WASHINGTON - The Bush administration has begun designating as secret some information 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 have treated 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 non-profit 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, released Friday, 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 for years kept secret a reclassification program by the CIA, Air Force and other agencies to withdraw thousands of records from public shelves.

One month after the 9/11 terrorist attacks, then-Attorney General John Ashcroft instructed federal agencies to be more mindful of national security when deciding whether to publicly release documents under the Freedom of Information Act.

Maj. Patrick Ryder, a Pentagon spokesman, said officials strive to properly apply rules governing what should be classified and are researching why the missile information cited in the archive report was blacked out.