The Bush administration has begun designating as secret some information that the government long provided even to its enemy the former Soviet Union: the numbers of strategic weapons in the U.S. nuclear arsenal during the Cold War.

The Pentagon and the Department of Energy are treating as national security secrets the historical totals of Minuteman, Titan II and other missiles, blacking out the information on previously public documents, according to a new report by the National Security Archive. The archive is a nonprofit research library housed at George Washington University.

"It would be difficult to find more dramatic examples of unjustifiable secrecy than these decisions to classify the numbers of U.S. strategic weapons," wrote William Burr, a senior analyst at the archive who compiled the report. " . . . The Pentagon is now trying to keep secret numbers of strategic weapons that have never been classified before."

The report comes at a time when the Bush administration's penchant for government secrecy has troubled researchers and bred controversy over agency efforts to withhold even seemingly innocuous information. The National Archives was embroiled in scandal during the spring when it was disclosed that the agency had for years kept secret a reclassification program under which the CIA, the Air Force and other agencies removed thousands of records from public shelves.