Mr. Bush, joined by Gen. Richard Myers, chairman of the Joint Chiefs of Staff, and Defense Secretary Donald H. Rumsfeld, laid a wreath at the Tomb of the Unknowns at Arlington National Cemetery. First lady Laura Bush also attended.
After laying the wreath near the tomb, which holds the unidentified remains of U.S. soldiers who fought and died in several wars, the president led the nation in remembering those who paid the ultimate price in service to the country.
In his remarks, he made passing reference to ongoing conflicts involving the United States and the thousands of troops serving there.
"We have seen the character of the men and women who wear our country's uniform in places like Kabul and Kandahar, in Mosul and Baghdad. We have seen their decency and their brave spirit," Mr. Bush told a rain-sprinkled crowd of several hundred.
"Because of their fierce courage America is safer. Two terror regimes are gone forever and more than 50 million souls now live in freedom," he said.
Earlier Monday, President Bush's Democratic rival, John Kerry, paid a solemn visit to the Vietnam Veterans Memorial across the river from Arlington Cemetery. Kerry walked with the family of William Bronson of Gardner, Mass., who died in 1976 from a seizure related to a head wound suffered in 1968 during combat in Vietnam.
Kerry, a Vietnam veteran, came home from the war with three Purple Hearts and Silver and Bronze stars, and soon became a leader of the anti-war movement.
President Bush received an enthusiastic welcome from the crowd at a critical phase in the war in Iraq. Unrest there continues and political control is to pass to an interim Iraqi government on June 30.
A year ago on Memorial Day, Mr. Bush's potential political problems stemming from the Iraq war were just becoming apparent.
The U.S. government confidently predicted that weapons of mass destruction would be found and American generals said troops were in the process of stabilizing Iraq.
No such weapons have been found.
The president had declared four weeks before Memorial Day 2003 that major combat operations had ended and his approval ratings were well over 60 percent in most polls; now they are in the 40s, the lowest of his presidency.
A year ago at this time, more than 160 American soldiers had been killed in Iraq. The total since has risen to more than 800, and last week the Pentagon reported that the number wounded in action is approaching 4,700.
Meanwhile, the scent of charcoal and sunblock mingled with the smell of car exhaust over the holiday weekend as Americans marked the official start of summer by firing up barbecues and taking to the beach — and hitting the highways to get there.
On the national mall, a long-sought World War II memorial officially opened on Saturday.
Hundreds of thousands of people attended Saturday's ceremony, including President Bush. Tens of thousands of World War II veterans — "the greatest generation" — were in Washington for the event.
Many Americans spent Memorial Day on the move. More than 37 million people were expected to travel more than 50 miles this weekend,
Thirty million people were expected to travel by car — more than last year, despite rising gas prices and the reported threat of terrorism.
The National Safety Council predicted that 476 people may die and 24,700 suffer disabling injuries in crashes over the weekend. But 376 people will survive crashes because of seatbelts, the NSC says — and 121 more lives might be spared if those people belted in, too.
More than 4 million people were expected to fly. The federal official in charge of the nation's airports said security had been "stepped up a notch" in the face of the renewed terror warnings, and said authorities were asking the public to be vigilant.
"If they see anything unusual, report it — an unattended package, something that just doesn't look right, even odd behavior in the terminal or on the aircraft," FAA Administrator Marion Blakey said on NBC.
She said photographs of seven suspected terrorists released Wednesday by the FBI "are everywhere" and that screeners have been redeployed to some of the busiest airports in anticipation of heavy Memorial Day holiday travel.
"Certainly we are going to be on red alert looking for those individuals," Blakey said on ABC.
Memorial Day traces its official start to May 30, 1868, when Maj. Gen. John A. Logan, the head of a Civil War veterans' organization, declared "Decoration Day."
In his proclamation, Logan said the day was "designated for the purpose of strewing with flowers, or other decorating, the graves of comrades who died in defense of their country during the late rebellion, and whose bodies now lie in almost every city, village and hamlet churchyard in the land."
"We should guard their graves with sacred vigilance," he wrote.
According to Defense Department records, more than 1 million American soldiers have died in wars, from the 4,435 killed in the Revolutionary War to the roughly 800 who have died so far in Iraq.