It is difficult to walk along Fifth Avenue, Havana's embassy row. Barricades on the sidewalk and stern-faced soldiers armed with Kalashnikov automatic rifles force the pedestrian to detour away from embassy gates.

The soldiers are particularly gruff outside the Venezuelan Embassy, where 16 Cubans have taken asylum, and only two diplomats are present. Cuban officials say the asylum-seekers will "rot" there. Nearby, the old Peruvian Embassy, where last year 10,000 Cubans crowded into the garden in a bid for freedom that began the Mariel exodus, is now a museum commemorating the march staged to repudiate their action. The current minimal Peruvian diplomatic staff has moved to other quarters.

Costa Rica's consular offices are closed, the Colombian Embassy is shut down and Ecuador's embassy is manned by a skeleton staff.

Cuba now finds itself more diplomatically isolated from the rest of Latin America than at any time since the early 1970s, and there are many who say Cuba brought this situation on itself through high-handed dealings with embassies that took in asylum seekers, by helping revolutionary movements in some countries and undiplomatically insulting others.

But the Cuban government sees the glacial chill settling over their relations with much of the continent as a direct result of the new cold war promoted by the Reagan administration in Washington.

"The United States is working frenetically to isolate Cuba politically in the Caribbean area," said Cuban Vice President Carlos Rafael Rodriguez. "They have acted systematically around the governments with which conflicts or elements of conflict have arisen, to take advantage of that with the objective of there being breaks in relations. The conflicts turn into unsalvageable conflicts and the elements of conflict turn into conflicts."

Rodriguez said: "I couldn't offer any evidence that the State Department or President Reagan or other forces have been talking, but we perceive it, that there has been an evident influence, an evident intent to push in this area. We know only too well how they always manage their Latin American policy."

Still Rodriguez and other officials suggest that after some very tough times this spring and summer, relations with several of the "problematic" Latin American countries are once again improving.

In the 20 years since every Latin American country except Mexico broke with Havana, through isolation, relative detente in the 1970s and a new freeze in the past year, Washington's example and sometimes its arm-twisting, along with Cuba's own actions, have created a complex collection of hemispheric relationships.

"We are in the game -- the Caribbean game," said Clara Nieto de Ponce de Leon, Colombia's ambassador to Cuba from 1977 to 1980, in a recent Bogota interview. "And the Caribbean game is to isolate Cuba. We are not the ones who started the game. We are not the brains of the game. But we are in the game because the people who hold power are on that side."

Each country plays the game differently and for different reasons.

Mexico hardly plays the game at all. It never broke relations with Cuba, and especially over the last year its leaders repeatedly have expressed their friendship for the government of President Fidel Castro, both in words and such concrete acts as aid to Cuba's petroleum industry. When Castro has been under diplomatic pressure, especially from the United States, Mexican President Jose Lopez Portillo has made it clear that he remains a Cuban ally on the world scene even though the Cuban and Mexican political systems have little in common.

The only public rebuff Castro has received from Mexico recently is Lopez Portillo's decision -- apparently under U.S. pressure -- not to invite him to the North-South summit in Cancun, Mexico, next month.

Argentina has one of the most rabidly anticommunist governments in the hemisphere, but it does not play the isolation game. It maintains substantial commercial and diplomatic ties with Havana. Although Brazil's conservative military government is leery of any formal contact with Castro, Brazilian business sources say it has given its tacit blessing to large-scale trade agreements now under discussion.

Last spring one of the the most detailed condemnations of Cuba's recent actions came from Panama, whose leader, the late Omar Torrijos, considered himself a close friend of Castro. An article in the government newspaper La Republica, that reportedly reflected Torrijos's views,accused Castro of endangering regional peace, maintaining an "excessive presence" in Nicaragua, frustrating dialogue in Central America by promoting armed insurrection in El Salvador and elsewhere, and giving the Reagan administration an excuse for greater intervention in Latin America.

But diplomatic relations continue between Havana and Panama and have even improved since the death of Torrijos in July, according to Cuban officials.

Colombia, one of the nations with the most difficult history of relations with Havana, suspended full diplomatic relations on March 23 charging that Cuba had trained Colombian antigovernment guerrillas. It based its accusations on a statement by a wounded 18-year-old rebel.

The youth was one of a group of M-19 guerrillas captured earlier that month. Several had been involved in the 1980 takeover of the Dominican Embassy in Bogota and had been flown to Cuba when the siege ended.

On March 22 the young wounded rebel said at a press conference that he and about 100 others had received guerrilla training in Cuba. He gave no names or details and none of the other captured insurgents corroborated his testimony. But the next day Colombian President Julio Cesar Turbay Ayala announced that relations would be suspended because of the Castro government's "hostile conduct."

