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, six-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.