All have worked closely with one another and, perhaps more important, with the White House over the past two years. Senior administration officials made clear that Obama is looking for execution of decisions he has already made rather than a new direction.  It is “the strongest possible team to exercise our strategies and policies,” said an official who briefed reporters on the condition of anonymity, adding: “I stress the word ‘team.’ ”  Obama, the official said, “has laid out [the changes] in a way that we believe will provide for a seamless transition in each of these positions.”  The only newcomer to be nominated, Ryan C. Crocker, is not really a newcomer. A five-time ambassador who retired in 2009, Crocker agreed to Obama’s personal request to be ambassador to Afghanistan as the administration struggles to start political negotiations with the Taliban, even as it has expanded its military operations against the insurgents.  Crocker and Petraeus, as ambassador and military commander in Iraq from 2007 to 2009, are generally considered to have set the standard for the kind of civilian-military cooperation that the Afghanistan campaign has often lacked. In addition to helping set a political endgame in motion, the White House hopes Crocker can forge a smoother relationship with Hamid Karzai, the often testy Afghan president, than could his predecessor, Ambassador Karl W. Eikenberry.  Administration officials said Crocker is uniquely qualified to join the team after serving as ambassador to Lebanon, Kuwait and Syria, in addition to Iraq and Pakistan — a key player in the Afghanistan conflict that has been a source of ongoing difficulty for the administration.  The changes are scheduled to take place gradually over the summer. Defense Secretary Robert M. Gates will retire on June 30 and, assuming Senate confirmation, Panetta will take over on July 1, according to the senior administration briefer.  Michael J. Morell, Panetta’s CIA deputy, will become interim director until September, when Petraeus will leave Afghanistan after implementing the first phase of Obama’s promised drawdown of troops there this summer. In moving to the CIA, Petraeus will resign from the military.  Allen plans to move immediately from CENTCOM to work as a special assistant to Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, where he will gradually phase into the Afghanistan job and take over upon Petraeus’s departure.
The nomination is part of a series of national security shifts that will also place Gen. David H. Petraeus in the top CIA job, officials said.