WASHINGTON » When President Barack Obama assembled his first national security team, it was quickly dubbed, not always accurately, the “Team of Rivals.” Now that some of its key members are heading for the exits, the question is whether his next war council could be named the “Corps of Consensus.”

The departure this summer of Defense Secretary Robert M. Gates, arguably the most powerful voice in the Cabinet, leaves more than an empty seat in the Situation Room. It is a chance for Obama, at a critical moment in the wars in Iraq and Afghanistan and amid the Arab uprisings, to rethink the dynamic of the group making some of the most critical decisions in his presidency.

Not long after Gates settles into his retirement house in Washington state, the term will expire for the chairman of the Joint Chiefs of Staff, Adm. Mike Mullen, who, like the defense secretary, was appointed by President George W. Bush. And a week ago, Deputy Secretary of State James B. Steinberg announced that he was leaving for an academic job — removing one of the crucial players in Obama’s efforts to manage China’s rise.

But Gates’ role is the most critical. He often allied with Secretary of State Hillary Rodham Clinton — who has said that she intends to leave the administration when this term ends — including persuading Obama to launch the military buildup in Afghanistan in 2009. Together they won many other battles, but they visibly split last month on the military intervention in Libya.

In filling Gates’ chair, will Obama be looking for a close new partner for Clinton or a dissenter who might challenge the course that is already set?

White House officials, not surprisingly, will not say. But they acknowledge that Gates, a former director of the Central Intelligence Agency who first worked in the White House when Obama was in junior high school, is an unusual figure. Outsiders say that finding someone who replicates each of Gates’ strengths — or his willingness to disagree with the emerging policy on Libya, as he did in private discussions before Obama’s final decision — will be next to impossible.

“Gates has played a unique role,” said Brent Scowcroft, the national security adviser under President George Bush and a close friend of the secretary of defense. “And it will be very hard to replace him, not only for his stewardship at defense, but for the balanced approach he was able to bring to the foreign policy debates, the fact that he is a Republican and the fact that he worked so closely with Hillary.”

From the White House to the Pentagon, names of leading candidates are emerging, but it is unclear if any have deep support in the Oval Office.

The front-runner is clearly the CIA director, Leon E. Panetta, which could open his job for Gen. David H. Petraeus, now the commander in Afghanistan. (An argument for appointing the general, who has had a sometimes strained relationship with the president, is that it could occupy a potential outside critic with an important government job.)

An oft-discussed alternative would be moving Ray Mabus, now the secretary of the Navy, to Gates’ job; his unusual resume ranges from the Gulf of Mexico to the Persian Gulf. (He was governor of Mississippi and ambassador to Saudi Arabia.)

A more mainstream choice would be John J. Hamre, who was deputy defense secretary under President Bill Clinton, or even Colin L. Powell or Sen. Jack Reed, D-R.I. and a former Army paratrooper.

And there is also discussion about whether Gen. James E. Cartwright, the vice chairman of the Joint Chiefs and one of Obama’s favorite strategists, might be promoted to chairman despite concerns among fellow senior officers about his command and decision-making style. The “Team of Rivals” notion emerged early in Obama’s search for a national security team, a reference to the Cabinet that Lincoln assembled at the opening of the Civil War. Since Hillary Clinton competed with Obama for the Democratic presidential nomination for president, the phrase had an instant appeal, but it was never a precise fit.

There were clear camps of top advisers during the 2009 Afghanistan debate, when Gates, Mullen, Petraeus and Clinton lined up against Vice President Joseph R. Biden Jr., Rahm Emanuel, then the chief of staff, and others who advocated a much smaller buildup, focused chiefly on counterterrorism.

With a staged troop withdrawal beginning this summer, it will be up to those who succeed Gates and Mullen to manage that process, while dealing with an officers corps that is trying to slow the pace.

At the State Department, Clinton oversees the civilian side of the Afghan conflict and the difficult case of Pakistan, where a White House report issued earlier this week conceded there is “no clear path to defeating the insurgency.” But she is without Richard C. Holbrooke, the veteran diplomat who died in December and has been replaced by the low-key Marc Grossman, who has shunned the spotlight that Holbrooke so enjoyed.

One of the critical questions is whether Clinton, who won the argument on an intervention with Libya, will see her influence expand when Gates leaves — or whether her success will depend on once again teaming up with the new defense secretary.

“You get the impression that she is taking a larger role,” said Sen. John McCain, the Arizona Republican who ran against Obama in 2008. “We had a classified briefing the other day on Libya with both Gates and Clinton, and Hillary did 90 percent of the talking.” (That may have been partly because Gates had already made it clear that he had reservations about entering the Libyan conflict.)

Thomas E. Donilon, who became national security adviser last fall, could prove influential in some personnel choices. An experienced manager, he appears to have a far closer relationship to Obama than did his predecessor, Gen. James L. Jones.

Donilon is viewed as a fan of Cartwright, long considered a leading candidate for chairman of the Joint Chiefs. Cartwright’s reputation is based on his expertise in complex, high-technology issues, like missile defense and cyberwar, that appeal to the president.

But there are other contenders — Adm. James G. Stavridis, Gen. Martin E. Dempsey, Gen. Ray Odierno and Gen. Norton A. Schwartz among them — and Obama’s final choice for chairman will be particularly telling.

For his next chairman, Obama has a choice between an independent-minded general or one who represents the military establishment. During the Afghanistan-Pakistan policymaking debate, Cartwright was said to have voiced concerns about a large commitment of additional troops to Afghanistan — a view that aligned him more with Biden than with Gates or Mullen.

Coupled with an official inquiry into his command and disciplinary decisions involving a female subordinate — Cartwright was cleared of all wrongdoing — some senior officers express concern about his leadership style and management decisions.