When a World War II weapons plant in Middlesex, N.J., was being rebuilt in the late 1940s, a dump truck driver dropped off a couple of loads of its rubble at his local Catholic church.

Everything from the plant site was supposed to go to a government landfill, but Our Lady of Mount Virgin parish needed some fill for the yard of its new rectory, and no one missed the dirt.

Until last summer.

Suddenly the Department of Energy threw up an eight-foot fence around the rectory and sent men in protective suits and respirators to dig up the entire yard, haul it back to the plant site and seal it in plastic.

Our Lady's lawn was radioactive.

The Middlesex plant had been used to process uranium ore for the Manhattan Engineering Project that created the first atomic bomb.

Now, 35 years after the bomb was dropped on Hiroshima and Nagasaki, the government finally is going to clean up the bomb's birthplaces. Millions of tons of slightly radioactive material still are scattered around 30 World War II-era atomic research sites in 13 states.

Finding and disposing of Manhattan Project leftovers alone will cost an estimated $360 million and take 10 years. By the time some other atomic research sites are cleansed of radioactivity, the nuclear housecleaning could cost close to $2 billion. The job probably will take 20 years, estimates Robert Ramsey, the engineer at the Energy Department in charge of the work.

The Energy Department in the past has had trouble getting funds to pay for the cleanup but now apparently had found a way to get support for it. On Christmas Eve, the agency decided to offer the assignment to a private contractor with close ties to President-elect Ronald Reagan, Bechtel Corp. of California.

The department is negotiating a $140 million five-year contract with Bechtel, whose chairman is S. D. Bechtel Jr., a friend and confidant of Reagan's. Bechtel's president is George P. Shultz, Treasury secretary in the last Republican administration, and its vice president is Caspar W. Weinberger, Reagan's choice for secretary of Defense.

Bechtel will supervise the cleanup of radioactive material that's been lurking for years in housing projects, shopping centers, factories, airports and college campuses.

As Energy Department officials discovered when they started cleaning the Jersey plant last summer, not all of the nuclear debris is where it's supposed to be.

Most of the material that has to be cleaned up is contaminated with what Ramsey calls "super-low levels of radiation."

A person walking across any of the sites would be exposed to less radiation than on a clear day high in the Rocky Mountains, where cosmic rays and natural radiation from rocks are enough to set a Geiger counter clicking.

Someone working 40 hours a week on the sites would get radiation exposure equivalent to "several chest X-rays a year," said Lee Keller, an engineer at the Energy Department's Oak Ridge Laboratory who is assigned to the cleanup.

Keller said there is "no assessment of any change in mortality associated with any of these sites. They pose minimal, if any, hazard to the public at the present time."

The Energy Department's dilemma is how to convince people that the radiation hazards aren't serious enough to cause panic but are serious enough to spend $2 billion to eliminate, Ramsey said.

"We're dealing with a highly sensitive area for the public," he added. "We're trying to do this with a minimum of alarm."

Describing the Energy Department's approach as "very conservative," Ramsey said the agency decided to go over every Manhattan Project site with Geiger counters. "Our philosophy is, if it clicks a counter, move it," he said.

The sites "aren't dangerous," he stressed, "but under certain circumstances you could exceed the radiation exposure levels allowed by the Environmental Protection Agency."

Based on growing concern about the effects of small doses of radiation, the EPA soon will release new federal standards for the amount to which people should and should not be exposed.

The radiation at the contaminated sites is measured in microcuries and picocuries -- meaning that millionths and trillionths of the material is radioactive.

Even at these minuscule levels, however, the radioactivity can build up to unacceptable levels. In the basement of a building erected atop the Manhattan Project sites, radioactive radon gas can accumulate to produce higher radiation levels than in a uranium mine, Ramsey said.

That's what happened in Grand Junction, Colo., where a housing development was built on fill from an abandoned uranium-processing plant. Fear of cancer caused the government to launch a massive project to dig up thousands of tons of spent uranium ore that was used to fill in around the basements of 750 homes and a school. That work started four years ago and is about half complete.

There are an estimated 20 million tons of uranium mill tailings, as the spent ore is called, at two dozen abandoned sites, mostly in western states where it was mined. As much as half that radioactive rock will have to be moved to new locations, where it will be covered with a thick layer of earth to shield it.

