Psst: Did you hear who may replace Bob Gates?

As President Barack Obama prepares to defend his military intervention in Libya in a speech at National Defense University Monday night, he is set to lose his cabinet's most important national security heavyweight, holdover Defense Secretary Robert Gates.

In recent farewell visits to Russia, Bahrain, Egypt and Israel, as well as at congressional hearings and Sunday news show appearances, Gates has made little secret of his plans to leave the job in the coming months--Defense officials anticipate a summer departure--nor of his concerns about the United States embarking on another military intervention in the Middle East.

Here, for instance, was a candid Gates on NBC's "Meet the Press" Sunday, when asked about Libya:

"No, I don't think it's a vital interest for the United States, but we clearly have interests there, and it's a part of the region which is a vital interest for the United States," he told host David Gregory, as Secretary of State Hillary Clinton, appearing with him, rushed to explain the strategic rationale for U.S. military engagement in Libya.

The former CIA director's straight-shooting echoed his earlier skepticism of calls for a Libya no-fly zone. "Let's call a spade a spade: A no-fly zone begins with an attack on Libya to destroy the air defenses," Gates said at a congressional hearing earlier this month. "It's a big operation in a big country."

While several reporters and commentators have remarked upon the veteran bureaucratic operator's striking candor as he heads for the exit, the Obama White House has bigger worries than Gates straying off message. Namely: who can they get to replace him? Who has the combination of national security credentials, juice with both sides of the aisle in Congress, international prestige, and management skills to run one of the biggest organizations in the world? And of that small pool, with whom does the White House enjoy a solid enough rapport to entrust with the responsibility?

Several officials tell The Envoy that the Obama administration is likely to name CIA Director Leon Panetta to succeed Gates as Secretary of Defense.

Officials say Panetta has emerged as the most likely nominee from a field of candidates that has reportedly included Under Secretary of Defense for Policy Michele Flournoy, Sen. Jack Reed (D-RI), former Deputy Defense Secretary John Hamre, former Nebraska Sen. Chuck Hagel, and former Secretary of State and chairman of the Joint Chiefs of Staff Colin Powell, a somtimes Obama confidante.

Like Gates, Panetta has served as CIA director. The former California Democratic lawmaker and former Clinton White House chief of staff is widely considered to have done a terrific job winning the loyalty of the legendarily mistrustful CIA. He mostly kept the CIA from being a White House headache, has strong ties with both Republicans and Democrats in Congress, and has quietly traveled around the world developing solid relationships with world leaders, including in the Middle East, officials say.

Panetta for the post "makes sense," said a former Defense Department official who asked for anonymity discussing personnel issues. "He has strong, good credentials on both sides of aisle … He's managed things before and has done a good job at CIA." Panetta, if nominated and confirmed, would also be the first Democrat to hold the position since Bill Perry in 1997.

"From the beginning, Panetta had enormous credibility with the White House," said a former senior U.S. official who helped advise the Obama campaign. Noting that Panetta also served as White House chief of staff and head of the Office of Management and Budget, the former official said Panetta has a "terrific record in Congress and did an extraordinary job from the moment he was appointed [as CIA Director] in developing the confidence of the Agency."

Referencing Panetta's fierce public defense of CIA personnel--including in fights early in Obama's term with then House speaker Nancy Pelosi (D-Ca.), who claimed she was not briefed on CIA waterboarding -- he "showed he was prepared to stand up for them in serious ways while working quietly internally to clean up a lot of the messes in the agency that existed from the previous administration," the former senior U.S. official said. "He redeveloped [the CIA's] credibility, both within the U.S. government as well as with foreign governments."

Panetta also successfully battled Obama's first director of National Intelligence Dennis Blair, the former official noted, to protect "traditional Agency funding and authorities," including on the decision of who--CIA director or DNI--gets to pick the top U.S. intelligence official posted in countries around the world. "Panetta is one of the smartest people in Washington," the former official continued. "He will be able to work with them and work them."

Indeed, the main drawback to nominating Panetta for the job, according to this source, is it opens up the can of worms of who should replace him as CIA director.

On that question, the rumors are hazier. One name that's been suggested is former Sen. Chuck Hagel (R-Neb.), currently the chairman of Obama's President Intelligence Advisory Board, who, said the former senior official, "knows Obama quite well." As a moderate Republican, Hagel may also "help with bipartisanship," the former official said.

A CIA spokesman declined to comment on the personnel rumors. Gates' spokesman also declined to comment.

(Defense Secretary Robert Gates, left, and CIA Director Leon Panetta, right, walk into the East Room of the White House in Washington, Tuesday, Sept. 21, 2010: Pablo Martinez Monsivais/AP)