Government agencies inadvertently declassified 14,890 pages of sensitive nuclear weapons information from the 1950s and 1960s that in at least one case were accessed by an outside researcher, according to a recent Department of Energy report to Congress.

In a cover letter, Energy Secretary Bill Richardson said he recognized the "gravity" of releasing classified information about even the nation's earliest nuclear weapons, which the report said could "provide useful design parameters to emerging proliferant nations and to terrorist groups."

The report, an unclassified summary of a longer classified document, said the 14,890 pages of DOE documents inadvertently declassified by other agencies contained "nuclear weapon design information from the test results of a specified nuclear test program" and "records covering nuclear weapons utilization information such as yields of specified weapons and deployment and storage locations." All have now been withdrawn from public access.

"Compelling evidence," the report said, exists in only one case showing that a researcher "obtained and used" information "related to the deployment of nuclear weapons in a foreign country in the early 1950s," not information pertaining to weapons design.

Congress ordered the report in 1998 after Sen. Jon Kyl (Ariz.) and other Senate Republicans took steps to modify President Clinton's 1995 executive order mandating automatic declassification of historic documents after 25 years, fearing that just such nuclear secrets would be revealed in the process.

In addition to ordering an investigation of all inadvertent disclosures of classified nuclear weapons data from 1995 to 1998, Congress also required all agencies to begin a page-by-page review of historic documents declassified under Clinton's executive order.

The Energy Department report on inadvertent disclosures, dated August 1999, was not sent to the Senate Armed Services Committee until late last year. It was publicly released last week and posted on the Internet by the Federation of American Scientists' Project on Government Secrecy, which closely monitors declassification issues.

Steven Aftergood, the project's director and a strong declassification advocate, called the inadvertent declassification "disturbing" and said no one ever "wants sensitive nuclear weapons information to be carelessly disseminated."

But he questioned the true sensitivity of classified data older than 25 years and said even the weapons design information probably does not pose serious concerns with regard to nuclear weapons proliferation.

"Information about nuclear weapons design is no longer the main barrier to weapons proliferation," he said. "The main barrier is access to fissible material."

One senior Energy Department official, who asked not to be identified, argued that the inadvertent disclosure of even old weapons design data, despite the availability of warhead design on the Internet, is serious.

"When you get a document that is an official U.S. government document out of one of our national labs, the credibility of that information is far different from some stuff that may be on the Internet," the official said. "I'm very glad we found it and pulled it back."

The official said further discoveries of inadvertently declassified nuclear weapons data are highly likely because DOE's review to date has only encompassed 948,000 pages considered the most likely to contain nuclear secrets. More than 600 million pages of historic records have been declassified so far under Clinton's executive order. Government agencies are declassifying more than 100 million pages a year.