* Clinton leaves big shoes to fill at State Department
* Front-runners emerge, but doubts remain
* Obama has surprised with "out of the box" picks before
By Andrew Quinn
WASHINGTON, Nov 7 (Reuters) - With President Barack Obama locked in for another four years at the White House, a political guessing game turned on Wednesday to another big Washington question: who will succeed Hillary Clinton as secretary of state?
Clinton, one of the most popular members of Obama's Cabinet, has said she will step down when the current presidential term concludes at the end of January.
Political analysts have been handicapping the race to succeed her for months, and usually come up with the same short list of potential successors including Democratic Senator John Kerry, U.N. Ambassador Susan Rice, and National Security advisor Tom Donilon.
But each of these front-runners has drawbacks that may put the State Department out of reach, and Obama's surprise choice of Clinton - his former Democratic presidential rival - for the job in 2008 could signal a willingness to reach out of the box to find America's next top diplomat.
"Star power is important in this position. It's very difficult to follow someone as well liked and capable as Hillary Clinton with the kind of presence she has globally," said H. Andrew Schwartz, a senior vice president at the Center for Strategic and International Studies in Washington.
"It is part of Obama's effort to repair the U.S. image abroad, and he feels that stars can get that done."
State Department spokeswoman Victoria Nuland on Wednesday reiterated her boss's plans to step down.
"She intends to see through the transition of a successor, and then she will go back to private life and enjoy some rest, and think and write," Nuland said.
The departure by Clinton - often mentioned as a potential Democratic presidential candidate in 2016 - will not be the only shakeup in Obama's core national security team.
At the Pentagon, there is intense speculation that Defense Secretary Leon Panetta will step aside in early or mid-2013, after four years running the Department of Defense and the CIA.
Candidates to replace Panetta include former Pentagon policy chief Michele Flournoy, who would be the first female defense secretary, and Ashton Carter, now Panetta's deputy.
But the State Department remains the biggest prize, and the jockeying for position is well under way.
POLITICS AND POLICY
Kerry, the 2004 Democratic presidential nominee and chairman of the powerful Senate Foreign Relations Committee, rates high on the star power chart and could be eager to try his hand at secretary of state.
A sometime diplomatic troubleshooter for the Obama administration, Kerry would bring decades of experience to face policy conundrums including the Syria crisis, the Middle East peace process and the stalemate over Iran's nuclear program.
But Kerry's well-formed opinions could work against him in job where he would be expected to follow Obama's instructions to the letter, while White House strategists may fret over potentially losing his Massachusetts seat as they count every vote in the narrowly balanced Senate.
Susan Rice, the Obama administration's current ambassador to the United Nations, faces roadblocks of her own.
Tough-minded and immersed in key issues such as Iran, Rice is widely regarded as one of Obama's most capable surrogates with a direct line into the White House.
But Rice has found herself uncomfortably in the spotlight after the deadly September attack on the U.S. mission in Benghazi, Libya, with Republican lawmakers questioning her initial description of the incident as a spontaneous outburst rather than a planned attack.
Clinton and other U.S. officials have since said that Rice's comments on television news shows were based on the information available at the time, rejecting suggestions she was sent out to mislead the public.
But lingering questions over Benghazi could make the administration reluctant to put Rice through a brutal Senate confirmation process with uncertain chances of success.
Obama's national security adviser, Tom Donilon, has flown below the radar since taking on the job in 2010 although he has been at the center of White House policy-making.
Donilon, whose career has included stints as both a government official and a Washington, D.C., lawyer, is seen as an insider who could align the State Department tightly with White House priorities for a second Obama term.
But while Donilon could be an effective manager, some analysts say he may not have the chops for the high-wattage public diplomacy that has marked Clinton's tenure.
"The reality is that very few people outside of Washington know Tom Donilon," said Damon Wilson, a former official in the National Security Council who is now executive vice president of the Atlantic Council.
"He has the president's ear and the president's confidence, and has a track record of managing crises. But the question remains does he have the gravitas to be America's diplomatic face to the world."
With questions swirling over each of the established candidates, some analysts say Obama may once again go for a surprise choice - perhaps by reaching into Republican ranks.
Former Nebraska Senator Chuck Hagel has been mentioned as a potential Obama pick, while wilder guesswork brings up names ranging from former Secretary of State Colin Powell to current CIA director General David Petraeus.
But most analysts concede that, at this point, there is little concrete to go on. "The only one who knows how this is going to play out right now is the president," Wilson said.