The National Archives started a formal investigation Wednesday into the loss of a file of Judge John G. Roberts Jr.'s papers on affirmative action from the Ronald Reagan Presidential Library. Senate Democrats, preparing for hearings on Judge Roberts's nomination to the Supreme Court, had asked Tuesday for the investigation. They noted that Bush administration officials had reviewed the files in July before they went missing.

Members of the archives staff have said the loss of the file was their own clerical error, and they have already made public a facsimile of the file's contents reconstructed from other records. The archives said Wednesday that Reagan library staff members believed that the other records and computer databases had enabled them to reconstruct everything in the file independently.