While continuing its support for leftist revolutionaries in Central America, Cuba is strenuously pursuing a strategy of improving political, diplomatic and economic ties with key Western European and Latin American states in a bid to intensify opposition to U.S. actions in El Salvador and Nicaragua.

By consistently supporting calls for negotiated settlements of the region's conflicts, Cuba is attempting to place itself in a mainstream of western opinion on Central America that ultimately could force the Reagan administration to back down from its own increasingly hard-line policies and opposition to such talks.

In a larger sense, however, the Cubans appear to hope that U.S. Latin American policy in general--and a perceived shift in international attention from what Cuba is doing to what Washington is doing--will lessen Cuba's overall isolation from the West.

The policy already has shown signs of paying off, according to a number of Latin American and European diplomats here. Following Cuba's strong support for Argentina during the Falklands War, relations between the two "have never been better," according to one informed diplomat.

Noting that the two countries have upgraded their diplomatic staffing in each other's capitals and signed a broad range of commercial agreements during the past year, he called the Falklands "a miracle for Cuba." According to this source, Cuba has assured Argentina that it will no longer have anything to do with leftist guerrillas operating in that South American country, and Argentina has assured Cuba that it has withdrawn the trainers it sent to instruct anti-Nicaraguan guerrillas in Honduras.

Perhaps more significantly, Cuban efforts to move closer to Western Europe, targeted primarily at France, Spain, Sweden and to some extent West Germany, have brought results. Following a visit here last October by Regis Debray, French President Francois Mitterrand's adviser on Latin America, Cuba and France began a series of cultural and economic exchanges that will culminate in a scheduled trip here by French Foreign Minister Claude Cheysson in August.

According to informed European sources, Cheysson is expected to firm up plans for a visit by Cuban President Fidel Castro to Paris within the next year, a plum long sought by Havana.

"We have a level of dialogue we never had before" with the Cubans, one European diplomat said. "We can talk frankly about anything. They supply us on an almost daily basis with information from Central America."

Both the Latin Americans and the Europeans said they were under no illusions that long-term Cuban goals have changed. Cuban "support for negotiations in Central America is always partly tactical," a diplomat said.

European diplomats here say they have made it clear to Cuba that whatever new closeness may evolve between them, they have no plans to change their overall global view of Cuba as a Soviet surrogate, nor to go beyond a certain point in direct opposition to the United States in what is considered the U.S. sphere of influence.

But several Europeans said Cuba has made a correct assessment of both the desire of their governments for a political rather than military solution and their increasing distance from U.S. policy.

The Cuban belief that Washington is fighting a losing political and public relations battle on Central America at home and abroad was repeated over and over again in interviews during the past week with several high-level Cuban officials, including Vice President Carlos Rafael Rodriguez.

At the same time, in what amounts to a Cuban version of the "two-track policy" of simultaneous military pressure and movement toward negotiations reportedly advocated for Washington by Assistant Secretary of State Thomas O. Enders before he was replaced last week, the Cubans also believe they hold a strong military card.

Barring direct U.S. military intervention, which they say will fail because of domestic and international "outrage," the Cubans see the military position of the Central American left--particularly El Salvador's guerrillas--as growing strong.

The Cubans repeatedly insist that they want a negotiated solution in Central America, and point to their public support of international initiatives in that direction as proof. They say their reasons are moral and ideological--to prevent more bloodshed and to allow the socialist regimes they see as inevitable to develop in evenly paced, viable ways.

Failure to begin negotiations soon, Rodriguez warned, will "accelerate" the "transformation" to nonpluralistic socialism by lessening the influence leftist moderates have in their coalitions with militaristic guerrillas.

Right now, said Vice Foreign Minister Ricardo Alarcon, the Salvadoran guerrilla coalition "is not proposing a regime that would prohibit other sectors, which would have to be excluded from a purely military perspective," such as the political parties and armed forces now governing El Salvador.

"If there is a military victory," Alarcon said, "the ones who win with guns would take control."

