RELEASED. Ricardo Montero Duque, 60, a battalion commander in the 1961 U.S.-supported Bay of Pigs invasion, which sought to overthrow Fidel Castro, and the second-to-last prisoner being held; after serving 25 years of a 30- year sentence; from a Havana prison. Montero Duque flew to Florida with aides of Senator Edward Kennedy; with others, Kennedy was credited with effecting the release. The prospects for the remaining prisoner, Ramon Conte Hernandez, are unknown.