As some of the passions raised by the Falkland Islands fade with time, Cuba is seeking to use the common interests it found with South America in wartime to forge more solid relations.

In the process, tough talk from Washington that might have increased this island's isolation a year ago is now helping it to recoup some diplomatic losses.

When Cuban officials look at a stern-sounding U.S. Senate resolution that declares the United States is "determined" to contain Cuban subversion by force of arms if necessary, some of them appear almost relieved.

Although seriously worried as always about the threat of military action against their government, the Cubans believe that -- in the aftermath of the Falklands -- hard-line U.S. statements that sound good in North Carolina or Idaho sound aggressive and ugly in Buenos Aires or Caracas.

"It's very good for us that the resolution clarifies the United States' real sentiments," said Deputy Foreign Minister Ricardo Alarcon, after looking over a copy of a militantly anti-Cuba Senate measure sponsored recently by Sen. Steve Symms (R-Idaho).

Interviews with several Latin American and other Western diplomats here suggest Alarcon may be right.

"The drawing together of Cuba and Latin America is important," said one South American diplomat here, speaking of the atmosphere in the region since Washington backed Britain in its successful fight for the Falklands. "But what is most impressive is Latin America's alienation from the United States."

Several South American countries have grown "relatively" closer to Cuba in recent months, the diplomat continued, but he insisted that "the impulse for this is coming from the north, not from the south."

In the face of Washington's threats, Cuban President Fidel Castro has taken a conspicuously moderate approach.

"I believe they the Cubans are hitting a new note," said another Latin diplomat, pointing to Castro's annual July 26 speech celebrating the anniversary of his revolution as "very moderate, without an attack against anyone."

According to various diplomats, Cuba's relations with Ecuador and Peru, which iced over after ugly incidents with dissidents seeking asylum, including the massive occupation of Peru's Embassy in 1980, are showing signs of a thaw.

Argentina's long-standing, businesslike relations with Cuba were growing tense early this year as Buenos Aires sent military advisers to anticommunist governments in Central America. After Cuba's staunch support over the Falklands, however, relations have been smoothed once again, although reports that the advisers had been pulled out could not be confirmed.

Not every development has been positive for Havana. Much-needed trade relations with Brazil, which appeared imminent a year ago, have not materialized; they reportedly have been blocked by conservative members of the Brazilian armed forces.

Although Colombia's newly elected president has made declarations appealing to regional solidarity, no one here suggests that relations between Bogota and Havana have warmed. Colombia, which hosted the Caribbean Games four years ago, declined to send a team to them this month in Havana.

Cuba's greatest diplomatic reward is the new cordiality it has achieved with Venezuela. The rapprochement with Caracas is a crucial test of Cuba's attempt to break, for good, the hemispheric isolation that was almost complete in the 1960s, seemed to wane in the mid-1970s, then started to close in again with the coming of the Reagan administration.

Venezuela's present Christian Social government has been a major U.S. ally in Latin America, generally backing Washington's hard line against leftist revolutionary change in Central America. But Venezuela gave firm backing to Argentina in the Falklands crisis and has moved to distance itself from Reagan administration policies since.

Alarcon described Cuba's new relationship with Venezuela as "a little paradoxical." On a bilateral basis, said the deputy foreign minister, "there are some problems pending that are very complicated," while "in more general Latin American affairs there have been a series of convergences of viewpoint."

"Naturally one thing influences the other," said Alarcon.

After two years of drastically reduced diplomatic representation, Alarcon said, there are now "several indications of the possibility of normalizing relations," and added that "the political will to do so" exists "on both sides."

A well-informed diplomat agreed. "There has been a positive evolution. It is not that relations have normalized, but there is a good environment. Let's say there is good will on the part of both countries."

One of the roughest bilateral questions between the countries concerns the fate of Venezuelans and Cuban exiles accused of blowing up a Cubana airlines passenger flight near Barbados that killed 57 Cubans and 16 other passengers in 1976.

When Venezuelan President Luis Herrera Campins declined in 1980 to change a military court decision acquitting the four men charged, Castro shut down his embassy in Caracas, and Venezuela recalled its ambassador. It is now represented here by a charge d'affaires.

Venezuela did not release the men, however, pending ratification by the Supreme Court. When the two Venezuelans charged in the bombing briefly escaped from jail in Caracas earlier this month, Havana remained silent.

Another complicating factor is the asylum granted by Venezuela's embassy here to about 15 Cubans, some of whom sought refuge behind its iron gates in violent incidents.

The 15 remain trapped and incommunicado, but, according to diplomats here, 127 other Cubans seeking to join their families in Caracas were quietly flown there with Cuba's approval on a Venezuelan charter at the beginning of the month.

But it is on regional issues that Venezuela and Cuba appear to have found new common ground, and their affinity cannot help but undermine Reagan administration policy toward the Caribbean Basin.

A year ago, said Alarcon, Cuba's relations with Venezuela were characterized by "completely opposing views" on Central America's conflicts. Now, however, Alarcon believes "Venezuela is adopting a more careful position toward Central America" and "undoubtedly is one of the factors weighing against U.S. imperialist intervention and in favor of international pluralism."

Alarcon cited the visit of Venezuelan President Herrera Campins to Nicaragua in July just as Washington was pressing to isolate the pro-Cuban Sandinista government.

In addition, Alarcon said, Venezuela has voted with Cuba in the U.N. Special Committee on Decolonization for the independence of Puerto Rico, Caracas has opposed U.S.-backed military maneuvers in the Caribbean and appears ready to enter the Nonaligned Movement, currently presided over by Castro.

Some Latin American envoys here believe that rapprochement between Havana and the capitals of South America may give Castro "breathing space" to moderate his own foreign and even his domestic policies.

One Western diplomat wondered whether the "posturing and rhetoric" that accompanied the Falklands crisis will really have any long-run impact on Cuban relations with the rest of the hemisphere, but Latin diplomats in Havana are convinced that it will. They say the United States will no longer be able to impose revised versions of the Monroe Doctrine on the hemisphere, as both Cuban and Venezuelan officials have accused it of trying to do with such measures as the Symms resolution.

In this new environment, said one senior Latin diplomat, the question of long-term regional security may even hinge on "how you could stabilize the area in a way that would be to the benefit of Cuba, the United States and the Soviet Union."