A man claiming to belong to a group called the Nuclear Liberation Front claimed responsibility for a bomb that blew out dozens of windows at a laboratory where nuclear weapons are designed. The bomb, planted beneath a car in a parking lot near the Lawrence Livermore National Laboratory, 40 miles east of San Francisco, exploded Saturday morning. There were no injuries, but the blast destroyed the car and damaged at least three others, created a small crater in the parking lot and scattered debris for 400 yards. Authorities and local anti-nuclear groups said they had never heard of the Nuclear Liberation Front. A man identifying himself as "Oppie" called the Associated Press and said he and his friend the "Plutonium Kid" had carried out the bombing as members of the Oppenheimer Brigade of the Nuclear Liberation Front. The late J. Robert Oppenheimer, an American physicist, was a key figure in the development of the first atomic bomb. The man described the organization as international and said more attacks were planned.