The National Archives signed a secret agreement in 2001 with the Central Intelligence Agency permitting the spy agency to withdraw from public access records it considered to have been improperly declassified, the head of the archives, Allen Weinstein, disclosed on Monday. Mr. Weinstein, who began work as archivist of the United States last year, said he learned of the agreement with the C.I.A. on Thursday and was putting a stop to such secret reclassification arrangements, which he described as incompatible with the mission of the archives. The disclosure of the secret agreements provides at least a partial explanation for the removal since 1999 of more than 55,000 pages of historical documents from access to researchers at the archives. The removal of documents, including many dating to the 1950's, was discovered by a group of historians this year and reported by The New York Times in February. In a brief interview, Mr. Weinstein said he was particularly disturbed that the archives had agreed not to tell researchers why documents were unavailable. The C.I.A. agreement said archives employees would not attribute to C.I.A. any part of the review or the withholding of documents."

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