Grieving relatives of World Trade Center victims assembled at a lower Manhattan park today to mark the sixth anniversary of the September 11, 2001, attacks, with gray skies and rain providing a grim backdrop to the first ceremony not held at ground zero.

The move prompted some families to skip this year’s memorial, which was also the first time the commemoration has been held on a Tuesday — the day the attacks occurred in 2001 — and the first time it has rained.

Once again, the city paused to listen as the names of the 2,750 victims were read in a familiar but still-moving litany. And once again, after winning a dispute with city officials, family members marched into the pit at ground zero to remember their relatives whose lives ended in the fiery rubble of the collapsed 110-story towers.

Among the first family members down the ramp was a woman whose late husband Joel worked at Marsh & McLennan, Marjorie Miller. She said the rain was almost welcome after five consecutive years of September 11 sunshine.

“A lot of tears coming down from up there,” she said, gesturing toward the sky, “and a lot of tears down here.”

Nearly 2,000 mourners descended into the pit by 11 a.m., with some wondering if it was the last time they would gain access to what many consider hallowed ground — although it now more resembles a huge construction site. A rainbow of multi-colored umbrellas marked the slow procession down to the site.

Presidential politics and the health of ground zero workers loomed over this September 11 perhaps more than at any other anniversary. Firefighters shared the stage with Mayor Giuliani, whose presidential campaign led many victims’ families and firefighters to oppose his role in the event.

But Mr. Giuliani was greeted with a smattering of applause after his brief remarks, which followed the third of the traditional four moments of silence: one each for to mark the times when the two planes hit the buildings, and two more for when each tower fell.

“It was a day with no answers, but with an unending line of people who came forward to help one another,” Mr. Giuliani, who was in the final weeks of his eight-year run at City Hall, said

At the pit, a short distance from where Mr. Giuliani spoke at Zuccotti Park, families plucked roses from three buckets at the top of the ramp and marched slowly down to a circular pool of water, which rippled from the raindrops and reflected the dark skies above.

Inside the pool, two smaller 6-foot square pools represented the trade center as family members tossed flowers into the water or wrote messages to lost souls on its wooden perimeter. The family members threatened to boycott the ceremony and hold their own shadow remembrance if they were not granted access.

Even after six years, the pain of that morning lingered for many.

“We’re still very much affected by it on a daily basis,” a woman whose sister Marlyn was killed, Tania Garcia, said. “It’s something we will never get over. It’s an open wound, and every year that passes by just get worse and worse and worse.”

The ceremony began at 8:40 a.m. with the sounds of drums and bagpipes, as an American flag saved from the site was carried onstage. “The Star-Spangled Banner” was performed by the Brooklyn Youth Chorus before the first moment of silence was observed at 8:46 a.m. — the minute the first plane struck the north tower.

Mayor Bloomberg, who has presided over each of the anniversary events, described September 11, 2001, as “the day that tore across our history and our hearts. We come together again as New Yorkers and as Americans to share a loss that can’t be measured.”

As in years past, people clutched framed photos of their lost loved ones, raising them toward the sky, or held bunches of flowers against their chests.

The recitation of the victims’ names began shortly after the moment of silence, with firefighters and first responders who helped rescue New Yorkers handling much of the duties. The group included a former EMS worker who lost two friends after they responded on 9/11 and developed fatal illnesses, Bonnie Giebfried.

An emergency medical technician, Timothy Keller, 41, died in June 2005 after becoming so sick that he coughed up bits of gravel. And Deborah Reeve, who worked for months around ground zero and the city morgue, died in March 2006 of an asbestos-related cancer.

A woman whose niece, Kathleen Casey, was killed in the attacks, Bonnie Giebfried, said she didn’t care about small changes that were made to the ceremony this year. The commemoration had to be moved off ground zero because of all the construction at the site.

“Just so long as we continue to do something special every year, so you don’t wake up and say, ‘Oh, it’s 9/11,” the 54-year-old woman said.

Other September 11 commemorations were held around the country, including a moment of silence by President Bush at the White House. Mr. Bush was joined by his wife, the vice president, Cabinet members, and White House workers as they somberly marked the anniversary.

A memorial honoring the 40 passengers and crew who died when United Airlines Flight 93 crashed in a Pennsylvania field was also held.

“As American citizens we’re all looking at our heroes,” a woman whose sister Colleen Fraser died in the crash over Pennsylvania, Kay Roy, said. “These are our heroes and I’m glad that one of my family members happens to be one of these heroes.”

The homeland security secretary, Michael Chertoff, made an unannounced visit to the 30-minute ceremony honoring the victims of Flight 93.

Mr. Chertoff echoed Governor Rendell’s comments that the passengers and crew were “citizen soldiers” in the war on terror.

For the first time this year, a victim who did not die at the trade center was recognized — the city added the name of an attorney who died of lung disease five months later to its official victims’ list this year. Many of the first responders have become sick, or died themselves, of respiratory problems and cancers they blame on exposure to World Trade Center dust.

Along with Mr. Giuliani, Senator Clinton — seeking her own party’s presidential nomination — attended the ceremonies.

There was no demonstration by the fire union during Mr. Giuliani’s appearance, or to address last month’s blaze that killed two firefighters at a nearby skyscraper that was never torn down despite suffering heavy damaged on September 11.

The toxic tower was in view of people attending the ceremony, providing another grim reminder of the September 11 legacy six years later.