President Obama has opted for continuity in a major reshuffle of his national security team, choosing familiar names to help him complete the U.S. withdrawal from Iraq, define the endgame in Afghanistan and give the Pentagon its fair share of budget cuts.

Three of the four nominees Obama plans to announce Thursday — CIA Director Leon Panetta to be secretary of defense; the Afghanistan commander, Gen. David H. Petraeus, to head the CIA; and Central Command’s deputy chief, Lt. Gen. John R. Allen, to take over in Afghanistan — have been deeply involved in formulating administration strategy in the tumultuous Middle East and South Asia.

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.

Crocker’s nomination, the administration official said, will be sent to the Senate immediately.

Lawmakers ‘pleased’

As news of Obama’s planned announcement emerged Wednesday, lawmakers of both parties were broadly approving. “The sum total of these picks is that the President has chosen experienced people with unique capabilities to serve our nation at a dangerous time,” Sen. Lindsey O. Graham (R-S.C.) said in a statement. “I could not be more pleased.”

Gates, who is highly respected on Capitol Hill, made his own calls to key lawmakers Wednesday to emphasize that Panetta is his recommended successor and that support for Allen is unanimous among the Pentagon’s civilian and military leaders. Allen also worked closely with Thomas E. Donilon, Obama’s national security adviser, when Donilon headed the National Security Council’s powerful deputies committee. Petraeus was also touted by Gates.

Obama’s status quo choices come at a time of rising concern about the nation’s fiscal health and appear designed to manage the end of the wars, rather than to rethink the way they are fought or consider how the United States might take advantage of wrenching political changes in the Middle East.

With public concern rising on domestic issues, the last thing the administration needs on the eve of a reelection effort are signs of internal discord or looming failure in expensive enterprises abroad. Already, a Washington Post-ABC News poll this week indicated that 49 percent of Americans disapprove of Obama’s management of the Afghan conflict, which he has described as a “war of necessity.”

The changes are consistent with what critics have said is Obama’s shift toward advisers he knows, rather than the team of political rivals, led by Secretary of State Hillary Rodham Clinton, he initially brought to his Cabinet. Clinton has said she would not serve in a second Obama term, and Obama, despite his lack of foreign policy experience, has increasingly become his own chief theoretician.

Although Panetta has received high marks for his management of the CIA, he is more a political than a policy animal and can be trusted to protect Obama’s interests as the 2012 election approaches.

Reluctant nominees

Like Crocker, Panetta reluctantly agreed to his nomination only after a personal appeal from Obama; he committed to the job in a meeting with the president Monday. Obama had two private White House meetings with Petraeus last month.

Panetta and Petraeus were reportedly on opposite sides of the Afghanistan-Pakistan debate during the White House’s policy review in late 2009, with the CIA chief — along with Gates and Vice President Biden — expressing doubt about Petraeus’s plans to implement the kind of expensive, troop-heavy counterinsurgency strategy that succeeded in Iraq.

But Petraeus and other advocates of the strategy won Obama’s vote in exchange for assurances that a withdrawal could begin this summer.

Since then, the general has worked to tone down a public persona that tended to set White House sensitivities on edge, while claiming welcomed progress in the Afghan war. Petraeus has said the planned drawdown of U.S. forces will begin as scheduled this summer.

The senior administration official declined to comment on any past differences on Afghanistan and emphasized that the policy currently moving forward is well in place, with a gradual turnover of security duties to the Afghan military and police and a final withdrawal of U.S., NATO and other coalition combat forces by the end of 2014.

“This is the strategy signed on to by the NATO partners” under Petraeus’s command in Afghanistan, and “the strategy Petraeus has been implementing,” the official said. “It will be implemented by General Allen” and Crocker, he said.

Crocker, as a senior State Department official during the first administration of George W. Bush, reopened the U.S. Embassy in Afghanistan after the fall of the Taliban. Karzai, in a call to Washington on Wednesday morning, has already signed off on Crocker’s ambassadorship, the official said.

Staff writer Scott Wilson contributed to this report.