By JUAN deONIS

MIAMI-Cuban exile extremists who have been accused of terrorist activities against the Government of Prime Minister Fidel Castro have been tolerated, if not encouraged, by several Latin American countries.

The crash of a Cuban airliner off Barbados on Oct. 6 in which all 73 people aboard were killed has drawn international attention to a campaign of harassment against the Communist leadership of Cuba that has been under way in the Caribbean area for months.

There have been bombings of Cuban diplomatic missions airline offices and press service bureaus in Panama, Colombia, Barbados and Trinidad and Tobago and an attempt to kidnap the Cuban consul in Merida, Mexico.

The extremists, believed by the police here to number no more than several hundred, are a small minority of the emigres who left Cuba after Mr. Castro seized power in 1959. Miami is the Drincipal center of Cuban exiles. with about 500,000 living here.

Six Indicted in Venezuela

In the case of the Cuban airliner, six persons, including Dr. Orlando Bosh, a Cuban exile physician, have been indicted in Venezuela on charges of sabotage. The others include Luis Posada Carriles, a Cuban-born naturalized Venezuelan citizen who was trained by the United States Central Intelligence Agency and who has been running a private detective agency in Venezuela.

Dr. Bosch, who has worked in Miami as a pediatrician, violated probation by leaving the United States after he was paroled in 1974 from a l0-year prison sentence for firing a rocket at a Polish ship anchored in Miami. He was nevertheless allowed to move freely from Venezuela to Chile, Nicaragua, Costa Rica, the Dominican Republic and back to Venezuela.

Several Miami residents and Dr. Bosch met in the Dominican Republic in July and issued a statement declaring their intention of waging a terrorist campaign against Cuba.

Cuban sources here said Manuel Artime, a former commander of American-trained anti-Castro raiders, had been in touch with Dr. Bosch and other exiles in Nicaragua, where President Anastasio Somoza is an ardent opponent of the Castro Government and a business partner of Mr. Artime.

Offered to Return Bosch

on two occasions, when Dr. Bosch was arrested in Venezuela and Costa Rica and offers were made to send him back to the United States as a parole violator, the Department of Justice refused to have him returned. Now that he has been implicated in the Cuban airliner case, the United States Embassy in Venezuela has asked that he be returned if not convicted.

According to the Miami police, Cuban exile extremists operate in a murky underworld, where anti-Communist and patriotic motives are often mixed with criminal extortion to obtain funds and with traffic in arms and drugs.

Their activities have also affected relations between Cuba and other Caribbean countries as well as future United States!, Cuban relations under a new administration in Washington.

The recent increase in anti-Castro activities followed a decision by the Organization of American States in March 1975 to end the break in diplomatic and economic relations with Cuba. Nine member countries have now restored relations. Any such normalization is opposed by the anti-Castro militants and by rightwing governments, like those of Chile and Nicaragua.

U.S. Policy Has Shifted

The United States, in a shift of policy reflecting detente, appeared to be encouraging normalization until Cuba sent forces to Angola in late 1975 to support one of the rival factions there.

The renewed activities of the Cuban exiles raise questions over their base of support, the source of their funds, and the nature of their political relations.

Exile sources here say the extremists' activities are financed by wealthy Cubans in Miami and in other Caribbean centers. Some might doctors are making as much as $100,000 a year and, according to a Cuban who knows Dr. Bosch, have been giving him money so as to feel part of the anti-Castro movement.

It is also clear that the militants maintain good relations with the governments of Nicaragua and the Dominican Republic, where planning meetings have taken place. 1n other countries, such as Venezuela and Costa Rica, Cuban exiles with influence have provided protection for the militants.

Many Had CIA Training

The movements of Dr. Bosch also raise questions about the United States Government's attitude toward the militants, many of whom were trained by the C.I.A. for the abortive Bay of Pigs invasion in 1961 and later mounted other raids into Cuba. Since 1973, an antihijacking agreement between the United States and Cuba was considered to have put a halt to American support for the exiles.

Venezuela offered to send Dr. Bosch to the United States in November 1974 after he had been arrested on chargers of having planned an explosion at the Cuban Embassy there. The United States Embassy in Caracas said later that his case was not considered at a "political level" and that tile Immigration and Naturalization Service refused to allow his return on the ground that he was an undesirable alien. This account, however, is disputed by Venezuelan authorities.

Costa Rica offered to send him back last March after Dr. Bosch had been arrested on charges of participating an a bomb plot against Secretary of State Henry A. Kissinger during the Secretary's visit to that country.

Gonzalo Facio Segreda, who was Costa Rica's Foreign Minister at the time, said in an interview in Puerto Rico that the United States State Department was advised of the arrest of Dr. Bosch by the Costa Rican Ambassador in Washington, Rodalfo Silva.

"We offered to send him back," Mr. Facio Segreda said, "but the reply was speculation in Costa Rica that the United States refusal could have been politically motivated as it came just before the Presidential primary in Florida."

Dr. Bosch had arrived in Costa Rica from Chile, where he had been laving during most of 1975 alt a guest house of the strongly anti-Castro Chilean military Government. He came with a Chilean passport issued in the name of Hector D. Avanzo, and had been in Nicaragua, where violently anti-castro leaders openly support Cuban exile groups.

After the United States refused to take Dr. Bosch back, Mr. Facio Segreda said Costa Rica decided to expel him on his Chilean passport to the Dominican Republic, which granted him a visa.

