Who will fill Obama's Cabinet vacancies?

United States Ambassador to the United Nations Susan Rice

(CBS News) WASHINGTON - The vacancy at the CIA is one of many openings in the Obama administration: the secretaries of state, treasury and defense would all like to leave. So who's coming in?

White House officials told CBS News Tuesday that U.N. Ambassador Susan Rice is the frontrunner to replace Hillary Clinton as secretary of state, despite strong opposition from some Republicans.

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The 47-year-old U.N. ambassador is a close confidant to President Obama -- a former Rhodes scholar who served as assistant secretary of state under President Clinton.

She came under fire from Republicans for what she said five days after the attack in Benghazi, Libya that killed four Americans. On "Face the Nation," Rice said: "We do not have information at present that leads us to conclude that this was premeditated or pre-planned."

That would later prove to be untrue, though the White House insisted Rice was working off the CIA's best information at the time.

Several Republicans on the Senate foreign relations committee have suggested they might try to block her nomination. Florida's Marco Rubio was non-committal Tuesday.

"Obviously she based those comments on directives or information that she had," he said, "and it's important to know who that directive came from and what exactly that information was."

Massachusetts Senator John Kerry, the chair of the foreign relations committee, has also expressed interest in the secretary of state job. But on Tuesday, sources say he might be considered for secretary of defense instead if Leon Panetta leaves.

And John Brennan, the president's top counterterrorism advisor, has emerged as a leading candidate to fill the role that was unexpectedly vacated by David Petraeus as director of the CIA.

The news about Susan Rice's standing had all the feel of a trial balloon Tuesday as White House officials tried to determine just how entrenched this Republican opposition is and how difficult the confirmation process would be.

  • Nancy Cordes
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    Nancy Cordes is CBS News' congressional correspondent.