SIX YOUNG MEN were arrested in two bombings and a fire at McChord Air Force Base, Wash., that apparently were acts of retaliation, not terrorism, authorities said . . . A MINIBUS plunged off a bridge in South Africa's central Orange Free State province early Tuesday, killing 19 people, state-run radio reported . . . A HONG KONG immigration official said Tuesday that 111 boat people would be freed on bail, 24 hours after authorities defied a judge's order releasing them from 18 months of what he ruled was illegal detention . . . FOUR SOUTHERN CALIFORNIANS were killed Monday when their single-engine plane crashed into a hillside while taking off from the Aspen, Colo., airport.