WASHINGTON, July 20 — President Clinton's national security advisor, Samuel R. Berger, inadvertently removed classified national security documents from the National Archives while vetting them in preparation for testimony before the Sept. 11 commission, his lawyers said Monday night. The revelation caused political fallout whose importance was not clear today. Mr. Berger removed at least two slightly different versions of a memo critiquing how the government handled national intelligence and security issues before the millennium celebration in December 1999, as well as personal notes he had taken on classified documents, according to one of Mr. Berger's lawyers, Lanny Breuer. "In...