Presidential candidates Senator McCain and Senator Obama made ground zero their common ground for one rare day, free of politics and infused with memory.

Putting their partisan contest on a respectful hold, they walked together today into the great pit where the World Trade Center once stood and, as one, honored the dead from the terrorist attacks of Sept. 11, 2001.

They walked down a long ramp flanked with the flags of countries, chatting at times, silent other times, and sharing a quick laugh at one point. Right behind them, Cindy McCain clutched Mayor Bloomberg’s arm — Michelle Obama was with her daughters in Chicago.

At the bottom of the ramp, the two rivals stopped to talk with a small group of family members of the attacks’ victims of seven years ago. They laid flowers at the pit’s commemorative reflecting pool — a pink rose from Mr. Obama, a yellow rose from Mr. McCain — bowed their heads and walked off to speak with fire and police personnel. There were no speeches.

“Thanks, we’ll see ya,” Mr. McCain told Obama as the Democrat patted the Republican’s back and they shook hands and parted.

Earlier, Mr. McCain spoke briefly at a simple ceremony in remote, rural western Pennsylvania, held on a large hilly field close to where United Airlines Flight 93, the third of four airliners commandeered by terrorists, crashed. Investigators believe some of the 40 passengers and crew rushed the cockpit and thwarted terrorists’ plans to use that plane as a weapon like the ones that hit the World Trade Center and Pentagon. All aboard all planes died.

The Arizona senator said those on the flight might have saved his own life, as some believe the terrorists wanted to slam that plane into the U.S. Capitol. He said the only way to thank those who died on the flight is to “be as good an American as they were.”

“We might fall well short of their standard, but there’s honor in the effort,” Mr. McCain said.

Mr. Obama, in a statement, said that on Sept. 11, 2001, “Americans across our great country came together to stand with the families of the victims, to donate blood, to give to charity, and to say a prayer for our country. Let us renew that.”

The Illinois senator added: “Let us remember that the terrorists responsible for 9/11 are still at large, and must be brought to justice.”

Left unstated by both was their sharp disagreement over the Iraq war, which Mr. McCain supported and Mr. Obama opposed as a distraction from the Afghanistan war and broader fight against terrorism.

It was not a day for spelling out differences but rather a respectful time out in a campaign with 54 days to go. Both agreed to suspend TV ads critical of each other.

In Pennsylvania, grieving family members and a few dignitaries sat in front of a chain-link fence adorned with flags and mementos that serves as a temporary memorial while a permanent one is built. Bells were rung as the name of each victim was read. Mr. McCain and others laid wreaths at the foot of two flagpoles and a large wooden cross.

The political truce was evident in remarks thanking Mr. McCain for traveling to Shanksville by Pennsylvania Gov. Ed Rendell, a Democrat who occasionally speaks against the Republican nominee as an Obama campaign surrogate. “It’s an honor to have him here, not just as a presidential candidate but as a great American patriot,” Mr. Rendell said.

Mr. Obama and Mr. McCain were intersecting again later, at a Columbia University forum on public service in the evening. Their sessions at the forum were separate.

Mr. Obama’s only other planned outing Thursday was lunch in New York with former President Clinton.

Mr. Obama’s running mate, Joe Biden, was going to an American Legion post in suburban Cleveland with an invitation-only gathering of area police, firefighters and other first responders. The Republican vice presidential candidate, Sarah Palin, was in her home state of Alaska, attending an Army ceremony to send her eldest son, Track, off to duty in Iraq and doing interviews with ABC News.

Mr. Obama and Mr. McCain last appeared together in August when they shook hands at minister Rick Warren’s megachurch in Orange County, Calif., where they spoke separately about faith and values. In June they attended the funeral of NBC newsman Tim Russert, sitting next to each other at the family’s request.