But other Cuban exile sources in Costa Rican said he traveled with a Costa Rica passport, went to Nicaragua, and only arrived after in the Dominican Republic for a meeting of Cuban action groups in July. At this meeting, according to these sources, Dr. Bosch met with Frank Castro, a former United States Army officer of Cuban origin who, according to the Miami police, has a record of harboring Cuban extremists on the run from the United States; Roberto Carballo, representing the so-called 2506 Brigade that took part in the United States-sponsored Bay of Pigs invasion, and Felipe Rivero of the Cuban Nationaist Movement.

The meeting in the Dominican Republic declared a policy by the participating groups of attacking Cuban targets internationally, as well as within Cuba. It took a stand against terrorist actions within the United States, such as a series of bombings and assassinations in the Miami area that are now under investigation by a Federal grand jury and local police authorities.

Returned to Venezuela

On Sept. 18, according to Venezuelan immigration records, Dr. Bosch entered that country on his Costa Rican document, issued in the name of Paniagua. This document has not been found, but Costa Rica claims it is a forgery.

Dr. Bosch's arrival in Venezuela came three days before a bomb explosion in Washington killed Orlando Letelier, a former Foreign Minister of Chile and Ambassador to the United States for the left-wing Government of the late President Salvador Allende Gossens.

The Federal Bureau of Investigation has directed its effort to solve the killing of Mr. Letelier toward Cuban extremists, in part because of the close ties that have grown up between the Chilean military Government and Cuban exile groups that share anti-Castro militancy.

High Venezuelan officials admit that they knew that Dr. Bosch had entered the country despite his false identification, when, shortly after his arrival, he contacted Cuban exiles here.

Militant Policy Was Proposed

Cuban exiles described a meeting that took place in late September of the Jose Marti Patriotic Association, the principal forum here for the 50,000 Cuban exiles in Venezuela, where Dr. Bosch set forth his militant line of attacking Cuban targets abroad.

According to one Cuban in Caracas, the proposal split the association, with a right-wing splinter group led by a Cuban physician, Dr. Emilio Tebelio, proposing a toast to President Augusto Pinochet of Chile and pledging financial support for Dr. Bosch. The majority of the Cubans supported the position of the president of the association, Dr. Mario Rodriguez Perez, a lawyer, that Venezuela should not be used for operations against the Castro Government.

Orlando Garcia, who has been a close friend of President Carlos Andres Perez of Venezuela for 25 years and who serves as an adviser on security affairs, was in touch with Dr. Bosch in the days before the airliner crash, according to Cuban exile sources. But Government sources said he did not learn of the sabotage plan.

The Government sources said Dr. Bosch established contact with another Cuban intelligence expert who had lived in Venezuela since 1966--Mr. Posada, the detective agency operator, known as Bambi among Cuban exiles.

Mr. Posada, who is now under indictment, is not a friend of President Perez or the rest of the leadership of the ruling Democratic Action Party. He is close to the opposition Christian Democrats, who were voted out of office in 1974. In their former Government Mr. Posada was chief of operations of the national secret police.

Resigning from that job with the advent of the new administration, Mr. Posada opened his detective agency, which is known to have done such work as combating shoplifting at a major supermarket chain in Caracas.

The main suspect in the Cuban airliner case worked in Mr. Posada's agency and had been seen with Dr. Bosch, apparently serving as a bodyguard, before the crash. The suspect, Hernan Ricardo Lozano, reportdly boarded the plane in Trinidad and left it at Barbados. The airliner crashed a few moments after taking off from Barbados for flights to Jamaica. and Havana.

Police Raided Posada's Office

The Venezuelan police raided the office of Mr. Posada the next day and found a hand-written document, prepared in the style of an intelligence report, describing security conditions at Cuban diplomatic missions, airline offices and for planes traveling in the Caribbean to Havana from Panama, Colombia, Trinidad and Barbados. The flight on which the explosion occurred was also described.

Many well informed Cuban exiles interviewed in the Caribbean area do not believe that Dr. Bosch is a skilled extremist or sufficiently attractive ass a political figure to be able to obtain even covert support from anti-Castro governments.

He does not have a record as an active opponent of the former Cuban Government of Gen. Fulgencio Batista or as an early foe of the Castro leadership. But he is respected for having given up what could be an easy life in Miami, and he has a certain public esteem as a man of action, although he has no political program other than fighting for the downfall of Prime Minister Castro.

"The only thing that counts with the Cuban exile community is action," said a Cuban in Caracas who fought with Mr. Castro's 26th of July Movement against General Batista, then broke over the Communism issue and later took part in raids organized by .the C.I.A. "There is such frustration and lack of confidence in any of the old political figures that someone like Dr. Bosch can get support."

Bosch Is Still on Wanted List

WASHINGTON, Nov. 14 - A Justice Department spokesman has said that Dr. Orlando Bosch is still wanted by the United States Parole Commission for violation of parole two years ago.

The spokesman said recently that there was nothing in the parole files of the commission to indicate that Dr. Bosch was not on its wanted list.

However, it was learned that the Justice Department's Criminal Division apparently advised the State Department that it had no interest in the return of Dr. Bosch from Venezuela in 1974 and again had no interest in having him deported either from Costa Rica last spring or the Dominican Republic last summer.

The rationale presented to the State Department was said to be that since Dr. Bosch could not be legally extradited on a parole violation and was not otherwise facing criminal charges in this country, it vas preferable to leave him where he was.