"Today we honor the men and women who have worn the nation's uniform and were last seen on duty for the battles of Iraq and Afghanistan," Bush said. "Today, we recall that liberty is always the achievement of courage and today we remember all who have died, all who are still missing and all who mourn."
Bush was joined by his wife, first lady Laura Bush, Secretary of Defense Donald H. Rumsfeld and Gen. Richard Myers, chairman of the Joint Chiefs of Staff, for the annual memorial rite under overcast skies.
"All of the good people we honor today were willing to die in the service of their country and the service of their cause," he said. "May God keep us ever grateful."
Bush paid tribute particularly to those lost in the battle to oust Iraq's Saddam Hussein — a war that has caused roughly 160 U.S. casualties but which has now moved into a stabilization and reconstruction phase.
Bush, accompanied by Rumsfeld, earlier walked to the site of the Tomb of the Unknowns, turned and faced the monument, placing his right hand over his heart and listened to the somber playing of Taps. He then laid a wreath at the tomb, continuing a Memorial Day presidential tradition.
Rumsfeld, speaking before Bush, said, "Today, we face new threats to our freedom. They will be met with the same courage and the same commitment and like the foes of times past, they too will be defeated."
Said Myers: "As we remember these brave Americans, we recall that the achievements of those who preceded us secured the liberty that we enjoy today."
Myers called the gravesites at Arlington National Cemetery "eternal reminders of honor and sacrifice."
Bush and his wife returned earlier from a long weekend at their home in Crawford, Texas. Monday's holiday observance included a White House reception for military families.
In a Memorial Day declaration earlier, the president gave a special salute to "the men and women in our nation's armed forces who are working with our coalition partners to restore civil order, provide critical humanitarian aid, and renew Afghanistan and Iraq."
"Americans stand with the families who grieve, and we share in their great sorrow and great pride," he said. "There will be no homecoming on this earth for those lost in battle, but we know that this reunion will one day come."