Atop the tallest man-made hill on the eastern seaboard, hundreds of FBI agents, experts and volunteers sift through the World Trade Center debris, looking for any piece of evidence. 

For six days, a round-the-clock parade of heavy-duty dump trucks loaded with wreckage and flatbed trailers carrying twisted steel beams has crossed the Verrazano Bridge, turned off Route 440 and chugged up the incline to the Fresh Kills landfill on Staten Island.

``It's the ideal site to sift through the material,'' Kevin Farrell, the city's sanitation commissioner, said Tuesday.

His agency used the 3,000-acre dump for 53 years until it was officially closed last March — much to the relief of nearby residents.

Fresh Kills, its name taken from the Dutch word for water, opened in 1948 as a ``temporary'' site. The inaptly named dump took in 2 billion tons of refuse over its lifetime, growing to three times the size of Central Park. A 200-foot-high ridge runs down the middle of the dump.

Months after closing, Fresh Kills is back in business. Behind tight security, 800 workers from city police and fire departments, the FBI, Secret Service, Bureau of Alcohol, Tobacco and Firearms, National Guard and outside volunteers work 12-hour shifts. Seagulls wheel over a newly erected tent city.

As of Tuesday, 45,000 tons of debris sorted at Fresh Kills had yielded 256 body parts, many personal belongings and ``several'' knives and box cutters, officials said. It was not known whether these were the weapons used by the hijackers to take over the two aircraft that hit the twin towers.

Still unaccounted for were the FBI's top priorities: four orange-painted flight data and cockpit voice recorders from the Boeing 767s that caused both 110-story skyscrapers to collapse.

Body parts are photographed, tagged and stored in refrigerated trucks. Airplane parts are set aside, as are personal items police hope to return to their owners or their families.

``It's gruesome work, it's depressing,'' said police Lt. Ray Sheehan, a crime scene expert.

Police Commissioner Bernard Kerik said many ex-cops volunteered to help sift the wreckage, among them a retired detective seeking something belonging to his son-in-law, missing in the disaster.

``It's a very emotional process,'' Kerik said.

No part has been more painful than the retrieval of 10 ladder trucks, five fire engines and several support vehicles, battered reminders of the nearly 300 firefighters who perished, most of them buried when the first tower collapsed.

Firefighters' jackets, helmets and other effects were stored in one tent, which was being treated as a shrine, said fire Lt. Peter Cassidy of Linden, N.J.

Scores of other vehicles caught under the falling debris formed a bizarre junkyard — utility trucks, private cars and some with ``official'' license plates, possibly the remains of the Secret Service fleet housed in a basement garage.

A 10-foot by 15-foot American flag with the notation ``130 Liberty Plaza,'' a building across the street from the Trade Center, flew overhead as a tribute.

``We are all united to achieve a common goal. The entire thing is humbling,'' said Deputy Police Inspector James Luongo, the officer in charge.

Outside the gate, three red-beret members of the Guardian Angels, the private safety patrol, waved American flags and cheered as each truck, car, National Guard Humvee or Red Cross van arrived and departed.

``We want to help any way we can. We had Guardian Angels at the scene since the first plane hit. We helped there, and now we're here to encourage these workers coming back and forth,'' said Jose Gonzalez, 25, of New York.

The drivers clearly appreciated the gesture, sounding diesel horns and flashing thumbs-up salutes. One grinned as he held up a newspaper with a photo of suspected terrorist mastermind Osama bin Laden and the headline, ``Wanted, Dead or Alive.''

Tania Falcone, 21, a waitress from New York, said her decision to join the support effort ``got me fired from my job.''

``But hey, I'm not worried about it,'' she shrugged. ``I had to be at my job but I wanted to be with the Angels.''