Doctors disputed a claim at a recent Senate hearing that an AIDS virus infection among West German prostitutes has reached major proportions and has been transmitted to American GIs. Dr. James J. James, stationed at the U.S. Army Hospital in Berlin, and two colleagues said a far larger percentage of female intravenous drug users test positive for exposure to the virus believed to cause AIDS. But researcher William A. Haseltine told the Senate hearing last September that between 20% and 50% of unregistered prostitutes are infected with the AIDS virus and 5% of U.S. soldiers reporting to venereal disease clinics in Berlin are also infected. In Atlanta, two organizations representing American prostitutes said they will cooperate with the Centers for Disease Control in a federal study seeking to determine whether prostitutes are spreading AIDS to heterosexuals. The leaders said they welcomed the study because AIDS threatens their lives and their livelihoods.