Once again, the city will pause for four moments of silence to mark the attacks that killed thousands. Family members will lay flowers by the fallen twin towers, and the names of more than 2,700 victims will be read.

But much will be different on the sixth anniversary of September 11, 2001, after tense arguments about where to hold the ceremony, if a presidential candidate should be allowed to speak, and whether focus on the commemoration has become excessive.

Firefighters, first responders, and construction workers who helped rescue New Yorkers — and many who later recovered victims’ bodies — were chosen this year to read the names of the dead in a small public park instead of the World Trade Center site.

After bitterly objecting that they wanted to pay their respects closest to where their loved ones died, family members will be allowed to descend to the site below street level and lay flowers near where the towers stood.

“It’s still like visiting a grave on the person’s anniversary of their death,” a woman whose firefighter brother died that day, Rosaleen Tallon, said.

While the list of 2,750 victims killed in New York is read, Osama bin Laden planned to appear in a new video and read the will of one of the hijackers whose plane flew into the north tower.

Politics has played little role in past ceremonies, when siblings, spouses, and children offered heartfelt messages to their lost loved ones. The city’s firefighters, however, could raise several issues — they are among thousands who say they suffer persistent respiratory problems after inhaling dust from the trade center’s collapse. Two firefighters died just last month in a blaze at a skyscraper that had not been torn down since it was damaged on September 11.

And firefighters and several victims’ family members are furious that Mayor Giuliani, who has spoken every year at the ceremony, is doing so tomorrow as a Republican presidential candidate.

“He’s really kind of raining on their coattails a little bit,” Ms. Tallon said.

Mr. Giuliani, who has made his performance in the months after the 2001 terrorist attacks the cornerstone of his campaign, said last week that his appearance wasn’t intended to be political.

“I was there when it happened and I’ve been there every year since then. If I didn’t, it would be extremely unusual. As a personal matter, I wouldn’t be able to live with myself,” Mr. Giuliani said Friday at a campaign stop in Florida. “I will do that for as long as they have a ceremony out there.”

A fire union spokesman said no organized demonstration by firefighters was planned.

Another change in this year’s ceremony will be the list of victims. That is because the official death toll was increased by one this year after the city ruled a woman’s death of lung disease was caused by exposure to toxic trade center dust. The name of that woman, Felicia Dunn-Jones, will be read at the ceremony for the first time.

The anniversary was moved this year because of more intensive construction under way at ground zero, where several cranes overlook a partially built September 11 memorial, transit hub and skyscraper.

Several family members worried that Zuccotti Park, just southeast of ground zero, would be too small to accommodate the thousands of people. City officials said there was actually more space available than at the previous location.

But others have questioned whether the commemoration had become excessive; some New Jersey communities that lost many people in the attacks said their ceremonies were being scaled back.

The city has estimated that fewer people have come to the ceremony each year. One local television station, WABC-TV, initially decided not to air the four-hour-plus ceremony live, although it changed its mind once the public complained.

Mayor Bloomberg said today that the ceremony may continue to change over time.

“I think one of the challenges that we as a society have is how do you keep the memory alive and the lesson of something like 9/11 alive going forward for decades,” he said. “I’ve always thought we should try to change the ceremony each year… you’re going to have to change to keep it relevant.”