Cuban President Fidel Castro has been financing arms purchases by El Salvadoran guerrillas on the black market in the United States and elsewhere, according to a former Cuban official recently granted asylum here.

Jose Luis Llovio Menendez, once the chief adviser in Cuba's Finance Ministry, said Castro is too shrewd to risk direct shipments of arms or to send advisers into El Salvador.

"He has other ways to fight the Americans," Llovio said in an interview arranged partly to attract attention to memoirs he is trying to publish. "When he had to have gun machines for El Salvador, he gave money and they buy it on the black market here in the United States."

Llovio has been described by government officials as the most prominent defector from Cuba in recent years. Llovio said he and his wife fled the country in 1981 after he had spent more than a decade looking for a way out. He said Cuba has a sluggish economy, a reluctant work force, and a ruling "revolutionary bourgeoisie" corrupted by a constant scrambling for perquisites and power.

At the top, he said, Castro remains an "egocentric" leader, shrewd, charming and gripped by an abiding hatred for the United States.

But Llovio said Castro is too smart to enter combat with the United States in Nicaragua or elsewhere. "He cannot afford that," Llovio said.

Llovio said he left Cuba so quietly that he had difficulty convincing U.S. consular officials, first in Canada and later in Venezeula, that he was who he said he was.

Interviews with The Washington Post and others were arranged by Roger Young, a former assistant FBI director and spokesman, who said he had been asked to help out as "a friend of a friend."

Already interviewed numerous times by "U.S. officials," Llovio told of life as a reluctant Cuban bureaucrat, interrupted near the outset by a still-unexplained imprisonment, and finally concluded at the Montreal airport on Dec. 13, 1981, when he nervously asked a Canadian immigration official for asylum. His plane had stopped in Montreal for refueling during a flight from Czechoslovakia to Cuba.

Llovio said his disenchantment with the Castro revolution began early. He said he did not "defect" in the usual sense because "you have to believe in something to defect . . . .

"I believed in the revolution," he said. "It was not the one I saw. I believed in a better Cuba. It was not the one I saw . . . . I don't believe in socialism there. Because it does not exist."

He said he is "sure" that when he left in 1981, Cuba had been supplying El Salvadoran guerillas with money to buy U.S. and other western arms, using the Interior Ministry's "exterior expenses" budget.

"He [Castro] gave money, he is giving money, and he will give money [to the guerrillas]," Llovio said. "But he will do it in a [secret] way -- because he knows very well that if there is somebody that is going to catch one Cuban adviser in El Salvador . . . or catch some Cuban gun machine in El Salvador, he will have a lot of problems."

Llovio said, however, that the Cubans still were anxious to avoid any direct arms shipments to El Salvador. He agreed that "Cuba sends a lot of guns to Nicaragua," but said what Nicaragua does with them "is a Nicaraguan problem, not a Cuban problem."

Born in Camaguey of a middle-class family, Llovio signed up as a revolutionary in the early 1950s when he became a medical student at the University of Havana, "smuggling guns . . . engaging in a lot of manifestations, doing the normal thing."

He said he met Castro in 1955, but thought him "a very strange person . . . a little bit egocentric." Llovio stayed away from Castro's 26th of July Movement for some time but eventually joined it.

By early 1958, Llovio said, he had had enough. "Everything was 'Fidel says this, Fidel says that,' " he said.

Llovio went to France to study medicine at the Sorbonnne and rejoined the revolution from afar, helping to raise funds and stick a 26th of July flag in the Eiffel Tower.

Not long after his return to Cuba, Llovio said he received a visit from State Security police, assigning him "a little job." He was to "infiltrate all the elite" in positions of power and "inform them [the police] every 24 hours . . . . I did not have a choice."

Llovio said he was shocked. "The corruption was very big -- living high, drinking, women, not working, taking all of the things from the state for personal purposes."

Meanwhile, Llovio was given a job in the Ministry of Construction although he knew nothing about it. In Cuba, he said, "you have a Minister of Education who was a basketball player. In a revolution, you have to go where they want you to go."

In March 1966, he was eating a pizza when someone from the Interior Ministry stuck "a pistol in my back" and sent him to a windowless cell in an old seminary with some of those he had informed against. He said he now suspects that it was to keep his role a secret, but he still isn't sure.

Before long, he was assigned as a medical officer to a camp in Camaguey, part of a brutal, punitive system for misfits such as homosexuals and Jehovah's Witnesses. Llovio said he protested the conditions to the Army, which promptly assigned him to help "get rid of the camp in six months."

Mission accomplished, he was sent back to Havana where he worked five years for the Cinema Institute, first "as a laborer," then as "investment director." He did so well, he said, that in 1972, he was named "investment director of the whole sugar industry," another field about which he knew nothing.

Llovio said he muddled through, primarily by going to work as a sugar mill laborer before taking on bigger chores. Along the way, he met his present wife, Maggie Hollands, a graphic design student who later became art director of Cuba's monthly Revolution and Culture.

Llovio said he was tapped by Finance Minister Francisco Garcia Valls in early 1977 to be "his chief of advisers," aided by 12 officials from the Soviet Union.

"They the Soviets handle all the budget, all the money," he said.

A new assignment came up in the spring of 1979: inspecting Cuban embassies in Western Europe. "I discovered a lot of things that was not good . . . a very big corruption," Llovio said. He told the finance minister, who told Castro, but he only received more such thankless assignments, to Panama and then to the Fisheries Ministry, "the most corrupt in Cuba."

Llovio apparently stepped on too many toes. He told the finance minister of his findings about the Fisheries Ministry, and was told "you are fired," ostensibly because of his imprisonment 13 years earlier.

Devastated, especially since he had been planning to use his official position to take a vacation and flee, Llovio wrote Raul Castro and was soon restored to respectability, this time as an adviser in the Ministry of Culture. He worked there until 1981 when he and his wife took the plane to Czechoslovakia.

During all those years, Llovio said, he kept his own counsel, to the point that he found himself walking along the beachfront, talking to himself to relieve the tension. He first told his wife of his escape plans while they were swimming, hundreds of feet from shore.

It took Llovio more than a year to get to the United States after his arrival in Canada. Although he had been "a very high-ranking official" in Cuba, he said he ran into a blank wall on a visit to the U.S Consulate.

Frustrated, Llovio said he decided to visit his mother in Venezuela and finally received permission to enter the United States from there on Jan. 23, 1983. He was granted one-year asylum status in October but said he did not receive the papers "until a few days ago."