The American-French ceremony at Omaha Beach began a day of 70th anniversary D-Day commemorations along the French coast once held by Nazis.
The ceremony featured the solemn traditions of military memorials.
Obama and French President Francois Hollande — who also spoke — placed a wreath at a colonnade near the gravesites. They held their hands over their hearts as a bugler played taps and jets roared overhead. A 21-gun salute boomed over the thousands of stone crosses at Omaha Beach.
Related: Photos of D-Day, then and now
The American and French leaders could also be seen chatting amiably with elderly veterans who visited under much different circumstances seven decades ago.
Obama will lunch with nearly two dozen other world leaders in attendance, including the 88-year-old Queen Elizabeth II of Great Britain. Another guest: Russian President Vladimir Putin, who has been feuding with Obama over Russia's incursion into Ukraine.
An international commemoration is planned for the afternoon at another D-Day landing point, Sword Beach.
At Omaha Beach, Obama told the stories of average Americans who fought their way into Normandy on June 6, 1944, many of whom attended the ceremony in their slightly bigger dress uniforms.
He spoke of Wilson Cowell, who, told he couldn't pilot airplanes during World War II because he lacked a college degree, decided to become a parachutist instead -- at age 16.
"Rock" Merritt, who also parachuted into Normandy on that deadly morning, still spends time talking to today's service members at Fort Bragg, Obama said.
And Harry Kulkowitz, the son of Russian immigrants, lied about his age to get into the service.
"Don't worry, Harry," Obama said. "The statute of limitations has expired."
Of these soldiers, Obama said: "Whenever the world makes you cynical, stop and think of these men."
The president also cited his grandfather, who fought with George Patton's army, and grandmother, who helped build the "mighty arsenal of democracy" back home.
D-Day veterans can be comforted to know that their tradition is being carried by "the 9/11 Generation" that fought bravely in Afghanistan, Iraq, and elsewhere, Obama said.
In addition to those who fought, Obama praised the massive machinery that bolstered the D-Day invasion -- some 5,000 ships and landing craft, about 11,000 planes,and 30,000 vehicles, the largest armada in history.
"If prayer were made of sound, the skies over England that night would have defended the world," Obama said.
Some of the bloodiest fighting took place there at Omaha Beach, Obama said, as "blood soaked the water (and) bombs broke the sky ... 'Hell's Beach' had earned its name."
As night fell on June 6, 1944, despite deaths and strategic setbacks, the Americans had claimed Omaha Beach.
"Within a week," Obama said, "the world's bloodiest beach had become the world's busiest port. Within a month, 1 million Allied troops thundered through Normandy into Europe."