President Bush vowed today that the United States would meet its "responsibility to history" and wipe out terrorism.
He told the mourners that a "unity against terror is now extending across the world."
"This nation is peaceful but fierce when stirred to anger," the president said at a prayer service beneath the soaring ceiling of Washington National Cathedral.
"This conflict was begun in timing and terms of others. It will end in a way and at an hour of our choosing."
Mr Bush spoke in a city on edge - and to a nation in mourning for the loss of an estimated 5,000 people who perished in attacks on Tuesday at the World Trade Centre in New York and the Pentagon outside Washington.
"We will read all these names and linger over them and learn their stories, and many Americans will weep," the president said.
Mr Bush addressed the nationally televised service on a day he declared should be marked by prayer and remembrance.
But there was business to attend to, as well.
Tonight Mr Bush arrived New York tonight to survey the carnage of Tuesday's attacks on the World Trade Centre.
Security was tight as the President met rescue and emergency workers at the scene of the disaster where the twin towers of the World Trade Centre once stood.
He was flown to a New Jersey air base in the presidential plane Air Force One this evening.