Energy Secretary Bill Richardson ordered an immediate investigation yesterday into reports that thousands of unsuspecting employees at a Kentucky uranium plant were exposed on the job to cancer-causing plutonium.

Richardson said he would meet with workers at the Paducah Gaseous Diffusion Plant and would request a National Academy of Sciences study to probe the links between worker illnesses and exposure to radioactive materials that occurred over decades at the federally owned plant.

He also called for expanding a newly created program to bring health screening and medical treatment to thousands of workers who may have been put in harm's way at Paducah and similar facilities that were part of the government's nuclear weapons complex.

"I have long maintained that we must correct the sins of the past by compensating workers who have been medically damaged," Richardson said in an interview. "I don't want this to be known as the department of excuses for not dealing with workers who have been harmed."

His remarks came after The Washington Post reported that workers at the Paducah plant had been unwittingly exposed to plutonium and other radioactive metals that entered the plant over decades in shipments of used uranium from military nuclear reactor fuel. The report was based in part on sealed court documents filed as part of a lawsuit by workers and an environmental group, the Natural Resources Defense Council. The suit alleges that government contractors concealed evidence of the exposure for decades while allowing plutonium and other hazards to spread into the environment.

The workers also allege that former plant managers allowed contaminated waste to be dumped into a state-owned wildlife area and a landfill not licensed for hazardous waste. They further contend that radioactively contaminated gold and other valuable metals may have been shipped out of the plant without being properly tested.

Thomas Cochran, a nuclear expert with the NRDC who reviewed conditions at the plant, said health and safety practices there were the worst "outside the former Soviet Union." Former plant operators had not been served with the suit and declined to comment. The whistleblowers and their Washington attorney, Joseph Egan, said they also could not comment because of the judge's seal on the case.

Energy officials sent a team to Paducah for an initial probe after the documents were first filed in June, Richardson confirmed. "They did not uncover any imminent threats . . . but we are continuing to investigate these concerns," Richardson said.

The expanded investigation he announced yesterday would seek to uncover "what actually occurred, who was responsible and what must be done to assure that it never happens again," he said.

Among the specific measures:

Top Energy Department officials will be dispatched to Paducah this week to check compliance with environmental and safety regulations. The agency's Office of General Counsel will assess whether former contractors, including Lockheed Martin Corp. or Union Carbide Corp., had fulfilled their responsibilities to protect workers and the environment.

Besides the health study by the National Academy of Sciences' Institute of Medicine, the Energy Department will institute a medical surveillance and screening program for employees. A screening of former Paducah workers is just beginning as part of the Former Worker Program, a congressionally ordered study of past exposures of employees in the U.S. nuclear complex.

The department's fiscal 2000 budget request will be reassessed and revised as necessary to include money to probe and rectify environmental and health concerns at the government's uranium enrichment plants.

Richardson will ask the White House to expand a newly created program to provide millions of dollars in medical screening and other benefits to Energy Department workers who were exposed to beryllium, a highly toxic metal used in nuclear weapons. "These actions are warranted given the concerns raised . . . and I will not rest until these issues are fully dealt with and any injured workers are fairly compensated," Richardson said.

Paducah workers were exposed to plutonium through shipments of contaminated uranium that arrived at the plant from 1953 to 1976, a period when national security priorities often surmounted concerns over risks to workers and the environment. The plutonium shipments stopped, but contaminants remain spattered over hundreds of acres of buildings and grounds. Workers did not learn of the problems until at least 1990, and some contend they were never told.

The U.S. Enrichment Corp., a government-chartered private corporation that took over management of the plant this year, contends that all significantly contaminated areas have been cleaned up or marked with warning signs.

Although no comprehensive study of worker medical histories has been conducted, current and former workers at the plant have linked past exposures to a string of cancers and other diseases.

Richardson said although many of the exposures at Paducah were historical, the government bears responsibilities for those who may have been injured.

"Even though it was the 1950s and everyone was gung-ho," he said, "it doesn't mean that you can forget about workers who have been made sick."