Part of a college campus was evacuated because of a bomb threat, the latest in a series of incidents that started with two fire bombs placed in Concord, N.H., libraries last week. An anonymous call warned that three bombs had been placed on the campus of the New Hampshire Technical Institute, said Mike Moffett, the school's public information officer. About a dozen buildings were evacuated, including a state police training building and the Christa McAuliffe Planetarium. A police bomb squad gave the all-clear after about 2 1/2 hours of searching turned up no evidence of a bomb. Two pipe bombs were found Tuesday at the city and state libraries. One bomb started a fire at the city library, but no one was injured. About 1,200 students attend the technical college and 400 live on campus.