The National Assn. of Broadcasters--some 6,000 radio and television stations strong--is mounting a fight against a U.S. Senate effort to revive the Fairness Doctrine and impose a fee on station license transfers. An association mailing described the Senate Commerce Committee's approval of a fairness doctrine and transfer fee amendment as "the congressional equivalent of a kangaroo court." Congress earlier this year passed legislation to write into law the 38-year-old doctrine, which requires broadcasters to air divergent views on controversial issues. President Reagan vetoed the measure, and the Federal Communications Commission scrapped the policy in August.