CUBA SAYS that the Bahamian patrol boat its MiGs sank on Saturday in Bahamian territorial waters was first thought to be a "pirate boat." What a flimsy excuse. There was piracy in this incident, all right, but it was entirely Cuba's. The Bahamas maintains correct relations with Havana and has kept aloof from the latest refugee crisis. Its plainly marked, easily identifiable 102-foot patrol boat had picked up two Cuban fishing boats for poaching (a number of other Cuban boats and American boats have been similary detained in recent years). In daylight, the Cuban jets blew up the ship and, for good measure, machine-gunned the crew in the water. When survivors reached land, Cuban planes buzzed them and a helicopter actually landed on Bahamian soil.

The incident suggests Cuba's contempt for its law-abiding neighbors -- and something more. It suggests a puzzling erraticism and instability on the part of Fidel Castro. He had the option of saying that an air squadron had gotten trigger-happy. Even while offering "sincere regrets" later, he chose to affirm that the squadron was flying under official orders. Why would Cuba want to pick a fight with one of its quietest neighbors? At a moment when hemispheric opinion against Cuba is inflamed on the refugee issue, why would Mr. Castro conduct a raid certain to underline again the rogue quality of his regime, and certain, too, to play into the hands of those who would like to legitimize the use of force against Cuba? It is hard to answer questions like these about a communist dictatorship without wondering whether there are not hidden strains within the regime and perhaps even between elements of the regime and its Soviet patrons.

In any event, Cuba's quickness to use force against an unoffending neighboring state, and to assume openly the role often attributed to it of being a menace to peace, does raise the temperature of the whole region. The shootup underscores the gap between Cuba's methods and purposes and those of other states in the hemisphere. Piracy is the right word.