THE AMERICAN debate about economic connections to embargoed Cuba has produced some modest tentative gains for free trade, thanks mainly to the desire of American farmers to sell crops that are otherwise a drag on the market. But Cuba's poverty and the small size of its economy put their own tight limits on the economic possibilities of an expanding relationship, even as the continuing internal American concern for Cuba's Communist dictatorship limits the political possibilities. Fortunately, there is a better, more promising and more urgent arena of American debate about Cuba: cooperation in drug interdiction.

It should be a natural: Americans know well and detest the scourge of drugs, while Fidel Castro fears the infection of his people by America-bound drugs that, by criminal design or authentic accident, find their way to Cuba. President Castro reported on the recent national day that just in the first half of 1999, 4,539 kilograms of drugs washed up on Cuba's northern coast -- cargo dropped off by airplanes in the Old Bahama Channel and meant to be picked up by speedboats.

The Cuban authorities are promoting a vigorous campaign for cooperation with Americans against drug trafficking. This has alarmed some Americans in Congress and in Miami. They fear that the Cubans will turn the struggle against illegal drugs away from real law enforcement and toward their own political advantage. In this flank of American opinion, there is a deep suspicion that the Castro regime itself participates in and profits from the vile trade.

There is anecdotal evidence to the contrary. In one conspicuous case in which a tanker had been grounded in Cuban waters, the Cubans cooperated amply in discovery, investigation and a subsequent Miami trial. To the continuing dismay of some Americans, Cuban conduct in that episode whetted the appetite of American drug enforcement officials for making cooperation with Havana systematic and routine, not just a matter of occasional opportunity.

The issue of Cuban complicity in the drug trade has yet to be addressed in Washington with the fullness, vigor and publicity that would allow the United States to take Fidel Castro's demonstratively extended anti-drug hand. But the Clinton administration has undertaken an intelligence review; this was reported by Juan Tamayo of the Miami Herald and relayed by President Castro. If Cuba passes a rigorous test of its fitness for pragmatic partnership on this issue, then the United States should explore what can plausibly be done.

Such a development would grant a degree of legitimacy and favor to the Cuban regime; this troubles Miami. But even those Americans for whom this would be not a boon but a bitter pill could presumably share in the satisfactions of limiting some greater part of the flow of drugs across the Caribbean and into the United States. The critics of Clinton administration policy are sensitive to any suggestion that they are putting anti-Castroism over the protection of American citizens, and they should be.