Bechtel's assignment will be to get rid of the less-radioactive material from World War II Manhattan Project sites and early Atomic Energy Commission research centers. Ramsey said most of the sites are [TEXT OMMITTED]

The Manhattan cleanup is code-named FUSRAP -- Formerly Utilized Sites Remedial Action Rpogram.

No other industry has ever attempted such a massive cleanup program to dispose of its wastes, Ramsey noted. Abandoned steel mills are allowed to rust into oblivion and so are oil refineries contaminated with cancer-causing hydrocarbons that are perhaps more dangerous than low-level radiation, he said.

The Energy Department, which inherited the job when it took over the Atomic Energy Commission, is running FUSRAP from its Oak Ridge operations center.

After soliciting proposals from more than 100 contractors, Oak Ridge last fall narrowed the choice of a project manager to three firms -- Bechtel, Ford Davis & Bacon and Rockwell International.

Although the other contractors had the impression in October that Bechtel was out of the running, the politically-well-connected contractor was chosen for the job last month.

Keller, the Oak Ridge project engineer, said Bechtel was chosen after a competitive selection process but not on the basis of bids. "We were impressed with the cohesiveness and competence of their proposal," he said.

Congress hasn't appropriated money for the contract, which provides for a possible five-year extension that would raise the total to $350 million.

Bechtel will study 31 Manhattan Project sites, to determine how the radioactivity should be handled and hire subcontractors to do the work.

"We know that at each of the sites some form of remedial action is necessary, but we don't know what," Keller said. The work likely will involve tearing down some buildings, moving an estimated 600,000 cubic yards of contaminated soil and covering some of the sites with a 10-foot layer of clay and dirt to contain the radiation.

The Energy Department prepared for the work by starting last summer with the Middlesex, N.J, plant where uranium ore was sorted and processed after being imported from the Belgian Congo in the early '40s.

It was while flying over the site with sensitive aerial radiation gear that the DOE discovered the old plant was not the only place in Middlesex that was radioactive. Some soil from the site apparently had washed onto adjacent land, and two isolated "hot spots" showed up.

One turned out to be the home of a workman on the 1940s construction project; DOE officials assume he asked a friend for some fill dirt from the job. The other was Our Lady of Mount Virgin's rectory.

Fill from the uranium warehouse site had been dumped around the rectory's foundation, then covered with top soil. "The whole yard was laced with uranium ore," said DOE engineer Ramsey.

The contractor hired by the Energy Department dug up the yard, excavated down to the foot of the foundation and scrubbed down the outside of the basement walls to remove any traces of contamination.

Although government officials told the Rev. Joseph Fibner's parishioners and neighbors there was no danger from the work, the precautions they took were not reassuring.

Workmen on the job wore protective clothing and breathed through respirators to keep the radioactive dust out of their lungs. They put a plywood fence around the project to keep the material from straying onto neighboring lawns. And, in the midst of a severe drought when lawn-watering was banned, DOE soaked the diggings constantly to eliminate dust.

DOE officials won't say what it cost to repossess their uranium waste and rebuild Our Lady's lawn; the four jobs in Middlesex cost $3 million.

Using what was learned in the New Jersey cleanup, the FUSRAP project in the next five years is supposed to follow the path of the Manhattan project, sweeping up the droppings. The radioactive trail starts at the Bayonne, N.J., docks where uranium ore was unloaded and leads to a Staten Island, N.Y., warehouse where ore was stored.

It touches uranium-processing plants in St. Louis; Niagara Falls, N.Y.; and Deepwater, N.J. At Curtiss Bay, near Baltimore, a W.R. Grace uranium ore facility has to be decontaminated. On the campus of Iowa State University in Ames, a historical marker shows where pioneer research on making pure uranium metal was done and where the cleanup will be needed.

DOE researchers combed the once-secret files of the Manhattan Engineering Project, identifying every contractor involved and more than 100 different sites where radioactive material was handled. Several of the companies went out of business long ago, so the DOE used old Yellow Pages to locate where they had been.

"We should have gotten started on this by 1960 at least," Ramsey acknowledges. "If we go any longer it's going to take so many resources to catch up."