Secretary of Defense Robert Gates will be departing soon. He won’t leave before the July 2011 deadline that the president set for commencement of troop withdrawals in Afghanistan. But he will go this year. Conservatives have been dismayed by his comments on Iraq and on Libya, but he has worked to defend the Pentagon from the White House budget axe. Now a list of successors has been floated:

Obama administration officials are considering Central Intelligence Agency director Leon Panetta, Democratic Senator Jack Reed of Rhode Island and Navy Secretary Ray Mabus as possible replacements for Defense Secretary Robert Gates, according to an administration official.

Michele Flournoy, undersecretary of defense for policy, is also among the candidates being looked at to succeed Gates, who previously has said that he plans to retire sometime this year, according to the official, who spoke on condition of anonymity to talk about the selection process.

Reed subsequently denied he would be the pick.

The list, to the dismay of conservative hawks, does not include Sen. Joe Lieberman (I-Conn.), who was a long shot at best but would have been a bold advocate in the war against Islamic terror. But, alas, it seems he would have been too bold for this president. Also missing is former Sen. Chuck Hagel, whose selection would have reinforced concerns about the president’s stance toward Israel and his disinclination to use hard power.

As for the others, the buzz from the Pentagon is that Flournoy is, quite bluntly, a diversity pick. A defense expert tells me, “She’s respected, but no one in the building thinks she’s ready for the top job.”

As for Panetta, he battled with the Justice Department, and largely lost, on a range of issues concerning anti-terror tactics and re-investigation of CIA officials previously cleared for use of enhanced interrogation techniques. “Panetta knows how to play the D.C. game and seems to have done a good job at the Agency; but running that fiefdom, which is more about personal relations and skills, is a way different job than managing the Pentagon,” says a former White House adviser and defense staffer. And while Mabus holds the post of Navy Secretary, that job is less than meets the eye. That same source observes, “These days being a service secretary is not what it was, say, during the Reagan years when John Lehman was Secretary of Navy. You really control very little and spend most of your time being a kind of PR speaker for your service.”

But it is far from clear that any of these choices — or anyone else — will be able to perform what is now the essential function of Obama’s defense secretary, namely being the grown up in an otherwise overwhelmed and inept national security team and fighting against cuts to the defense budget at a time when the president is actually expanding our military obligations. Candidly, anyone who is up for the job is likely someone Obama wouldn’t want.