CUBA REFROZEN

Cuba's downing of-the Brothers to the Rescue planes halted the thaw in relations that had seemed slow but inexorable. That suits Fidel Castr o perfectly. Anti-Americanism hitched to a very Cuban sense of doomed defiance is the only sentiment he has going for him now that faith in socialism is dead and his regime is peddling tried-and-failed solution s for the ramshackle economy. Ironically, Castro's sovereignty fetish has driven Cubans into dependence on Miami, as well as into poverty an d crime. But the Maximum Leader, who has outlasted eight U.S. presiden ts, is a wily tactician, A post-Castro Cuba does not seem imminent.