President Obama officially announced Thursday the shuffling of his senior national security team, naming a quartet of diplomatic, intelligence and defense officials to help manage the final stage of two wars, a tumultuous Middle East and a politically charged debate over the federal budget that will touch all agencies.

In an East Room ceremony, Obama called his four nominees — Leon E. Panetta as Defense secretary; Lt. Gen. John R. Allen as commander of international forces in Afghanistan; Gen. David H. Petraeus as director of the Central Intelligence Agency; and Ryan C. Crocker as ambassador to Afghanistan — as “leaders of enormous integrity and talent who have devoted their lives to keeping our nation strong and secure.”

The nominees, all deeply experienced either on the battlefield or in the ways of Washington, leave largely intact a national security team that has been criticized as insular and often lacking in creative thinking, particularly at a time of historic change in the Middle East and North Africa. The only new member of the team is Crocker, a five-time ambassador whom Obama coaxed from a comfortable retirement in academia.

Still, Obama, noting the “urgent challenges” facing the country, signaled that he is seeking continuity at a “pivotal period.”

“I felt it was absolutely critical that we had this team in place so that we can stay focused on our missions, maintain our momentum, and keep our nation secure,” Obama said. “I cannot think of a group of individuals better suited to lead our national security team during this difficult time.”

The nominees will take their posts over the next five months if confirmed by the Senate, an often politically fraught process that each man has successfully navigated in the past. Even before Obama officially announced the nominees, Senate leaders praised the selections and signaled a quick confirmation process ahead, as the president called for in his remarks.

In a statement released shortly after Obama’s announcement, Senate Republican Leader Mitch McConnell (Ky.) said “the president is to be commended for choosing competence and continuity in” nominating Petraeus and Panetta to new posts.

“I have valued working with both of these leaders,” he said.

Sen. John F. Kerry (Mass.), the Democratic chairman of the Senate Foreign Relations Committee, said that “while the country will miss the service of [Defense] Secretary [Robert M.] Gates, Leon Panetta and General Petraeus are first-rate public servants whose reputations and records transcend party, and I expect broad approval and swift confirmations.”

Kerry said he also “looked forward to an early confirmation hearing” on Crocker’s nomination.

Obama, in thanking Gates, who in addition to managing two wars also identified deep budget cuts at the Pentagon at the president’s direction, said, “I’m confident Bob Gates will be remembered as one of the finest Defense secretaries in American history.”

He said he was “equally confident” that Panetta, the current CIA director tapped to succeed Gates, would carry on his predecessor’s “reform agenda.”

Panetta is a former chairman of the House Budget Committee and was director of the Office of Management and Budget during the Clinton administration. He indicated that part of his mission at the Pentagon would be to trim spending where necessary without endangering national security.

“Today we are a nation at war, and job one will be to ensure that we remain the strongest military power in the world,” Panetta said.

“Yet this is also a time for hard choice choices,” he continued. “It’s about ensuring that we are able to prevail in the conflicts in which we are now engaged. But it’s also about being able to be strong and disciplined in applying our nation’s limited resources to defending America.”

Petraeus, the current commander of international forces in Afghanistan, said he is leaving the post “with a sense of guarded optimism about the trajectory of the mission.”

Obama will begin bringing home U.S. forces from Afghanistan this summer, and the debate over how quickly to do so will occupy the new national security team.

Petraeus praised Obama’s selection of Allen, the Marine lieutenant general who is currently deputy chief of the Central Command, and Crocker, whom he worked with as commander in Iraq during the 2007 “surge” that helped change the course of the war.

Crocker will be replacing Karl W. Eikenberry, the former general who has often been at odds with the military over Afghanistan policy, as ambassador to Kabul.

“The challenges are formidable and the stakes are high,” Crocker, who re-opened the U.S. Embassy in Kabul after the 2001 invasion, said of his new post. “9/11 came to us out of Afghanistan. Our enemy must never again have that opportunity.”