ANDREWS AIR FORCE BASE, Md. - President Obama said Monday that the meaning of Memorial Day was found in the story of ordinary Americans who become extraordinary for one simple reason: love of country.

Obama, speaking to dozens of troops at Andrews Air Force Base outside Washington after his Land of Lincoln tribute in Illinois was washed out by a storm, said the nation's fallen heroes had such a deep love of country that they willingly sacrificed their own lives to protect it.

"In this time of war, we pay special tribute to the thousands of Americans who have given their lives during the wars in Afghanistan and Iraq and who have earned their place among the greatest of generations," Obama said in the Monday evening speech.

Vice President Biden earlier made the more traditional appearance at Arlington National Cemetery on Obama's behalf, saying the country had "a sacred obligation" to make sure its troops were the best equipped and best supported in the world. "As a nation, we pause to remember them," he said. "They gave their lives fulfilling their oath to this nation and to us."

Obama had readied a similar message of gratitude for his appearance at the Abraham Lincoln National Cemetery in Elwood, Ill., and actually had taken the podium to give the address when the skies opened with a downpour and thunder, lightning, and high winds.

Under a large umbrella, Obama told thousands gathered that "a little bit of rain doesn't hurt anybody, but we don't want anybody being struck by lightning." He asked people to return to their cars for their safety, and he retreated briefly to an administration building on the cemetery's grounds. A few minutes later he boarded a bus to greet military families who had come for the event.

Before the storm hit, Obama had visited a section of headstones where two Marines awaited him. After laying a wreath, he bowed his head in a moment of silence, his hands tightly clasped. Then a lone bugler played Taps.

After leaving the cemetery, Obama met privately with families of veterans and service members living at the Fisher House in Hines, Ill. It serves as a home away from home for family members whose loved ones are getting treatment at the Veterans Affairs hospital there.

At Arlington, Biden carried out the traditional wreath-laying at the Tomb of the Unknowns. He said the country's service members were "the heart and soul and, I would say, spine of this nation." Taking part in the annual ceremony, he said, was "the greatest honor of my public life."