Gates, the Defense secretary who has served since late 2006, told Foreign Policy magazine that he would likely retire in 2011.

"I think that it would be a mistake to wait until January 2012," Gates said in an interview published on Monday. "This is not the kind of job you want to fill in the spring of an election year."

The Defense secretary took office almost four years ago under Republican President George W. Bush, and was the only member of Bush's Cabinet asked to stay on in his position by President Obama.

The White House said this afternoon that President Obama was grateful for Gates's service, though they were unsurprised to see him leave.

“The president is gratefully thankful for that service, but any announcement will come from him,” White House Deputy Press Secretary Bill Burton told a pool reporter. “It’s not a surprise to see him discussing his plans to move on.”

Replacing Gates would be difficult, as the secretary has credibility with lawmakers on both sides of the aisle.

Obama has looked to Gates as one of his top military advisers since taking office, and sided with the Defense secretary, Secretary of State Hillary ClintonHillary Diane Rodham ClintonClinton backs Georgia governor hopeful on eve of primary Pressure rising on GOP after Trump–DOJ fight’s latest turn Press: Why Trump should thank FBI MORE and others in his administration on last year's decision to send a "surge" of troops to Afghanistan.

"We'll have completed the surge. We'll have done the assessment in December," Gates said. "And it seems like somewhere there in 2011 is a logical opportunity to hand off."

Gates noted that if he were to stay around much longer, he will have spent more time on the job than most previous people to hold the position.

"If I stay until January 2011 ... I will have been in the job longer than all but four of my predecessors. And those four are Robert McNamara, Don Rumsfeld, Cap Weinberger and Charles E. Wilson," he said. 

Updated 1:06 p.m.