"The sheer improbability of this victory is part of what makes D-Day so memorable," Mr. Obama said.
He spoke under a sunny sky at the American Cemetery on cliffs overlooking Omaha Beach and the rest of the Normandy coastline where on June 6, 1944 Allied ships disgorged American, British and Canadian soldiers under the withering fire of Nazi troops awaiting the Allies' cross-channel gamble.
Arriving by helicopter, President Obama visited an American battlefield museum with his wife, Michelle; laid a wreath in honor of the fallen; greeted U.S. military members; and mingled with uniformed World War II veterans.
Normandy's cliffs, still pocked with gun emplacements and other reminders of the war, including the white headstones of thousands of fallen American troops, provided sure footing for a new U.S. commander in chief who has made an early priority of strengthening America's relations with Europe.
Mr. Obama noted that Normandy has been visited by many U.S. presidents and predicted, "Long after our time on this Earth has passed, one word will still bring forth the pride and awe of men and women who will never meet the heroes who sit before us: D-Day."
He said the lessons of that pivotal effort are eternal.
"Friends and veterans, what we cannot forget - what we must not forget - is that D-Day was a time and a place where the bravery and selflessness of a few was able to change the course of an entire century," he said.
One American veteran of the D-Day landings, Ralph K. Manley, 85, stood among the graves at the American cemetery and marveled at the thousands of visitors. Manley, who lost a twin brother in the war and was a parachute infantryman with the 101st Airborne Division at Normandy, told a reporter that the importance of the commemoration went beyond Mr. Obama's presence.
"I can see President Obama on the television when I'm home," he said. "But I could never see all the respect and courtesy that all these people pay to come here this day. That's the part that feels really heartwarming, the one that makes me feel good about the sacrifices we made. I'm so thankful I'm not one of those tombstones right here."
Speaking at Omaha Beach at a time when he is directing wars in Iraq and Afghanistan - both of which have lasted longer than the U.S. involvement in World War II - President Obama described in stark terms the harsh conditions the Allied invaders faced at Normandy. He noted that in many ways the seaborne invasion plan went awry, leaving the assaulting forces vulnerable to Nazi guns in their path.
"When the ships landed here at Omaha, an unimaginable hell rained down on the men inside," he said. "Many never made it out of the boats."
Some 215,000 Allied soldiers, and roughly as many Germans, were killed or wounded during D-Day and the ensuing nearly three months it took to secure the Allied capture of Normandy, a battle that helped free France from Nazi control.
Mr. Obama paid tribute to the Allies - the British, the Canadian, the French as well as the Russians, "who sustained some of the war's heaviest casualties on the Eastern front."
"At an hour of maximum danger, amid the bleakest of circumstances, men who thought themselves ordinary found it within themselves to do the extraordinary," he said. "They fought out of a simple sense of duty - a duty sustained by the same ideals for which their countrymen had fought and bled for over two centuries."
Earlier, Sarkozy, Canadian Prime Minister Stephen Harper and British Prime Minister Gordon Brown each recalled the sacrifices of the Allies.
Mr. Obama noted that his grandfather, Stanley Dunham, arrived at Normandy six weeks after D-Day and marched across France in Lt. Gen. George S. Patton's army. Attending with Mr. Obama was his great uncle, Charles Payne, who was part of the first American division to reach and liberate a Nazi concentration camp that the president and his great uncle visited in Germany on Friday.
Mr. Obama saluted the contributions of individual veterans of the Normandy landings, including one veteran, Jim Norene, who fought as a member of the 101st Airborne Division.
"Last night, after visiting this cemetery for one last time, he passed away in his sleep," the president said. "Jim was gravely ill when he left his home, and he knew that he might not return. But just as he did 65 years ago, he came anyway. May he now rest in peace with the boys he once bled with, and may his family always find solace in the heroism he showed here."
Bilateral Meeting Presented United Front
Before the ceremony, Mr. Obama met in nearby Caen with Sarkozy. In an exchange with reporters, the president indicated that he was considering stronger responses to what he called North Korean provocations.
Mr. Obama said he preferred to stick to a diplomatic approach to North Korea, after its nuclear and ballistic missile tests, but said that would work only if the communist nation was willing to engage in serious talks. He made no mention of a military option, but suggested he sees a limit to the effectiveness of diplomacy.
"I don't think there should be an assumption that we will simply continue down a path in which North Korea is constantly destabilizing the region and we continue to act in the same ways," he said.
The two stood united in efforts to thwart Iran's disputed nuclear ambitions and bring about a Mideast peace that provides for separate Israeli and Palestinian states.
"We want peace. We want dialogue. We want to help them develop. But we do not want military nuclear weapons to spread and we are clear on that," Sarkozy said of Iran, adding that he worries about "insane statements" by Iranian President Mahmoud Ahmadinejad. He called anew for Iran not to develop a nuclear weapons program.
Mr. Obama, in turn, reaffirmed that there must be "tough diplomacy" with Tehran on this issue.
Sarkozy also agreed with President Obama's call for Israel to stop building settlements in the West Bank, and Mr. Obama said that he and Sarkozy will work "in close collaboration" on many issues, including anti-terrorism strategy.(AP Photo/Thierry Charlier)
First lady Michelle Obama, French first lady Carla Bruni-Sarkozy, French President Nicolas Sarkozy and President Barack Obama are seen during an arrival ceremony at the Prefecture of Caen, France on Saturday, June 6, 2009.
The French leader said his country would take some detainees currently held at the Guantanamo Bay, Cuba, facility, as the United States has asked.
France has resisted U.S. appeals for greater efforts to stimulate European economies and more European troops in Afghanistan, where the United States has stepped up its engagement under Obama's administration.
CBS News correspondent Chip Reid reports that after today's ceremony, the president and first lady will head back to Paris, where they'll meet up with their daughters for a very brief weekend in the City of Lights.
Michelle Obama and her two daughters paid a surprise visit to the Eiffel Tower on Friday night. It is the first excursion abroad as presidential daughters for 10-year-old Malia and 7-year-old Sasha, expected to stay in France until at least Monday. The president leaves tomorrow.