Obama's Pentagon Team: Who's the Next Secretary of Defense When Robert Gates Leaves?

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Is Leon Panetta headed to the Pentagon to succeed Defense Secretary Bob Gates when he retires later this year?

Will Gen. David Petraeus leave the war in Afghanistan to take over Panetta's post at the CIA if Panetta takes over at the Pentagon?

If Petraeus doesn't go to the CIA, will he succeed Adm. Mike Mullen as Chairman of the Joint Chiefs of Staff when his term runs out?

These are all questions that national security types in Washington have been discussing this week while the rest of the city has been consumed by the possibility of a government shutdown.

But the real question is: Are any of these possibilities grounded in fact?

The only certainty is that there will be a new top leadership team at the Pentagon later this year when Defense Secretary Robert Gates and Joint Chiefs Chairman Adm. Mike Mullen step down from their posts.

Gates has said on multiple occasions that he intends to retire from his post later this year, though he has never said exactly when he would do so.

Just yesterday in Baghdad, he told a group of American soldiers that he was likely on his last trip to Iraq as Secretary of Defense. Having made quarterly visits to Iraq in recent years, he lent some credence to speculation that he could step down this summer following the start of the U.S. drawdown in Afghanistan scheduled for July.

Mullen's second two-year term as chairman of the Joint Chiefs will run out on October 1. Mullen's successor would likely have to be named by the White House in early summer to allow enough time for the Senate confirmation process.

Leon Panetta's name surfaced in recent weeks as a potential Gates successor, but Washington was abuzz this week with the possibility that Gen. David Petraeus could replace Panetta if he does head to the Pentagon.

Defense Secretary Robert Gates, left, and Adm. Mike Mullen at a 2008 hearing.

A U.S. official tells ABC News there are White House discussions about having Petraeus take over at the CIA. But that possibility would only be contingent on an opening at the CIA if Panetta were to move on.

But CIA spokesman George Little says about the Panetta talk, "He isn't seeking any other job and hasn't been asked by the President to take on a different role." He added, "Director Panetta is proud to lead the men and women of the CIA and is focused squarely on the agency's mission."

While Panetta has garnered all the recent attention, others seen as potential contenders to succeed Gates are Navy Secretary Ray Mabus, Defense Under Secretary for Policy Michele Flournoy and former Deputy Defense Secretary John Hamre. Secretary of State Hillary Clinton ended speculation she was in the running when she told reporters last month that she intended to remain at her post and then leave the administration after the 2012 election.

Pentagon Shakeup: Who Will Run Defense Department?

Conventional wisdom has Gen. James Cartwright, Vice Chairman of the Joint Chiefs of Staff, as the leading candidate to succeed Mullen, who will have served four years as the President's top military advisor. His profile became higher after Bob Woodward, in his book "Obama's Wars," labeled him as "Obama's favorite general."

But Gen. Petraeus has also been discussed as a potential successor to Mullen since it was first reported that he is scheduled to step down later this year as the top commander of NATO forces in Afghanistan.

It's unclear when Petraeus would leave his post, but a Defense official says he has "pledged to see this through another fighting season if that was necessary."

But with few four-star openings available to Petraeus if he remains in the military, the possibility that he could take over at the CIA seemed an intriguing choice to many in Washington.

A Defense official says such talk is just "premature."

Marine Lt. Gen. John Allen, the current number two officer at U.S. Central Command, is seen as the likely candidate to succeed Petraeus as the top NATO commander in Afghanistan.