COLUMN LEFT : The Futility of Nipping at Castro’s Heels : Cuba is shaky enough without needing a putsch from the U.S. radical right.

A fax arrived the other day from an outfit called the Council for Inter- American Security. It was an invitation to take part in an unusual kind of lottery; the idea was to predict the exact day that Fidel Castro would be driven out of power. First prize is a four-day expenses-paid vacation in “liberated Cuba.” Entries must be received by Sept. 30.

There’s been a lot of talk like this of late in conservative circles. Is their excitement well-founded, or is it just another chapter in a 30-year anti-Castro revenge fantasy?

There is no doubt that the Cuban Revolution is in the gravest danger. Although Moscow has renewed--and even increased--its annual trade and aid package with Cuba, recent Soviet statements make it clear that the special relationship is to be phased out. It’s important to recognize what this means. The terms of Cuba’s survival outside the Western financial orbit have been its membership in a strong alternative economic system. But the Soviet Union has now abandoned the pretense of global competition, and Mikhail Gorbachev has made it clear that he sees no future for the Soviet economy outside a single world market, convertible ruble and all.

That is the real significance of the end of the Cold War, and of the West’s victory. And it leads the Soviet Union to conclude that its trade with Cuba is not, as the Cubans have always tried to believe, the microcosm of a new and more generous world economic order. Moscow now admits that its aid to Cuba is what the Americans always said it was--a system of artificial subsidies to underwrite a congenial political system (rather like U.S. support for Puerto Rico, in fact).

Standing at this crossroads, Castro appears to have two options: either open a political dialogue or retreat into autarky. Unhappily, all the signs point in the wrong direction: Under the slogan “Socialism or Death,” Cubans are being told to prepare for a war economy; the recent row over Cubans seeking exile in the Spanish embassy shows that Castro is willing to antagonize even friendly Western governments rather than allow any “antisocial elements” to flee the island; and after a relative relaxation in 1988-89, dissident human-rights activists are again being jailed.

But there is a paradox: Even if Castro were to choose dialogue, with whom would he talk? It always seems to escape Americans that Cubans are not Romanians, passively waiting to shake off a despised tyranny. Castro’s only serious internal threat comes from militant young Communists, who are disgusted by stagnant bureaucracy and closed minds and want to take the revolution back to its roots. Three million Cubans turned out to celebrate May Day this year; where else did that happen?

There are still a handful of principled dissidents on the island who have not been sucked into the vortex of Miami politics. But what could they deliver in negotiations? And how can Castro be expected to talk with exiles who dream openly of turning the island into a dependency of Dade County and have a violent 30-year history of collusion with the CIA?

The only dialogue that matters is with the United States, and flexibility from Castro would mean flexibility from Bush. But after the invasion of Panama and the Nicaraguan election, all the Administration’s rhetoric suggests that Cuba is the next target. The 30-year blockade continues to be enforced in petty and vindictive ways: American companies are now being prevented from upgrading Cuba’s bowling lanes in preparation for the 1991 Pan-American Games.

Last month, the Cuban terrorist Orlando Bosch was released on parole in Miami. He is believed to have planned the 1976 bombing of a Cuban airliner in flight, killing 73 people. There were no visible judicial grounds for his release. On the contrary, it seemed to pander again to the power of the radical right wing of the Republican Party in south Florida--which includes the President’s son, Jeb Bush.

But here is an alternative hypothesis: On issues from taxes to Vietnam, George Bush has been willing to face down his own right wing. Playing out a Cuban end-game on the right’s terms could have fearsome consequences, given the militarization of the island and the degree of popular support for Castro. And Washington can hardly relish the idea of a repeat of the 1980 Mariel boatlift. What if Bush had a secret accord with Gorbachev over Cuba, as Time recently reported was the case over Nicaragua? Its biggest political obstacle would be the Cuba-fixated radical right, who could be shut up only if they were thrown a large enough bone. Orlando Bosch? Stranger things have happened.