ByJames Nelson GoodsellJames Nelson Goodsell is the Monitor's Latin America correspondent. For more than a generation, since 1959, seven different United States administrations have struggled with ''the Cuban threat.'' Each has had its own problems with Cuba and its mercurial, but very durable leader, Fidel Castro. But each administration has somehow failed to evolve a workable Cuban policy. The reason for this failure, says Wayne Smith, the former head of the US interests section in Cuba, is ''in large part because our policymakers have not dealt with the problem as it is.'' In his able forward to Carla Anne Robbins's equally able ''The Cuban Threat,'' Smith suggests that ''our policy should be informed by a realistic appraisal of Cuban intentions and capabilities.'' A good place to begin such an appraisal is Ms. Robbins's book. Without minimizing the ability of Dr. Castro to embark on ventures that go against much that Washington regards as important, she says flatly that the time has come for the US to stop fixating on the Cuban threat. In the first place, Washington's approach to Cuba over the past 20 years simply has not worked. ''After two decades of containing the Cuban threat,'' she writes, ''the Castro government is still in power and today has an international reach greater than many European governments.'' She also notes that most US allies maintain ties with Cuba and do business with the island. Only governments like that of Chile's autocratic Pinochet regime go along with ''Washington's perception of the Cuban threat.'' Is there a Cuban threat? Decidedly, yes, Ms. Robbins writes. But it is hardly what most North Americans believe. ''The threat has never been military,'' she comments. Rather it is ''symbolic . . . a threat to our hegemony, to our ability to impose complete agreement in 'our' hemisphere.'' Not all readers will agree with this assessment. What of Cuba's role in Africa? Its efforts to topple governments in the Western Hemisphere? Ms. Robbins takes these into account. To be sure, she says, the Cuban presence in Africa ''has been the source of grave concern to Washington.'' But despite the troop presence, Cuba was unable to turn Angola into a Cuban pawn, much less a Soviet pawn. And as far as Ethiopia is concerned, Cuba has had even less success than in Angola. These points are debatable. Yet the view that Cuba would not be in Africa if it did not want to be there is increasingly being accepted by Cubanologists. Here at home in the Western Hemisphere, Ms. Robbins writes that, while Cuba has ''been able to exercise the greatest influence in Nicaragua,'' the Castro advice to the Nicaraguans ''continues to be remarkably moderate.'' The Sandinistas have been encouraged not to break with Washington, to work for a truly mixed economy, and to embrace political pluralism. Whether the Sandinistas have listened is another matter. The recent visit to Nicaragua of the commission headed by former Secretary of State Henry A. Kissinger suggests that the Sandinistas are taking an increasingly doctrinaire leftist position. There also can be little doubt that they are more hardline, less flexible in their relations with the US. The point that Ms. Robbins makes is that the US simply must pause and take a fresh appraisal of its Cuba policy. The US also needs to look at the Cuba-US imbroglio from a Cuban perspective, looking back over what she terms ''twenty-two years of unremitting American hostility.'' Her book is a good place to begin.