"We want negotiations," Rodriguez said. "We have said it. The guerrillas have said it." Reflecting Cuban confidence in guerrilla military capabilities, he added, "The negotiations being sought by France, Mexico and other Latin American countries are not negotiations that would submit a guerrilla movement, which has certain popular support and is carrying out successful military actions, to the government."

Talks limited to elections, as proposed by the administration and the Salvadoran government, "are not unconditional negotiations" as proposed by the guerrillas, he said, but an unacceptable call for "unconditional surrender."

Among other points made by the Cubans concerning Central America:

Both Rodriguez and Alarcon repeated Cuban insistence that Havana stopped a regular supply of arms to Salvadoran guerrillas approximately two years ago. They called on Washington to "show us the proof" that arms continue to flow to El Salvador from Cuba through Nicaragua.

Alarcon acknowledged that U.S. efforts to monitor and intercept a flow of arms into El Salvador made such supplies "not possible right now."

But, he insisted, the guerrillas "don't need it . . . they have their own methods" of obtaining arms. "We don't accept the rationale that we shouldn't do it from an ethical point of view," he said. "By saying we are not sending arms we are not trying to make a gesture or a compromise."

He said the Salvadorans "don't have to look outside" at the moment for anything other than "things like plasma, medicine, some special equipment they may lack. I'm not saying they are not buying things in a store in Brooklyn. I'm saying that the 'flow of arms' " described by the administration "does not exist."

Rodriguez denied Reagan administration assertions that Cuba has as many as 2,000 military advisers, as well as 6,000 militarily trained teachers, doctors and other workers in Nicaragua. "There are several dozen" Cuban military, intelligence and security advisers in Nicaragua, he said. "I repeat, several dozen. Not many dozen." He said that this figure has been relatively constant since Cubans first arrived in Nicaragua following the Sandinista victory in July 1979.

As for the overall total of Cubans, he said, "The total is much fewer than 8,000 . . . the teachers are teaching, the doctors practicing medicine, the road builders building roads."

According to Education Minister Jose Ramon Fernandez, who also is chairman of the Council of Ministers of the Cuban Communist Party Central Committee, Cuba was so enraged at charges by then-secretary of state Alexander M. Haig Jr. in 1981 that supposed Cuban teachers in Nicaragua were actually military personnel that it compiled its own defense documents.

During an interview, Fernandez pulled out a two-foot-tall stack of books in which he said had been listed the names, addresses, training and most recent job in Cuba of every civilian who volunteered for duty in Nicaragua. Attached to each listing was a photograph of the "teacher" in question. "We were ready for the debate," Fernandez said. "But it never came."

* The Cubans declined comment on administration reports that they trained at least 20 Honduran leftists last year and currently are training 16 more to be infiltrated back into that country. "They have such precise numbers," Rodriguez said. "I don't know" if the reports are true, he said, noting that such small groups could "hardly be a threat."

Rodriguez said he "does not think" Cuba is directly aiding the left in Costa Rica, as the administration has charged. He indicated that Costa Rica should be presumed exempted from Cuban interference because ways to peaceful change were open there.

* The vice president acknowledged U.S. reports that Cuba has had a leading role in unifying guerrilla forces in Nicaragua, El Salvador and Honduras. "Cuba, and Fidel personally," he said, "have brought together[the guerrilla] forces."

"If guerrilla movements are going to make transformations . . . it is absurd that they have similar goals and tactics yet are divided" among themselves. Their unity, Rodriguez said, "means less loss of blood, less destruction. It accelerates the victory and permits necessary democratic changes to occur more rapidly."

* Referring to a series of charges against Cuba that came out of Washington last week, Rodriguez acknowledged that 400 Cuban marines have been practicing amphibious assault landings on a beach near the port of Mariel. A U.S. specialist was quoted in news reports as saying this was an "important development" indicating a new Cuban threat to nearby Caribbean islands.

Rodriguez described the amphibious assault practice as defensive. "To learn to repulse an invasion, you have to learn how invasions are done," he said.