By SAM DILLON

A prominent Cuban exile who escaped last year from a Venezuelan prison underwent plastic surgery, adopted a new identity, and uses the same name a captive American flier used to identify the shadowy figure who ran a clandestine operation to supply contra rebels, his friends and acquaintances say.

The exile, Luis Posada Carriles, told a Venezuelan journalist in a May interview in El Salvador that he had begun "a war without quarter" against communism in Central America. He said he underwent extensive plastic surgery in his attempt to adopt a new identity.

In Miami, meanwhile, one of Posada's close friends said Posada has used the pseudonym "namon Medina" since his escape, according to a reliable source.

Another friend of Posada said he thinks Posada and the "Ramon Medina" who allegedly helped run an Et Salvador-based contra supply operation are the same person.

"This is definitely the same guy," a reliable Cuban American source told The Miami Herald. "Posada's up to his neck in this stuff down there."

The emerging picture of the life of Posada since his mysterious August, 1985 escape from a high-security Venezuelan prison appears to support Nicaraguan claims that he is in fact the "Ramon Medina" fingered by captured American crewman Eugene Hasenfus. Hasenfus was formally charged Monday in Managua.

At the time of his escape, Posada was being held for the 1976 bombing of a Cuban jetliner that took 73 lives.

If true, Posada's participation in the rebel supply network suggests complicity by Salvadoran, U.S. or contra officials in helping an accused terrorist and international fugitive evade Venezuelan authorities.

Posada's wife, Nieves, said in a phone interview this week that she did not believe her husband was the man identified as Ramon Medina. Leonardo Somarriba, spokesman for the contra rebel organization UNO, said he had never heard of either Ramon Medina or of Luis Posada.

Posada, 58, is a fervent antiCommunist, Bay of Pigs veteran, self-described CIA agent, architect of Venezuela's late-1960s counterinsurgency campaign against Cubanbacked guerrillas, and a hero to many Cuban exiles.

Jailed in Caracas

He was indicted and jailed in Caracas along with three others, including Orlando Bosch, for the October 1976 bombing that destroyed a Cubana Airlines DC-8 minutes after it took off from Barbados for Havana. The crash killed 73, including several North Korean diplomats and the Cuban national fencing team.

Despite nine years of imprisonment and trial on the charges, Posada was never convicted and continues to protest his innocence. He escaped from Venezuela's San Juan de los Morros prison last year and disappeared.

Posada's name emerged last week after Sandinista officials said that Hasenfus, the U.S. captive, had identified Posada from photographs as the man he had known as Ramon Medina, working at San Salvador's Ilopango air base. Hasenfus said he believed "Medina" and his boss, another Bay of Pigs veteran known as Max Gomez, were both CIA agents.

Hasenfus' allegations were given strong support when a close friend of Posada disclosed to a reliable source in Miami that Posada has been working in E1 Salvador and using the pseudonym Ramon Medina. The source said Posada's friend has a Central American telephone listing for Posada in his address book under the name of "Ramon Medina Luis]."

The Sandinistas' allegations that Posada is working in the contra supply effort at Ilopango Air Base

have focused attention on a little-publicized interview with Posada by Venezuelan journalist Rafael Del Naranco, published May 12 in the Caracas-based daily El Mundo.

Naranco's article, which focused on Posada's escape and new involvement in the anti-Communist struggle in Central America, placed the interview in Central America.

El Salvador interview

Contacted Monday in Caracas, Del Naranco said he had interviewed Posada in El Salvador.

Del Naranco said that to get his interview with Posada, he flew from Caracas to Miami to Merida in southeastern Mexico, where he was picked up by a small propeller-driven plane that flew him "across two Central American countries" to a dirt airstrip in El Salvador where he spent the night.

Later he was. blindfolded and driven to another rural location where he met Posada, Del Naranco said.

Del Naranco reported that at the same time and place, a camera crew led by Miami resident Ernesto Avino filmed a three-hour interview with Posada.

