WASHINGTON (CNN) -- President Bush on Monday lauded U.S. troops as "an awesome bunch of people" and lamented that some of them have had to die in defense of freedom.
"In a world where freedom is constantly under attack, and in a world where our security is challenged, the joys of liberty are often purchased by the sacrifices of those who serve a cause greater than themselves," Bush said.
The president delivered his Memorial Day remarks at Arlington National Cemetery, the nation's main military cemetery, after laying a wreath at the Tomb of the Unknowns.
"I am humbled by those who made the ultimate sacrifice that allowed a free civilization to flourish," Bush said. "The soil of Arlington and other sites is filled with liberty's defenders. It is nourished by their heroism. It is watered by the silent tears of the mothers and fathers and husbands and wives and sons and daughters they left behind." Watch Bush profess his pride »
Bush paid tribute to two Navy SEALs killed this year in Iraq, both of whom are buried at the cemetery in Virginia outside Washington.
Chief Petty Officers Nathan H. Hardy and Michael E. Koch "shared a battlefield tradition," Bush said. "They would often head in the battle with American flags clutched to their chest underneath their uniform." Watch families searching for answers about their missing loved ones »
Hardy and Koch, both 29, were killed during an ambush, the president said.
"These two friends spent their last few moments on Earth together doing what they loved most: defending the United States of America," Bush said. "Today, Nathan Hardy and Mike Koch lay at rest next to each other right here on the grounds of Arlington."
According to the latest numbers from the Defense Department, 4,083 U.S. troops have died in the Iraq war and 423 in Afghanistan. Nearly 500 from the two theaters are buried at Arlington. Watch how one unit in Iraq is honoring its fallen »
Arlington is one of more than 100 cemeteries in the United States with military graves.
At least 4 million people reportedly visit the cemetery each year, with more than 290,000 people buried there. Officials say Arlington is running out of space.
Plans to expand the cemetery include seven areas where 100,000 urns can hold the ashes of service members.
CNN's Dick Uliano contributed to this report.