U.N. Secretary General Javier Perez de Cuellar has decided on rules widening the access to files on 40,000 alleged war criminals and witnesses compiled by a World War II commission, a spokesman said. The rules would permit U.N. member nations to authorize their own nationals--researchers, writers, reporters and historians--to view individual files. The ruling was considered a victory for Israel and Jewish groups, who had campaigned for greater access to the files. An Israeli spokesman said the decision is "tremendously important both for justice . . . and to counter those who say the Holocaust never happened."