By Mike Mount, CNN
One of the worst-kept secrets in Washington is that Defense Secretary Leon Panetta will soon leave his post for a calmer life at his beloved Northern California ranch.
Panetta and those close to him have given no public indication he will leave upon the start of the next Obama administration, but people close to the defense secretary say Panetta is more than ready to retire from his long public service life.
Four choices to replace Panetta seem to be getting the most buzz as the announcement day gets closer.
Security Clearance talked to people inside the Department of Defense, on Capitol Hill and in the defense community about what each potential nominee could bring to the table, and what issues might work against them being chosen by the president for the top job.
Here are profiles:
In 2009 when she started at the Pentagon, she held one of the most powerful positions in the building as the under decretary of defense for policy. Considered the number-three position in the Department of Defense under the secretary and the deputy secretary, she was the highest-ranking woman in the building and advised then-Secretary Robert Gates, who was followed by Panetta, on everything from the formulation of national security and defense policy to as oversight of military plans and operations.
When she was tapped for the position, conventional wisdom and hallway buzz, had her being groomed for the top job in the Pentagon upon the eventual departure of Gates.
But Flournoy left the Pentagon a year ago saying she had to start spending time with her family of a husband and three young children.
Those who know Flournoy, including two Pentagon officials who have worked with her, say that may not be entirely accurate, and point to what she actually did in her off time - becoming a senior adviser on Obama's last campaign and spending time at the defense-oriented think tank she co-founded.
The result? Her name popped back up a serious contender for the top Pentagon job.
She has the pedigree for it, with degrees from Harvard and Oxford, and a strong background in defense academia and defense policy analysis. She would bring a sharp and critical mind to the position with the ability to see the small and big picture of how the military should operate post-Iraq and Afghanistan.
Sen. John Kerry
If the president wants more of a diplomat, a steady hand and somebody who can offer restraint in the face of flexing combat muscle, then the Massachusetts senator could get the nod.
A Vietnam veteran who was awarded three Purple Hearts, Kerry is no stranger to the military. But most of his political career has been dealing with foreign policy - some say that is a benefit when heading up a war department. Kerry has also made strong connections in Pakistan which could be beneficial as the U.S. begins to wind the war down in Afghanistan.
"This administration will be facing possible conflict with Iran and a build up of Chinese influence around Asia, and (to have) somebody who can offer some restraint and slow down the drums of military force, Kerry would be a good choice in that aspect," said Michael O'Hanlon, of the Brookings Institution.
Kerry, a Democrat and former presidential candidate, is also well regarded by both Democrats and Republicans, a major plus for a job that involves plenty of lobbying of Congress. Though he offers a steady hand and can keep the trains running, some say he probably won't be bringing any new big ideas to the job,
Some say his nomination would be a consolation prize to the job he reportedly really wants, that of secretary of state. Some in uniform chuckle at the thought of Kerry walking the halls of the E-ring peering out the window over the Potomac toward the home of the State Department at Washington's Foggy Bottom.
But as a senator, Kerry may not have the management depth needed for the day-to-day operations in the Pentagon some see as crucial for the job. The White House would have to ensure a good number two was at the helm to ensure success of a Secretary of Defense Kerry.
A decorated Vietnam veteran and a staunch supporter of the military, former Republican Sen. Chuck Hagel has positioned himself to stay in military circles. He was senator from Nebraska from 1997 to 2009, and as a senator was a member of the Foreign Relations and Intelligence committees.
Now the head of the Atlantic Council - a NATO and military -oriented think tank - he is considered an independent thinker and a choice to please Republicans.
However, his stance on Iraq could get him in trouble with Republicans. Hagel blasted the Bush White House, likening the war in Iraq to that of Vietnam, and he later said the Iraq surge was the most dangerous foreign policy "blunder" since Vietnam. That could be a problem for the most senior Republican on Senate Armed Services, John McCain of Arizona, who was a major force behind pushing for the surge.
The White House, responsible for closing the war in Iraq, may not want to start dragging all of that history back up. There is some additional bad blood between the two as Hagel, a fellow Republican senator, did not endorse McCain during his 2008 presidential bid.
He is also seen by many Republicans as being anti-Israel and has called for direct negotiations with Iran's leadership. A lot of baggage to carry around in Washington these days.
But it's that attitude that also might attract Hagel to Obama. Somebody who can show restraint on flexing combat muscle and using the DoD post as more of a diplomatic post as the United States starts facing new challenges outside of the war in Afghanistan.
Some say Hagel getting this current buzz close even as the White House is expected to name its new national security team is surprising, saying his independent streak might be a deterrent.
Once a leading contender in Washington buzz, but now thought to be out of the running by many inside defense circles, the current number two at the Pentagon is a classic manager the Defense Department needs to “keep the trains running,” as one former Defense official puts it.
There is also some talk of him being chosen to head up the Department of Energy.
“The number two job needs somebody who takes care of the business side of the Pentagon operations, and Carter fits that bill well.”
But Carter’s problem could be that he lacks the full experience to be Secretary of Defense right now as the White House looks for a smooth transition out of Afghanistan.
Prior to this role, he headed weapons procurement as the under secretary for acquisition, technology and logistics from April 2009 to October 2011. In that role, Carter was most noted for accelerating the urgent need for vehicles that protected troops from roadside bombs in Iraq, at the order of then-Secretary Robert Gates.
Carter is considered a top defense-oriented academic mind with stints at Harvard’s Kennedy school and as co-director of the Preventive Defense Project. In the Clinton administration, he was an assistant secretary at the Pentagon for international security policy. Some liken his leadership thinking to William Cohen, one of President Bill Clinton's defense secretaries who focused on internal operations rather than global perspectives.
Carter could still be a strong candidate, but it would depend on what kind of Pentagon President Obama is looking for.
With upcoming budget cuts and shifting focus away from the last two wars, Obama will need somebody to guide that change in Pentagon thinking. Carter could fit that bill.