FIDEL CASTRO over the years has managed to substitute a series of sleight-of-hand tricks for the serious dialogue that alone would permit normal relations to be restored between the United States and Cuba. His sudden release of 30-odd American prisoners fits in this category. From a certain Cuban point of view the gesture is a success: it produced headlines and revived the notion that Mr. Castro may be a nice guy, maybe worth dealing with, after all. But wait a minute.The prisoners were never much more than a card waiting to be played. In that sense, their release is no more substantive than other recent Castro gestures, like returning two Cuban refugees who had hijacked an American airliner and permitting Cubans marooned in the American diplomatic mission in Havana to go home. These gestures amount to cleaning up the debris of crockery broken by Fidel Castro himself.

It merely invites confusion and later frustration to take one's mind off what are, in 1980, the reasons that tensions between the United States and Cuba persist. These are not the same as the reasons that tensions existed 10 or 20 years ago. Jimmy Carter, in 1977, gave every sign that he was ready to accept the legitimacy and permanence of the Castro regime -- the chief block on the American side -- and to establish normal ties. Small but valuable steps were taken in both directions. Americans became increasingly convinced, however, that in Africa and elsewhere Mr. Castro was lending himself to a concerted Kremlin strategy to test the Soviet Union's developing military reach. Some part of this American concern may have been overwrought, but a larger part was reasonable.Thus did Mr. Castro dissipate the best chance he has had in 20 years to make up with the United States.

It is speculated now that Mr. Castro fears the election of Ronald Reagan, whom he takes to be demonstrably less ready than Jimmy Carter to accept socialism 90 miles from Florida. Whether his apprehension is justified is to us a question. In any event, we doubt that it will make all that much difference to Havana who is the next American president. There is a consensus in the United States against normalizing relations with a Cuban regime that acts as an outrider for Moscow. Mr. Castro cannot expect to enjoy trade and the other advantages of normal ties with the United States and to support foreign "revolutions" against "American imperialism" at the same time.