NEW YORK — Relatives of victims killed at the World Trade Center arrived at dawn Thursday for ceremonies that will commemorate the seventh anniversary of the Sept. 11 attacks and bring both presidential candidates to ground zero later in the day.

Moments of silence were planned to mark the times that two hijacked jetliners crashed into the twin towers, along with the moments that the buildings collapsed. Services were also to be held in Pennsylvania and at the Pentagon, where a new memorial will be dedicated.

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.’’

She said she won’t go down into the pit where the towers once stood, and which some survivors consider sacred ground. It is now a huge construction site. On Thursday, American flags were draped over silent cranes.

‘‘Eventually, I hope that something gets built,’’ Hunt said, referring to the long-stalled rebuilding of the site.

This year the solemn events unfold amid a presidential campaign, with John McCain and Barack Obama scheduled to pay silent respects at ground zero Thursday afternoon and later attend a New York City forum on public service. McCain was also attending Thursday’s memorial service in Shanksville, Pa., for the 40 people killed aboard the hijacked flight United 93.

Family members and students representing more than 90 countries that lost victims on Sept. 11 were to read names of more than 2,700 people killed in New York. Some mourners wondered if the remembrance would, or should, continue as it has indefinitely.

About 3,500 people attended last year’s ceremony, down about 25 percent 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?’’

Wolf, who lives in downtown Manhattan, attends the ceremony every year but said it has become more painful, especially to stand in silence for the moment that a plane crashed into the tower where his wife worked. ‘‘It’s one thing to remember,’’ he said, ‘‘but it’s another to relive it.’’

The ceremony moved to a park just east of ground zero last year because of construction at the trade center site. But family members are allowed to descend seven stories below ground to the site and touch the spot where their loved ones died.

The ceremony will include the reading of 2,751 victims’ names, one more than last year. The city restored Sneha Philip, a woman who mysteriously vanished on Sept. 10, 2001, to its official death toll this year after a court ruled that she was likely killed at the trade center.

McCain and Obama planned to visit the site after the ceremony concluded Thursday afternoon. The candidates agreed weeks ago to pull their campaign ads for the day and were appearing together Thursday night at a forum on volunteerism and service.

Former Mayor Rudy Giuliani was to speak at the ceremony, as he has every year in New York, along with officials including Mayor Michael Bloomberg and Homeland Security Secretary Michael Chertoff.