French President Jacques Chirac welcomed President Bush upon his arrival at the American cemetery in Colleville-sur-Mer, where 9,387 fallen U.S. fighters are buried.
Both leaders sought to reinvigorate the U.S.-European bonds that were cemented during and after World War II.
Despite continued tensions between the United States and France over Iraq, the leaders of both nations in their speeches stressed the ties of friendship between the allies.
"France will never forget," Chirac said. "It will never forget those men who made the supreme sacrifice to liberate our soil, our native land, our continent, from the yoke of Nazi barbarity and its murderous folly. Nor will it ever forget its debt to America, its everlasting friend."
Mr. Bush, recalling "the immensity of the moment" that triggered the ultimate defeat of the Third Reich, also tried to ease the strain in the trans-Atlantic alliance.
"Our great alliance of freedom is strong, and it is still needed today," Mr. Bush said. "America would do it again for our friends."
President Bush urged world leaders to move past their differences, reports CBS News Correspondent John Roberts. His subtle, but unmistakable message being that America sacrificed to save France, now France must help save America in Iraq.
French and American flags flew at half-staff in memory of President Ronald Reagan, who died Saturday at age 93 following a 10-year battle with Alzheimer's disease.
Hollywood star Tom Hanks and director Steven Spielberg, makers of the movie about the invasion, "Saving Private Ryan," sat discreetly in the audience amid aging veterans in military uniforms and wheelchairs.
Queen Elizabeth II opened the ceremony at Juno Beach — the beach that Canadian soldiers were assigned to capture — to thank them for their sacrifices.
"Britain had been directly threatened by the enemy, but you came across the Atlantic from the relative security of your homeland to fight for the freedom of Europe," the queen said.
Several thousand people, including hundreds of British veterans, crowded between rows of white gravestones for the British-French memorial service at a British cemetery in Bayeux.
"On behalf of my generation, the younger one, I thank you," British Prime Minister Tony Blair told Australian veteran Gordon Church, 96, who landed on Gold Beach.
At dawn on Sunday, veterans proudly supporting their medals came to Omaha Beach, the bloodiest of all the five landing beaches, to remember friends who died there 60 years ago.
With more than 20 world leaders arriving in Normandy at a time of high terror threat, France deployed fighter jets, surface-to-air missiles and 15,000 gendarmes and soldiers for security. Access to the region was to be sharply restricted by police after daybreak.
Russian President Vladimir Putin was among 24 leaders expected for Sunday's main event: A pomp-filled ceremony in Arromanches, near the midpoint of the five code-named beaches where roughly 156,000 soldiers — mostly American, British and Canadian — stormed in from the English Channel on D-Day.
Later Sunday, Chirac was to decorate 16 veterans from nearly a dozen nations with the Legion of Honor, the country's most prestigious award. All told, about 300 veterans from 13 countries, mostly the United States, Britain and Canada, were to receive the Legion of Honor in ceremonies this weekend.
Some 1,300 soldiers from 14 countries are to march in parades or play national anthems with military bands. American, Belgian, British, Dutch, Norwegian and French planes are to soar overhead. Seven nations were to participate in a naval flotilla near Arromanches.
To convey the message that Europe has moved on, for the first time France has invited a German leader. Chancellor Gerhard Schroeder was to join other leaders in Arromanches and German veterans for another ceremony at one of the German cemeteries in France.
Tens of thousands of people turned out Saturday for public events to honor the sacrifices of the war veterans and fallen soldiers.
War buffs in the uniforms of U.S. paratroopers craned their necks among nearly 50,000 people for a re-enactment of D-Day jumps by American GIs near Sainte-Mere-Eglise. Families jockeyed to see Britain's Prince Charles at a wreath-laying ceremony at Pegasus Bridge in Ranville, another of the early towns liberated on D-Day.
Casualty estimates for the Allied forces vary, but range from 2,500 to more than 5,000 dead on D-Day. But one thing is clear: the waves on Normandy shores ran red with blood.
Allied soldiers scurried across heavily mined and obstacle-covered shores, while others flew into the back country in gliders or by parachute — some getting snagged in trees or buildings.
The weekend commemorations amount to one of the final honors for the aging veterans.
"I'm getting near death. I'm 82, and I'm not getting any younger," said Harry Hudec of Cleveland, Ohio, a "Red Devil" of the 508th Parachute Infantry Regiment of the U.S. 82nd Airborne Division who landed inland from Utah Beach.
Many veterans are nostalgic about fallen comrades-in-arms even as memories fade with age.
"It's gratifying that people remember," said 83-year-old James Coleman, of St. Paul, Oregon, of the 82nd's 505th Parachute Infantry Regiment. "I lost a lot of friends."