On a clear day clouded by grief and warnings of possible new terrorist attacks, New York City, Washington, D.C, and Shanksville, Pa., led the nation in mourning the more than 3,000 people killed a year ago and in rededicating itself to the still-unfolding war on terrorism.

President Bush visited all three sites of the attacks by 19 hijackers aboard four passenger jets. During a memorial service at the Pentagon, Bush declared that although the victims of Sept. 11, 2001, "died in tragedy, they did not die in vain."

He promised there, and again in a nationally televised speech in the evening from New York, that there will be no rest for the United States until the country is safe from any possible repeat of attacks that made Americans feel more vulnerable than any time since the end of the Cold War.

"In the ruins of two towers, under a flag unfurled at the Pentagon, at the funerals of the lost," he said in his evening address from Ellis Island, "we have made a sacred promise, to ourselves and to the world: We will not relent until justice is done and our nation is secure. What our enemies have begun, we will finish."

Bush put the fight against terrorism in stark moral tones. He did not mention Saddam Hussein, but officials said he had the Iraqi leader in mind when he said, "We will not allow any terrorist or tyrant to threaten civilization with weapons of mass murder."

He will attempt today to convince reluctant United Nations allies that Saddam must be toppled, with military action if necessary.

Bush said those killed in the Sept. 11 attacks are owed not just mourning but a monument in the form of "a world of liberty and security made possible by the way America leads, and by the way Americans lead our lives."

The names of the dead, pealing bells, prayer, song and steely words of defiance echoed throughout memorial services nationwide under sunny, breezy skies that were startlingly similar to the weather of a year before.

Events were carefully coordinated to coincide with the times tragedy unfolded:

• At 8:46 a.m. EDT, when the first tower of the World Trade Center was struck, moments of silence were observed at Ground Zero in New York City and at the White House, where Bush and his wife, Laura, held hands and bowed their heads.

• At 9:03 a.m., when the second plane struck the trade center, the reading of the names of the 2,801 known World Trade Center victims paused as a bell tolled.

• At 9:37 a.m., when the plane hit the Pentagon, the Bushes led a moment of silence at the Pentagon, and Washington's subway system halted for 1 minute.

• At 9:49 a.m., when the first trade-center tower collapsed, more bells pealed in New York.

• At 10:06 a.m., when United Flight 93 smashed into a Pennsylvania field, a bell tolled in Shanksville and the reading of more names began — this time of passengers and crew members who wrested control of the jet from the hijackers and likely saved a target in Washington.

• At 10:29 a.m., when the second trade center tower collapsed, bells and sirens sounded throughout New York.

At the Pentagon service yesterday, Bush and Defense Secretary Donald Rumsfeld stood by as a giant U.S. flag was unfurled atop the section of the building that had been destroyed and rebuilt. Bush laid a wreath at the Shanksville-area crash site and mingled with victims' family members, many of whom — like Bush — made the pilgrimage for the first time.

Later, Bush lingered nearly two hours at Ground Zero. His eyes brimming with tears, he embraced fathers, sons and husbands, and kissed mothers, daughters and wives of the 2,801 people killed there.

"We have seen the images so many times they are seared on our souls, and remembering the horror, reliving the anguish, re-imagining the terror is hard — and painful," Bush said. "For those who lost loved ones, it has been a year of sorrow, of empty places."

Nathan Wahlstrom, 25, who lost his grandmother, Mary Alice Wahlstrom, said Bush told him: " 'I'm so sorry. I'll never let this happen again.' The way he was looking at us, you could tell he meant it."

Wahlstrom's brother, Norman Wahlstrom, said: "One lady told him, 'You better get them for getting my boy.' He stopped and looked up, and he said, 'We will.' "

Bush's every move yesterday was accompanied by stringent security as the nation remained on high alert for another attack.

Vice President Dick Cheney was at a secret location and planned to stay there at least until tomorrow. Armed anti-aircraft missiles were deployed around the nation's capital, and military aircraft patrolled the skies over a dozen cities.

After the first moment of silence in New York, Gov. George Pataki read Abraham Lincoln's Gettysburg Address, which promised: "We here highly resolve that these dead shall not have died in vain."

At dusk, New York Mayor Michael Bloomberg oversaw the lighting of an eternal flame in nearby Battery Park, with U.N. Secretary-General Kofi Annan and Secretary of State Colin Powell and numerous foreign dignitaries in the city for tomorrow's opening of the United Nations also participating.

New Yorkers gathered nearby, many staring up at where the twin towers once dominated the skyline, perhaps seeing ghosts, perhaps reliving the horror that played out on television screens across the country all day a year ago.

In Washington, Pentagon secretary Dorothy Powell summed up the feelings of many: "I still can't get over that this actually happened in America."

Bush recalled that day, too, and said the U.S. owes the Sept. 11 victims its best.

"Tomorrow is Sept. 12th. A milestone is passed, and a mission goes on. Be confident. Our country is strong. And our cause is even larger than our country," Bush said.

Compiled from Gannett News Service, The Associated Press and The Washington Post.