NEW YORK -- Sens. John McCain and Barack Obama have been sharing some common ground -- at New York's ground zero. As the country marks the seventh anniversary of 9/11, the two presidential candidates put aside politics to honor the victims and express appreciation for those who responded to the attacks.

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The two walked side-by-side down a long walkway into the pit where the World Trade Center once stood. They were accompanied by New York Mayor Michael Bloomberg and McCain's wife, Cindy. Michelle Obama was in Chicago where the couple's daughters recently began a new school year.

The Republican and Democratic nominees could be seen chatting as they walked and even shared a quick laugh at one point. At the bottom of the ramp, they talked with a small group of family members of the victims. They also laid flowers at a commemorative reflecting pool before walking off to speak with firefighters and police.

Beforehand, McCain spoke briefly at a ceremony in rural western Pennsylvania. The event was held on a large hilly field close to where United Airlines Flight 93, the third of four airliners commandeered by terrorists, crashed.

McCain spoke of the passengers and crew who investigators believe rushed the cockpit to thwart the hijackers' plans to use the plane as a weapon, possibly to hit the U.S. Capitol.

McCain said his own life may have been saved that day. He said the only way to thank the heroes of that flight is to "be as good an American as they were."

In a statement Thursday morning, Obama called on Americans to "renew that spirit of service and that sense of common purpose" that followed Sept. 11, encouraging people to donate blood, give to charity and "say a prayer for our country."

Obama and McCain set aside presidential politics Thursday to remember the Sept. 11 attacks. The candidates had agreed weeks ago to pull their campaign ads for the day.

Relatives of people killed at the World Trade Center on Sept. 11, 2001, said the decision by Obama and McCain to appear together at ground zero on the seventh anniversary of the attacks is a welcome gesture of respect.

"I think it's a wonderful thing," Sally Regenhard, whose son, Christian, was killed at the trade center, said Monday. "I assume that they're coming down here to pay respects to the people who lost their lives and to really affirm the fact that this is sacred ground for America."

Others said being there was enough.

Rosaleen Tallon, who lost her brother, Sean, a rookie firefighter, said they should not speak.

"It should just be where they're paying their respects," she said.

Moments Of Silence

From New York's ground zero to the Pentagon and a rural field in Pennsylvania on Thursday, the nation paused to mark the anniversary.

Relatives of victims killed at the World Trade Center gathered for a ceremony that included the reading of victims' names and moments of silence at 8:46 a.m. and 9:03 a.m. Eastern time, when two hijacked jets slammed into the twin towers seven years ago.

Two more moments of silence were scheduled to be held at the times the towers fell.

New York Mayor Michael Bloomberg opened the ceremony by telling the tearful audience: "Today marks the seventh anniversary of the day our world was broken. It lives forever in our hearts and our history, a tragedy that unites us in a common memory and a common story."

Former New York Mayor Rudy Giuliani also spoke, saying, "The entire world is linked in our circle of sorrow."

In Arlington, Va., a ceremony was held to dedicate the Sept. 11 memorial at the Pentagon. The 2-acre park consists primarily of 184 benches, each bearing a victim's name.

At the Pentagon dedication, President George W. Bush said the terrorists could not break the resolve of the U.S. armed forces.

He said that "since 9/11, our troops have taken the fight to the terrorists abroad so we do not have to face them here at home." Bush added: "Thanks to the brave men and women, and all those who work to keep us safe, there has not been another attack on our soil in 2,557 days."

The ceremony included a wreath laying, music and a reading of the names of those who died on Flight 77 and inside the building.

At White House

Bush led a moment of silence at the White House, joining scores of invited guests and staff in observing the seventh anniversary of the terrorist attacks that killed nearly 3,000 people.

Standing next to the president under threatening skies for the brief South Lawn ceremony were his wife, Laura, and Vice President Dick Cheney and his wife, Lynne.

The moment of silence, as church bells peeled, was observed at 8:46 a.m. EDT, the exact moment in 2001 when terrorists crashed a hijacked airplane into the World Trade Center in New York.

Every year since, Bush has stood in silence on the South Lawn to remember the people who died at the World Trade Center in New York, the Pentagon and a field in Shanksville, Pa.

A chorus sang "God Bless America."

The assembled crowd numbered in the hundreds and included leaders of Congress, members of the Cabinet, diplomats, men and women in military uniform and chefs, plumbers, ushers and others who work at the White House.

Turning Point For Bush

The attacks were a turning point for Bush, an inexperienced, little-traveled president who had shown marginal interest in world affairs.

Before Sept. 11, 2001, Bush was best known for winning his office in a controversial Supreme Court decision and then cajoling Congress into passing one of the largest tax cuts in history and enacting a major education bill.

After Sept. 11, 2001, Bush declared himself a wartime president. He denounced "evildoers" and launched a global war on terrorism. He rallied the nation and the world, and his approval ratings soared.