Confusion reigns in Washington as to what action the Reagan administration might be contemplating against Cuba and Nicaragua. The administration systematically has been building a case for American concern over the growth of Nicaragua's military forces and Cuba's reported use of Nicaraguan territory to ship arms to El Salvador. But when it comes to remedying the situation, the administration seems to speak with many voices.
At one point recently, White House counselor Edwin Meese III was saying that a naval blockade of Nicaragua might become a subject for discussion by policymakers.
In the past, Secretary of State Alexander M. Haig Jr. has expressed concern about what he calls the ''totalitarianization'' of Nicaragua. But now he has come out with a softer line, pointing to the ''many strong forces for pluralism'' in Nicaragua. The public statements may amount to calculated ambiguity. If nothing else, they are part of a war of words now being waged between the Reagan administration and its Caribbean opponents.
The latest word on Nicaragua came from Secretary Haig. He told reporters at a meeting on the Caribbean island of St. Lucia on Dec. 2 that it was still too early to say that Nicaragua had moved irreversibly toward totalitarianism. Haig reiterated his concern over Nicaragua's military buildup. But he also said that the United States was not going to be the ''exclusive policeman'' of the hemisphere. He repeated President Reagan's assertion that the US had ''no plans at this time'' for the use of military forces anywhere in the world.
A State Department official said on Dec. 3 that the US was far from launching any form of military intervention against Nicaragua, either in the form of a naval blockade or in the form of a more direct attack on that central American nation.
US intelligence officers are said to be most concerned at the moment about the possibility that Nicaragua will acquire Soviet-built MIG fighter planes from Cuba. Some months ago, US officials reported that the Nicaraguans were lengthening several of their airfield runways, apparently in preparation for such planes.
But Haig, who originally was viewed in Washington as an advocate of strong action against Cuba and Nicaragua, is now increasingly viewed as the man in the middle, trying to avoid extremes.
Meanwhile, military experts from the Defense Department have pointed out that military action against a heavily armed Cuba would require reducing American military forces elsewhere and might in the end prove ineffective.