A bell tolled 40 times Wednesday, once for each victim of United Flight 93, as thousands of people gathered in a grassy field remembered the passengers and crew hailed as heroes for struggling to take back their hijacked plane.

"These 40 amazing, extraordinary people had character in abundance," said Homeland Security Director Tom Ridge, who was governor of Pennsylvania at the time of the terrorist attacks. "They were heroes every single day."

One crew member used to save airline meals to feed the needy, he said. Another victim helped restore a shelter for battered women, and yet another volunteered at a crisis pregnancy center.

"Today is not just to mark their tragic and honorable deaths, but to celebrate their lives and mark a nation's gratitude for their actions," Ridge said. He hailed them as "citizen-soldiers" and "America's 21st century patriots."

Ridge's remarks were followed by a rifle salute and the release of 40 doves.

President Bush, who attended a morning ceremony at the Pentagon, arrived at the field around noon and strode through knee-high grass with first lady Laura Bush to the spot where the airplane crashed.

Bush bowed his head with the families gathered there while a Marine laid a wreath as trumpeters played taps. Afterward, he shook hands and spoke privately with the relatives.

During the ceremony, 11-year-old Murial Borza, who lost her half-sister, Deora Bodley, asked the audience of more than 5,000 for a minute of silence for world peace.

Sandy Dahl, the wife of Flight 93 pilot Jason Dahl, said, "If we learn nothing else from this tragedy, we learn that life is short and there is no time for hate."

The tolling, accompanied by the reading of each victim's name, led up to the moment that the plane crashed at 10:06 a.m. last Sept. 11 in a field about 70 miles southeast of Pittsburgh. Investigators say people on board confronted the four hijackers and brought down the plane far from an intended target in Washington, possibly the White House or Capitol.

The crater that had been left by the plane was filled months ago and replanted. The only evidence of the crash is a metal fence to keep people from digging at the site, considered both a cemetery and a crime scene, and the flags, photographs and flowers left as a memorial to the victims.

"It helps me a lot to know it's such a beautiful place," said Alice Hoglan, 52, of Los Gatos, Calif., whose son Mark Bingham died in the crash. She joined more than 500 relatives and friends of the victims who toured the crash site privately Tuesday.

"The most important thing to me is that we do not forget," said Hamilton Peterson of Bethesda, Md., whose father and stepmother were killed.