The Board of Supervisors voted 8-3 this afternoon to reject Mayor Gavin Newsom's proposed ordinance that would make it illegal to sit or lie on public sidewalks during certain hours. ''The case for this legislation simply has not been made,'' said Supervisor David Campos. Defeat was expected, and the mayor already has said that he would use his executive power to put his measure before voters in November. The idea sprang from frustrated residents and merchants in the Haight-Ashbury who are fed up with people congregating in front of their homes and businesses, menacing passersby. Critics, including homeless advocates and...