Energy Secretary Bill Richardson ordered a 24-hour "safety stand down" at the agency's Paducah, Ky., uranium plant yesterday after a preliminary probe uncovered lapses in programs designed to protect workers from harmful radiation.

The announcement is expected to idle about 400 workers for a day while officials begin a comprehensive review of training and radiation monitoring at the Paducah Gaseous Diffusion Plant.

The safety order applies to employees of the Department of Energy and its contractors at the site but will not directly affect the plant's uranium operations, which are now managed by a private corporation, U.S. Enrichment Corp., under the Nuclear Regulatory Commission's oversight. USEC employs about 1,400 people and says it is unaware of any significant safety problems.

"This will be an effective way to focus attention," Richardson said in an interview before the announcement, "and also a way to get managers and workers to bring renewed attention to environment, safety and health."

Richardson's action comes exactly a month after he launched a major probe of worker exposures at Paducah, a producer of enriched uranium for nuclear weapons and power plants since 1952. The investigation followed reports in The Washington Post about radioactive contamination at the plant, including revelations that thousands of workers had unwittingly handled materials tainted with plutonium and other highly radioactive metals.

The revelations led to a rash of new discoveries of contamination at Paducah and other DOE facilities, and triggered a $10 billion class action lawsuit against the plant's former operators.

Although DOE investigators have not completed their analysis, agency officials said the team has found no "imminent hazards" to workers or the public. A formal report on current conditions at the plant is due to be released by the end of the month. A second, more ambitious study will delve into workplace hazards, including plutonium, that existed at the plant before 1990.

The Paducah safety order was based on the "preliminary observations" of a team of DOE inspectors who completed an initial sweep of the 740-acre plant last week. Although specific findings were not released, agency officials had expressed concern about a wide range of safety issues at the plant, including whether workers were being adequately monitored and trained for the radiation hazards they face on the job.

In the past two weeks, several clean-up programs at the plant have been disrupted by revelations of improper safeguards for workers. In one incident, DOE investigators discovered that construction workers had been laboring for months in a contaminated area without proper training or radiation-monitoring badges.

Other stories about inadequate safeguards have come from workers themselves.

Agency officials said they intend to use the 24-hour suspension to drill workers on radiation protection measures and to inspect known contaminated areas to make sure warning signs are properly posted.

"We will also remind workers of the presence of plutonium and other transuranics on site," said Jimmie Hodges, the DOE's top manager at the site.

A lawsuit filed in June by three Paducah workers alleges that plant officials failed for years to warn workers about plutonium and other hazards at the plant. Plutonium, a powerful carcinogen, slipped into the plant in shipments of contaminated uranium during the 1950s, '60s and '70s.

The suit also accuses former contractors of dumping contaminated material outside the plant fence -- both in a sanitary landfill and in a wooded area that is now part of a state wildlife park. Small amounts of plutonium have been detected in ditches and streams outside the plant, and radioactive technetium has contaminated drinking water supplies in a nearby residential neighborhood.

Richardson, in announcing the Paducah probe last month, pledged to seek expanded compensation for workers whose health was put at risk. "I will not rest until these issues are fully dealt with and any injured workers are fairly compensated," he said.

In a separate development, Energy officials yesterday also cited the agency's Los Alamos National Laboratory for safety violations stemming from a pair of accidents that spread radiation in a chemistry lab in the New Mexico complex.

One incident involved the radioactive contamination of a lab worker. The worker was exposed both internally and externally after opening an unmarked canister that contained radioactive material.

The same lab was contaminated a second time in June when a piece of equipment ruptured, spattering the room with radioactive material. While DOE labs are exempt from civil penalties, the same safety lapses at another facility would have resulted in fines of more than $200,000, agency officials said.

"We are most concerned that these problems continue to repeat themselves and that laboratory management -- despite commitments made in previous enforcement actions -- has failed to correct identified problems," said David Michaels, the DOE's assistant secretary for environment, safety and health.

Problems at Weapons Plants

Worker health and safety issues at nuclear weapons facilities across the nation pose mounting problems for the Department of Energy. In the first half of the decade, DOE spent $70 million for legal defense of former and current contractors who operated the plants. Here are some key cases:

Hanford Nuclear Reservation in Richland, Wash.: In 1997, the federal Agency for Toxic Substances and Disease Registry concluded that 14,000 people living near Hanford were exposed to enough radiation to put them at risk of thyroid cancer and other diseases. The agency has proposed a $12.9 million fund to pay for medical screening for local residents, but Energy officials have not yet agreed to pay.

Rocky Flats in Colorado: This plant's production of plutonium triggers for nuclear bombs resulted in an epic case of plutonium contamination on the outskirts of Denver. The plant's former manager, Rockwell International Corp., has paid millions of dollars in fines stemming from environmental problems. In April, Rockwell was ordered to pay another $4.1 million based on whistleblower claims that the company lied about environmental problems to boost profits.

Mound Plant in Miamisburg, Ohio: DOE last month agreed to pay millions of dollars for long-term health screening for plant workers, who produced nuclear bomb detonators. Plaintiffs claim they were exposed to radiation hazards without being informed. In one case, urine samples that were collected from workers to measure radiation weren't tested for more than three years.

Fernald Environmental Management Project in Ohio: The plant's 3,500 workers won a $15 million court settlement from DOE in 1995. Most of the money will go for medical screening of workers, who process uranium metal into fuel rods for nuclear reactors. Earlier, a class action suit garnered $78 million for hundreds of homeowners whose property values were diminished by Fernald's contamination.