WASHINGTON - President Obama moved yesterday to seal an overhaul of his national security team, selecting Army Gen. Martin Dempsey as the next Joint Chiefs of Staff chairman amid protracted battle in Afghanistan, U.S. involvement in the NATO-led effort against Libya's Moammar Gadhafi and a winding down of the war in Iraq.

Obama announced a new lineup of his top military leadership group in the Rose Garden of the White House just before venturing across the Potomac to pay tribute to the nation's war dead at Arlington National Cemetery. The Memorial Day announcements had been expected, although there was no immediate indication what the leadership moves might imply for possible changes in military strategy.

Already, the president had turned, in late April, to CIA Director Leon Panetta to succeed Robert Gates as secretary of defense and chose to move Army Gen. David Petraeus from his command of the Afghanistan war effort to the United States to replace Panetta at the CIA.

Marine Gen. James Cartwright had long been rumored to be Obama's favorite, and the president singled him out for praise at the announcement. But he turned instead to Dempsey, a veteran of the Iraq war, to succeed Adm. Mike Mullen as his top military adviser, calling Dempsey "one of our nation's most respected and combat-tested generals."

The president also announced that he has chosen Navy Adm. James Winnefeld to succeed Cartwright as vice chairman of the Joint Chiefs and Army Gen. Ray Odierno as his candidate to replace Dempsey as Army chief of staff.

The nominees have to be approved by the Senate, and Obama voiced hope that that could happen in a timely fashion.

At the White House, Obama called America's servicemen and women "the best our nation has to offer, and they deserve nothing but the best in return, and that includes leaders."

Later on, Obama placed a wreath at the Tomb of the Unknowns at the venerable Arlington burial grounds. And in a speech at the Arlington amphitheater in front of a flag-draped wall, the president, who had met earlier in the day with families of troops killed in war, said: "To those of you who mourn the loss of a loved one today, my heart goes out to you.

"We remember that the blessings that we enjoy as Americans came at a dear cost," he said. "Our nation owes a debt to its fallen heroes that we cannot ever fully repay. But we can honor their sacrifice, and we must." After his remarks, Obama and his wife, Michelle, visited a section of the cemetery that is the final resting place for many veterans of the wars in Iraq and Afghanistan.

Preceding Obama at the amphitheater, Gates said that the country "must never forget" its men and women in the military.

"As I come to the end of my time in this post," Gates said, " . . . I will keep these brave patriots and their families in my heart and in my prayers."

Dempsey, who began a four-year term as Army chief of staff on April 11, will have to be confirmed by the Senate, as will Winnefeld and Odierno.

Gates said that Dempsey, Winnefeld and Odierno are excellent choices.

"They possess the right mix of intellectual heft, moral courage and strategic vision to provide sound and candid advice to the president and his national security team," Gates said. "Above all, they are proven leaders of men and women in combat operations over the past decade and are uniquely qualified to guide and shape our military institutions through the challenging times ahead.

Mullen said that the trio will give "not only their best military advice, but also the great benefit of their decades of military experience and their command in combat operations." He called Odierno a "combat-proven officer who made a real difference in Iraq."

Appearing in a nationally broadcast interview yesterday morning, Mullen was asked whether a change of guard at the Joint Chiefs meant a change of strategy in Afghanistan.

"We obviously have added these forces . . . and we've really seen progress on the security side," he replied. "We will sustain losses as we have in the last few days. . . . That said, I am confident that by the end of the year, we'll be in a much, much better position."

He said he hopes that the public understands "the depth of sacrifice" made by servicemen and women.

Mullen appeared on ABC's "Good Morning America," CBS' "The Early Show" and NBC's "Today" show.