FIDEL CASTRO CONTINUES to lavish on American visitors what is still one of Cuba's principal assets: his time. The most recent recipient was Sen. Frank Church, on whom the Cuban leader bestowed several days. They seem to have struck a fair bargain. In effect, Mr. Castro decided to let the Cuban families of some 80 American citizens leave Cuba, in return for the respectability conferred by the Church party. He also released two Americans whose boat had recently been captured. Such gestures cost Havana little. They provide a substantial return in "humanitarian" image. And, of course, they transform the lives of the individuals involved.

Sen. Church is a good man to have gone to Cuba. He understands foreign policy and, though personally of a liberal outlook and also the man who disclosed the CIA's attempts to kill Mr. Castro, he is politically in touch with the conservatives who oppose Cuba's Communist regime. He warned his Cuban host that, though small steps are possible and desirable, normalization is a long way off. This is sound advice. Things are moving: Cuba is about to open, on a reciprocal basis, an "interests section" in Washington. But the agreements reached so far touch mainly areas of convenience (fishing, hijacking). Broad support is still lacking here - and perhaps also in Cuba - for full and friendly ties.

In fact, the two countries may be on the verge of running out of easy gestures. Mr. Castro could release the 20 or so Americans in Cuban jails. Mr. Carter could lift the trade embargo partially to permit the sale of food and medicine. Then would come the hard part: a range of steps that would require an American decision to accept the Cuban revolution as authentic and permanent and a Cuban decision once again to act primarily as a member of the inter-American community. Only these steps would lead to a stable and productive long-term relationship.

So long as Cuba remains a treaty partner of the Soviet Union and deploys troops across Africa, it is idle to suggest that Fidel Castro is close to returning to the inter-American fold. But is the United States prepared to extend Havana the economic and political concessions that would signify acceptance of the Cuban revolution? A new Potomac Associates survey raises serious doubst. The American public, it says, "is receptive in the abstract to engaging the Cubans in negotiations about a diplomatic reapprochment, but wants to do so only on terms likely to be unacceptable to Havana." Some Americans see reconciliation as a test of their own maturity but most see it as a process in which benefits flow largely from north to south. Therefore, in the public view, major concessions - in foreign policy and domestic practice - must come from Cuba. It is probably just as well that in neither Washington nor Havana is the improvement of relations the No. 1 priority, for in neither place is that likely to happen soon.