receptions and parties.

In an interview, Jones said he could not recall when McDonough told him and other officials that their evolving consensus on Afghanistan policy was not where Obama wanted to go. But "as a generic anecdote, I’m not bothered by that; it’s what I expect him to do," he said.

"It’s a big asset for all of us to have Denis, who has known the president for so long," Jones said. "He knows how he thinks about issues."