Nuclear data show deliberate exposure by U.S.

WASHINGTON -- Shedding a cloak of Cold War secrecy, the Energy Department has disclosed that the United States conducted 204 secret underground nuclear tests over 45 years and deliberately exposed at least 18 Americans to dangerous levels of nuclear material.

Energy Secretary Hazel O'Leary said yesterday's revelations, made possible by the end of the nation's nuclear rivalry with the former Soviet Union, represent the most sweeping declassifying of information in the department's history. She promised additional disclosures as she tries to win new public confidence for the department, which took over the development and manufacture of the nation's nuclear weapon stockpile in 1977.

"We've got to expose the impact of the Cold War, both in terms of its environmental health and safety impacts and also impacts on . . . the psyche of the nation," Ms. O'Leary said. "One of the benefits to openness will be to build public trust."

Ms. O'Leary stressed that the disclosures would not aid Third World countries wishing to develop nuclear weapons. "While we are releasing information, we're not putting other information in the hands of people from terrorist states who could design a very crude bomb and do damage," she said.

Ms. O'Leary declared that she has been "shocked and amazed" at shortcomings in the management of the nation's nuclear weapon complex under Cold War administrations. Among the effects of the department's secretive leadership is an environmental cleanup bill that may reach hundreds of billions of dollars.

Ms. O'Leary said she plans to release more information in June about experiments in which 18 people were injected with plutonium in the 1940s. Those tests were among an estimated 800 various experiments involving more than 600 individuals over the years.