The shooting death of a leading Haitian dissident last night jolted Haiti back to the forefront of U.S. and international agendas. The Rev. Jean-Marie Vincent -- a close friend of Jean-Bertrand Aristide who threw his body in front of machete-wielding attackers in 1989 to protect the now exiled president -- was shot and killed by gunmen suspected of being part of the military government. There was no indication why Vincent was slain. He was a peasant-rights movement leader, but he had made no political appearances since Aristide's 1991 ouster. In Washington, State Department spokesman Mike McCurry denounced the killing, and rejected speculation the Clinton Administration would delay considering a Haiti invasion until it had handled the Cuban crisis.