The expected departure of Chief of Staff Rahm Emanuel to run for mayor of Chicago is likely to mark the beginning of a wider White House shake-up, officials said Wednesday, one aimed at helping the administration regain its footing in the aftermath of anticipated Democratic losses in the midterm elections and positioning President Obama for a tough 2012 reelection fight.

Such a reorganization is not unusual at this point in a presidency and particularly in a White House such as Obama's, which has been running full out for two years - grappling with two wars, a financial crisis and an ambitious policy agenda. Many of its key players have begun to let it be known that they are burned out and looking for an exit or a new role.

The stresses have also exposed weaknesses in a White House operation that many in Washington have come to regard as too insular.

Especially for those who also were involved in Obama's two-year campaign, "this is sort of the end of year four, not necessarily the end of year two," press secretary Robert Gibbs told reporters traveling Wednesday with Obama. "So I think there's no doubt that there will be people that return to their lives and their families."

"But we've got a while before that," he added. "We've got about two months before this election before we get to a lot of those decisions."

Those will indeed be busy months, not only because of the election but because of the press of business at the end of the congressional session.

Obama, however, may not have the luxury of waiting before beginning to decide how he wants to reshape the White House operation for the second half of his term.

Chicago Mayor Richard M. Daley's announcement Tuesday that he will retire "came out of the blue," said one official, who agreed to speak about internal deliberations only on the condition of anonymity.

Emanuel, given the chance to make a bid for the job that he has long said is a dream, now must decide quickly whether to jump into the race, for which the filing deadline is Nov. 22. And that means Obama and his team could have to begin confronting some very specific choices of their own.

The chief of staff is not the only top official whose days at the White House appear to be numbered. Also expected to leave at some point after the elections is chief political strategist David Axelrod.

He has made no secret of his desire to return to his family in Chicago. But another imperative for Axelrod may be the need to get the Obama reelection operation up and running, particularly if the president's political standing is damaged after the midterms.

There are also likely to be changes in the communications operation. Officials expect that Gibbs, whose relations with the White House press corps have been contentious, will want to give up the briefing-room podium in favor of a role that would put him behind the scenes as a presidential counselor.