The president spoke after participating in a solemn holiday tradition, laying a wreath at the Tomb of the Unknowns at Arlington National Cemetery, the burial ground for American veterans dating to the Revolutionary War.
In brief remarks after laying the wreath and observing a moment of silence, Mr. Obama said he wondered why the country's fallen warriors felt a sense of duty and answered the call to serve, knowing they might have to make the ultimate sacrifice.
"Why in an age when so many have acted only in pursuit of narrowest self-interest have the soldiers, sailors, airmen and Marines of this generation volunteered all that they have on behalf of others," he said. "Why have they been willing to bear the heaviest burden?"
"Whatever it is, they felt some tug. They answered a call. They said 'I'll go.' That is why they are the best of America," Mr. Obama said. "That is what separates them from those who have not served in uniform, their extraordinary willingness to risk their lives for people they never met."
The president also sought to dodge a racial controversy the of holiday, sending wreaths to a monument for Confederate soldiers and a memorial honoring more than 200,000 blacks who fought for the Union during the Civil War.
The nation's first black president continued tradition and had wreaths delivered to the Confederate Memorial at Arlington National Cemetery, the 600-acre site across the Potomac River in Virginia that once was Confederate Gen. Robert E. Lee's estate. The White House also sent a wreath to the African American Civil War Memorial in Washington's historically black U Street neighborhood.
Presidents traditionally visit Arlington to personally leave a wreath at the Tomb of the Unknowns, a marble structure with the remains of unidentified U.S. military members who died during war. Presidents then have aides deliver wreaths to other memorials or monuments, generally including the Confederate memorial.
A group of about 60 professors last week sent a petition to the White House asking Mr. Obama to avoid a memorial for Confederate military members who died during the war between the North and the South.
The White House ignored the plea. Wreaths also were left at the mast of the USS Maine and at the Spanish American War Memorial, a White House aide said.
"The Arlington Confederate Monument is a denial of the wrong committed against African-Americans by slave owners, Confederates and neo-Confederates, through the monument's denial of slavery as the cause of secession and its holding up of Confederates as heroes," the petition said. "This implies that the humanity of Africans and African-Americans is of no significance."
Among those who signed the letter is 1960s radical William Ayers, a University of Chicago education professor who helped found the radical group the Weather Underground that carried out bombings at the Pentagon and the Capitol. Republicans tried to link Mr. Obama with Ayers during the presidential campaign; the two lived in the same neighborhood and served on a charity board together.
The African American Civil War Memorial had been discussed as a compromise in recent days.
"President Obama, why not send two wreaths?" Kirk Savage, an art history professor at the University of Pittsburgh, wrote in an opinion piece in The Washington Post. "One to the Confederate Memorial in Arlington Cemetery and another to the African American Civil War Memorial in the District, which commemorates the 200,000 black soldiers who fought for liberation from slavery in the Union armed forces."
Men and women in uniform saluted the president's motorcade as it made its way into the hallowed burial ground that is Arlington. As Mr. Obama stepped to the microphone, some in the audience waved American flags.
Before the ceremony, the president had a private breakfast at the White House with people who have lost loved ones in war.
Mr. Obama and his wife, Michelle, have made veterans and military families a priority during his administration. His budget proposal includes the largest, single-year funding increase in the last three decades to revamp the Department of Veterans Affairs.