Havana said it had not provided a single weapon to the M-19 and had nothing to do with their landing in Colombia. The question of training was not addressed.

Both Colombian and U.S. officials in Bogota reject any suggestion that Washington pushed for the break in relations.

But former foreign minister Alfredo Vasquez Carrizosa, now an outspoken critic of the Turbay Ayala government, said, "Undoubtedly the government has wanted for a long time to break relations with Cuba. I think the influence of the current United States policy determined the break. . . . There is no doubt that the United States is pressuring all the countries of the Caribbean to break with Castro. This is one example."

There is also no doubt that as the new cold war intensifies, Colombia is casting its lot with the United States, and the United States is openly showing its pleasure.

In addition to breaking with Cuba, Colombia has agreed to send troops to the U.S.-sponsored Sinai peacekeeping force. Colombia is fostering a development program for the Caribbean Basin that fits nicely with Reagan administration plans, reportedly has extended $10 million in bank loans and export credits to the anti-Castro government of Edward Seaga in Jamaica and signed an agreement with the Chilean military dictatorship to combat "Cuban expansionism."

Washington, meanwhile, has ratified a treaty with Colombia withdrawing the U.S. claim to some small islands also claimed by Colombia and Nicaragua. And the Reagan administration has made Colombia, after El Salvador, the biggest recipient of U.S. military aid in Latin America. Just last week the State Department announced the proposed $10 million sale of 12 U-1H helicopters to Bogota for use against its guerrillas.

"Maybe Turbay is an estimable person, even good," Castro said in a recently published interview. "But for me it's difficult to think he has these qualities when he allows himself to turn into a toy of the Colombian oligarchy, the Colombian Army and imperialism."

Castro also expresses a reserved bitterness about Costa Rica and its president Rodrigo Carazo.

Costa Rica's four years of diplomatic relations with Cuba never went beyond the consular level. They were plagued by reports of corruption in the Costa Rican consulate here and hampered by suspicions that Cuba's San Jose consulate coordinated much of the communist arms traffic in Central America.

But when Carazo gave a home to Castro's comrade-turned-antagonist Huber Matos after his release from Cuban prison in 1979, then accepted the first refugees in the 1980 exodus, relations worsened.

The official reason for Costa Rica's break with Cuba was Havana's response to a petition Matos submitted to the United Nations through Costa Rica denouncing Castro's treatment of political prisoners. Havana, in reply, reportedly accused Costa Rica of "servile support for counterrevolutionary maneuvers" and "unabashed" submission to the United States.

Tensions between Cuba and the Venezuelan government of president Luis Herrera Campins, have been worsening for some time.

Describing the problem of asylum seekers at the Venezuelan Embassy, Cuban Vice President Rodgriguez said: "On four separate occasions -- and I mention this as a sign of our patience -- previous Venezuelan governments . . . have asked us as a gesture of friendship to let people out that we had in there, and on four separate occasions we let four separate groups go out to Venezuela without their having any right, saying, 'okay, is this the last time?' 'Yes, this is the last time.' But it's not the last time. They come back again. They are people who enter with violence, people who enter with trucks they've armored themselves, who break down doors. You'll understand this won't do; that this game has to end."

Compounding the problem, President Herrera declined last year to move to change a decision by a military court to acquit four men accused of bombing a Cuban airliner in October 1976. All 73 aboard were killed in the crash.

Cuba was furious in the face of Herrera Campins' protestations that he could not interfere with the courts. Cuba closed its embassy in Caracas, and Venezuela recalled its ambassador from Havana.

Such refugees are also a central source of Cuba's problems with Peru and Ecuador.

Some diplomats here believe Peru, which used to have cordial relations with Cuba, was an unnecessary casualty of a larger ploy by Castro. By early 1980 the level of discontent in Cuba had risen dramatically and large numbers of Cubans, who would later join the Mariel exodus, wanted out. Castro warned both publicly and privately that something would have to give. Embassies, particularly of Latin countries, were being broken into constantly by Cubans seeking asylum.

After a Cuban guard was killed by people crashing a bus through the Peruvian Embassy gates Castro withdrew that embassy's protection on April 4, 1980. Within days 10,000 Cubans had crammed inside.

With the Peruvian Embassy, then Mariel, Castro apparently saw a way to relieve the pressure of domestic dissent.

The embassy invasions did not cease with Mariel and they remain, along with some of the original asylum-seekers, a festering problem here. Ecuador was angered when Cuban police entered the embassy and dragged out a group of unarmed asylum-seekers, in effect violating an accord negotiated by Ecuadoran diplomats.