The country honored the nearly 3,000 victims of the worst terrorist attack on American soil Thursday with ceremonies in New York, Washington and Pennsylvania to mark seven years since Sept. 11, 2001.

At the White House, President Bush led a moment of silence on the South Lawn at 8:46 a.m., the time that terrorists flew the first commercial jetliner into one of the Twin Towers at the World Trade Center. The second plane crashed into the other tower at 9:03 a.m.

In New York, victims' families and dignitaries paused for four moments of silence Thursday morning to commemorate the precise times that two hijacked jetliners crashed into the World Trade Center, along with the times that each tower collapsed at 9:59 a.m. and 10:29 a.m.

"Today marks the seventh anniversary of the day our world was broken," Mayor Michael Bloomberg said. "It lives forever in our hearts and our history, a tragedy that unites us in a common memory and a common story ... the day that began like any other and ended as none ever has."

Family members and students representing more than 90 countries that lost citizens on Sept. 11, 2001, gathered in Lower Manhattan for remarks and a recitation of the names of the more than 2,700 people killed in New York.

Among the readers was Laraine Angeline, who lost brother-in-law, Steve Pollicino. "Steve, your smiles live on with us," she said. "Our separation is temporary. Our love for you is forever."

Shortly before 9 a.m., families of Sept. 11 victims went down seven stories into the cavern where the towers stood — called Ground Zero ever since this day in 2001 — using the construction ramp on the south side of the 16-acre site to touch the place where their loved ones died before returning to street level.

Relatives of victims began arriving at dawn at Ground Zero, now a huge construction site. American flags were draped over silent cranes and some families held signs saying "We miss you," "We love you" or "You will never be forgotten."

Maureen Hunt, wearing a T-shirt with a picture of her sister, Kathleen, a 9/11 victim, said that it was comforting to be at the ceremony with so many who have lost loved ones.

"This is a place for us to meet," said Hunt, who has come each year to pay her respects. "It is not getting easier to attend these ceremonies."

The family of Sept. 11 victim Michael Diehl went to Ground Zero wearing white T-shirts bearing his photo and 9/11/01.

"It's still very hard for us to come here. It doesn't get any easier," said Diehl's sister-in-law, Norma Linguito. "I just wish they'd get the memorial up so we can have something, a marker, to remember everyone."

Bush said Thursday that history will look back at America's response to the Sept. 11 terror attacks and conclude that "we did not tire, we did not falter and we did not fail."

After the White House remembrance, Bush headed to the Pentagon in Washington to dedicate a memorial to each life lost when American Airlines Flight 77 hit that building — a symbol of American military prowess — in the third strike that morning.

The Pentagon monument consists of 184 benches, one for each victim, that overlook small reflecting pools. The Defense Department's headquarters were struck about an hour after the attacks in New York.

A fourth plane that was apparently headed for the White House or the Capitol building in Washington crashed prematurely in a field in Shanksville, Pa. A ceremony was also held there.

Barack Obama and John McCain, the Democratic and Republican presidential nominees, appeared together at Ground Zero in New York on Thursday afternoon after the ceremony ended to honor those who died. They were escorted by Bloomberg, and threw roses on a memorial.

The campaigns agreed to halt television advertising critical of each other for the day.

McCain also attended the service in Shanksville for the 40 people killed there aboard United Airlines Flight 93.

Obama called on Americans Thursday to renew "that spirit of service and that sense of common purpose" that followed the attacks. McCain asked every person "to be as good an American" as the passengers and crew of United Airlines Flight 93 after they rose up against the hijackers.

In Pennsylvania, at least 200 people gathered Thursday morning at an observance in a reclaimed minefield in Shanksville where Flight 93 came down after passengers reportedly stormed the cockpit to thwart terrorists' plans to use that plane as a weapon like the others. Bells tolled and victims' names were read as part of the service.

Some mourners in New York wondered if the remembrance would, or should, continue as it has indefinitely. About 3,500 people attended last year's ceremony, a roughly 25 percent decrease from 2006.

"We've kept it alive, and perhaps kept it alive too long," said Charles Wolf, whose wife, Katherine, was killed at the World Trade Center. "How many times do you reopen the wounds?"

Other victims' relatives worry that Sept. 11 will revert to being just another date on the calendar.

"The remembrances have to continue; for how long, I can't say," said Barbara Minervino of Middletown, N.J., whose husband, Louis, died in the towers.

The New York ceremony included the reading of 2,751 victims' names, one more than last year. The city restored Sneha Philip, a woman who vanished on Sept. 10, to its official death toll this year after a court ruled that she was likely killed at the trade center.

Former Mayor Rudy Giuliani spoke at the commemoration, as he has every year, along with officials including Bloomberg and Homeland Security Secretary Michael Chertoff.

Last year's reading by Giuliani, then a Republican presidential candidate, drew protests from family members who said the city was ill-prepared for the terrorist attacks under his leadership and questioned whether he should be there while running for the White House. They had no opposition to McCain and Obama' visit this year.

Joining the president at the White House and the Pentagon were first lady Laura Bush, Vice President Dick Cheney and his wife Lynne, members of Congress, Cabinet members, military officials and about 3,000 White House employees and guests.

The Pentagon ceremony included a wreath laying, music and a reading of the names of those who died on the plane and inside the building. Defense Secretary Robert Gates spoke.

"This memorial tells the story to future generations," Gates said. "They won't directly feel the heat, smell the smoke or know the horror of that day, but they will know, as the inscription says, that we claim this ground."

Former Defense Secretary Donald Rumsfeld mourned those who "one morning kissed their loved ones goodbye, went off to work and never came home" and the airline passengers "who in the last moments made phone calls to loved ones and prayed to the Almighty before their journey ended not far from where it began."

The Pentagon Memorial was built at a cost of $22 million on a 1.9-acre parcel of land adjacent to the Defense Department building and within view of the crash site.

Memorials are years away from being built in Pennsylvania and New York. As in past years, two bright blue beams of light will shine at night on the New York City skyline, in memory of the fallen towers.

The Associated Press contributed to this report.