Parts of Avino's footage of his interview with Posada were broadcast on Hollywood's Channel 51 two months ago as part of an hour-long Spanish-language documentary called El Caso del Avion Cubano - "The Case of the Cuban Plane."

In the interview, Posada appeared in crisp new camouflaged fatigues wearing a false white beard, and dark glasses. Seated on a hillside, Posada held an automatic rifle in his lap throughout the interview. A revolver was strapped under his arm.

Posada told his interviewers he had begun "a fight to the death and without quarter with Fidel Castro's agents." Del Naranco said that in his interview, Posada never mentioned involvement with the CIA. Nor did he describe the nature of his work.

Posada told Del Naranco that he had "extensive and complicated"

plastic surgery since his escape. Nonetheless, Posada's wife Nieves, who lives in Miami, said that when she saw her husband on television she had no trouble identifying him despite his beard and glasses.

"I knew him immediately by his hands and by his voice," Mrs. Posada said. "There's no doubt it was him."

Beard and glasses

She said that because of the beard and glasses she had been unable to determine if her husband had undergone plastic surgery.

She said she believed her husband had permitted himself to be filmed by friendly interviewers in order to articulate his protests against the Venezuelan justice system that kept him incarcerated without conviction for nine years.

Speaking to The Miami Herald, Del Naranco quoted Posada as saying that he had spent the first month after his escape last year hidden in the home of a former officer of Venezuela's secret police agency, DISIP.

Posada told Del Naranco he later had been taken by small plane to "a nearby island," by boat to another, and finally by plane to Central America, the journalist said.

In Del Naranco's published interview, Posada said he had received no help from Venezuelan police during his escape, but that "they didn't do much to find me."

Venezuela's justice minister told reporters last year that Posada's escape had involved the bribing of a prison guard supervisor. Venezuelan press accounts put the payoff at more than $25,000, a sum financed, according to unconfirmed Venezuelan reports, by an anti-Castro group.

In San Salvador, the man known as "Medina" lived in a two-story stucco house in the fashionable neighborhood of Escalon a 20-minute drive from Ilopango. His landlord told reporters that Medina had rented the house six months ago through a newspaper ad and had lived alone.

"lie paid cash every month, one month in advance," the landlord told reporters. "Medina said he was in construction. I figured he worked in the U.S. Embassy. He paid cash, that is all I wanted to know."

After Posada's escape last year, Miami backers organized a showing of his oil paintings in Coral Gables. A biography distributed at the showing said Posada was born Feb. 15, 1928 in Cienfuegos, Cuba and studied industrial chemistry at the University of Havana.

Posada began in 1960 to "struggle internally in Cuba against Castro's Communism, and he entered the CIA at that time," the biography says. After emigrating to Miami, Posada received training at a "clandestine CIA base in the Florida Keys," in map-reading, navigation, aerial photo interpretation, light arms management, and the use of explosives, the biography says.

70 infiltrations

Posada made more than 70 clandestine infiltration trips to Cuba before the Bay of Pigs. After the invasion's defeat he was trained with the 2506 Brigade at U.S. Army Forts Benning and Fort Jackson, the biography says. His work with the CIA also continued, with military participation in the Congo and in Vietnam, the biography says.

He remained a "principal agent" of the CIA until 1967, the biography says. That year he traveled to Venezuela, where his intelligence skills and political connections allowed him to rise to the powerful post of chief of operations of the DISIP, the Venezuelan intelligence service.

His biography credits him with "totally annihilating" several Cuban-trained guerrilla bands that infiltrated into Venezuela in the late 1960s. Posada left the Venezuelan police in 1974 with the reorganization of government that followed the election that year of Carlos Andres Perez, and founded a private security firm.

It was at these private offices that Venezuelan police arrested him in October 1976, accusing him of conspiring with Bosch to bomb the Cuban airliner.

Sandinista officials asserted last week that Hasenfus had told them he believed that both Max Gomez and "Ramon Medina" had the blessing of Vice-President Bush for their contra supply work at Ilopango air base.

Bush has denied knowing "Medina," whose whereabouts are unknown. So are Podosa's.