LOS ALAMOS, N.M.—No one knows for sure what is buried in the Manhattan Project-era dump here. At the very least, there is probably a truck down there that was contaminated in 1945 at the Trinity test site, where the world's first nuclear explosion seared the sky and melted the desert sand 200 miles south of here during World War II.

But now a team of workers is using $212 million in federal stimulus money to clean up the 65-year-old, 6-acre dump, which was used by the scientists who built the world's first atomic bomb. They are approaching the job like an archeological dig—only with even greater care, since some of the things they unearth are likely to be radioactive, while others may be explosive.

The dump has become part of the $6 billion stimulus program to clean up the toxic legacy of the arms race, which is one of the biggest sources of direct federal contracts in the $787 billion stimulus act. More than $1.9 billion is being spent at the Hanford site in Washington, the home of the nuclear reactor that made the plutonium for the atomic bomb that was dropped on Nagasaki. Another $1.6 billion is being spent cleaning up a Savannah River site, in South Carolina.

After the stimulus bill passed, some Republicans questioned the wisdom of devoting so much money to nuclear cleanups, noting that the Department of Energy's environmental management program had been bedeviled by cost overruns in the past. Democrats countered that the labor-intensive projects would create many jobs while advancing the stimulus act's goal of improving the environment.

They also noted that the money was only a down payment on what is still a staggering task: the Department of Energy is responsible for cleaning up 107 sites, with as much acreage as Delaware and Rhode Island combined, in work that could take decades and cost up to $260 billion to complete.

Nearly 73,000 people have applied for stimulus jobs cleaning up nuclear sites since the program was announced, the Department of Energy says, and more than 10,800 positions have been saved or created with the money.

Here at Los Alamos, some of the first work involves tearing down buildings and cleaning up land at what is called Technical Area 21. It was an isolated mesa in 1945 when the laboratory moved its plutonium processing operations there after a fire broke out uncomfortably close to its original plant near the center of town. But the town has grown since then, and now several businesses—including a hardware store, an auto repair shop and the local newspaper—are right across the street from the old dump.

Since the dump, the laboratory's first, was used only from 1944 through 1948, the cleanup team had to do a great deal of detective work to figure out what might be in it.

“;You look for every possible shred of evidence that you can to give you an idea of what kind of surprises you might encounter,”; said Allan B. Chaloupka, who directs the decontamination and decommissioning program.

The team members pored over wartime classified documents and interviewed old-timers to learn what materials might have found their way into the dump, and took soil samples to test their estimates of how much plutonium might be buried there. They questioned a laboratory worker who, as a young man, once fell into it.

They asked scientists at Los Alamos National Laboratory to come up with worst-case scenarios of how explosive the chemicals dumped there might have grown over the years—and then they blew up the equivalent amounts of dynamite to test all the safety measures that they would be taking. While the laboratory has endeavored to assure the public that the work will be performed safely, some of the site's closest neighbors are eyeing the project warily.

“;You wonder what's going on,”; said Ken Romero, 40, a machinist at the Jona Manufacturing Co., across the street. “;One day we looked across the street and there was a guy in a full-body white suit, and he was just 100 yards away from us.”;

On a recent visit, officials emphasized the extreme care they were taking. When they tore down an air-processing building early one morning, they did not use any explosives, for obvious reasons. Instead, an excavator tore a slice down the center of the building, and then surgically knocked the building's walls inward, so the debris would not hit any of the neighboring buildings.

Some of the workers did wear white body suits, but in this case they were for protection from asbestos, not radiation. The building was not contaminated, though some of its neighbors were.

So far, about 156 people—many from small businesses in the area—have been given jobs on the project, which will ultimately employ roughly 300 people, officials said.

“;Many are basically common laborers that come out of commercial operations,”; Chaloupka said, “;and we're teaching them to do something at a little higher level, and we're creating a cadre of people that can do other jobs later.”;

The government is under a consent order with the State of New Mexico to clean up the area, so there will be more work after the stimulus program ends.

George Rael, an assistant manager for environmental operations at the Department of Energy's site office here, said that by clearing most of the mesa, the stimulus work would send a signal to the public.

“;This is going to be very visible skyline change that people will actually see and recognize,”; Rael said.

Several of the buildings they are tearing down date to the Manhattan Project days, when a secret laboratory hastily thrown up here on the Pajarito Plateau at the site of a ranch school for boys produced the bomb that changed the world.

The complex was top secret: eminent physicists who visited were given pseudonyms, the whole town was behind a fence, and the laboratory's inhabitants all had the same mailing address, “;P.O. Box 1663, Santa Fe,”; which was also used on the birth certificates of babies born there.

When the job here is done, and the waste is dug up and trucked elsewhere, officials said, the mesa will be clean enough for homes to be built on it.