Being secretary of state is a grueling job; you're on the road most weeks, and often you get a lot less say in your country's foreign policy than you'd like. No wonder running the show in Foggy Bottom tends to be a four-year gig. So now that Secretary of State Hillary Clinton has said she can't imagine herself serving another four years after 2012, the obvious question becomes: Who might replace her?

Foreign-policy hands say the choice will depend on what kind of image President Obama wants to project, and what's going on in the world at the time.

"Obama's situation and the state of American foreign policy is extraordinarily fluid right now," said the Council on Foreign Relations' Walter Russell Mead. "His choice will depend on how he wants to engage the world: to kill them with kindness or to take a more aggressive approach."

Here is an initial short list, compiled with help from Cable readers and experts:

Early frontrunner: John Kerry

Kerry has been campaigning for the job since before Obama's election. He looked eminently diplomatic in convincing Afghan President Hamid Karzai to agree to a new election. And his steady stewardship of the Senate Foreign Relations Committee seems to have erased doubts about his ability to head an organization.  He's got international profile and his Massachusetts seat is (relatively?) safe.

Gray eminence: Richard Lugar

Lugar is well-respected on both sides of the aisle, has strong nonproliferation credentials, deep expertise on international issues, and has been a staunch defender of the State Department bureaucracy. His appointment would signal Obama's continued commitment to having a bipartisan cabinet. The question will be: As an 80-year-old man in 2012, has he got the vigor to do it?

Waiting in the wings: Jim Steinberg

Steinberg is said to be somewhat disappointed at not getting a higher posting in the first round of the Obama appointments, but he's been amazingly active as deputy secretary of state, injecting himself into almost every issue and taking on Asia as his personal policy domain. He knows the building, which would make for a smooth transition. His reported clashes within the department and throughout the interagency would be his only drawback.

Already in the cabinet: Susan Rice

Rice spends more time in Washington than most of her U.N. ambassador predecessors. With full cabinet rank, she's not shy in playing a role in foreign policy so far, and she benefits from her close personal relationship with Obama. Her appointment would signal a redoubling of the effort toward engagement and international diplomacy. But if times are tough and wars are raging, her chances might be slimmer.

A bridge too far:  Richard Holbrooke/George Mitchell

Either of these senior envoys would have seemed like a logical successor to Clinton a year ago. Both men are grand poobahs of the foreign policy establishment, but their respective efforts to solve major international problems have thus far met with limited success. If either the situations in Afghanistan or the Middle East were to vastly improve between now and 2012, however, their stock would go straight up.

Always the bridesmaid: Chuck Hagel

A media darling, Hagel's name is always floated when one of these opportunities come up. Fiercely independent and blunt, his style never seemed to match up with the academic intellectualism of Obama. What's more, he reportedly turned down high-level ambassadorships because he didn't want to travel, so it's doubtful he would be in serious consideration.

Dark horse: Gen. David Petraeus

When Petraeus's term as head of Central Command winds down, there will be nationwide speculation about his next role. If the international atmosphere is one of danger and uncertainty, Petraeus's stature could help him overcome concerns about having a military man be the face of American foreign policy. Obama has also shown a willingness to co-opt potential presidential rivals, and the general has been regularly mooted as a Republican contender in 2012 -- notwithstanding his vigorous disavowals of any political ambitions.

JOEL SAGET/AFP/Getty Images