CUBA . . . U.S. READY TO BLOCK EXODUS

President Clinton would invoke emergency powers to confiscate any vessels trying to rescue would-be Cuban emigres at sea should Fidel Castro's threatened mass boat lift become a reality. But State Department officials said they're reassured by signs that Florida's Cuban exile community won't rush to pick up fleeing boats, as they did during the 1980 Mariel exodus. This time, the exiles say, helping the dissidents leave would ease the pressure on Castro to reform his system.