By TIM GOLDEN

MANAGUA, Nicaragua - Sandinista security officials said Wednesday that a Cuban exile who allegedly helped run an El Salvador-based contra supply operation is an escapee from a Venezuelan jail where he was being held for the 1976 bombing of a Cuban jetliner.

Deputy Interior Minister Luis Carrion said Sandinista officials are convinced that Ramon Medina, identified by a captured U.S. pilot as the No. 2 figure in the contra supply operation, is in fact Luis Posada Carriles, one of four suspects - including Orlando Bosch - charged in the Cubana airliner bombing that claimed 73 lives. Posada Carriles escaped from prison last year.

Carrion said at a news conference Wednesday in Managua that Eugene Hasenfus, the American pilot captured two weeks ago, had identified Posada from photographs shown him by interrogators. He also cited other unidentified Sandinista intelligence sources he said indicated that Medina and Posada were the same person.

"We are certain that it's him," Carrion said.

Al Laun, U.S. Embassy spokesman in Managua, said the embassy had no official comment on the accusation.

"They can say he's been well-treated and that he's saying all this stuff voluntarily, but we really don't know;" Laun added. "We're certainly not taking their word for it.

Posada's wife Nieves, who lives in Miami, said Wednesday that the allegations were false.

"Say it isn't true," she said. "It is obvious that he [Hasenfus] is being forced to say these things."

Nieves Posada said her husband last telephone her on Monday, but that she doesn't know where he is or what he's doing. "Since he is in a delicate situation, I don't ask him those things," she said, "It could be true that he is in Nicaragua fighting with the guerrillas but I don't want to say."

Posada Carriles was arrested in Venezuela a few weeks after a bomb exploded in a Cubana Airlines DC-8 shortly otter it took off from Barbados on Oct. 6, 1976, heading for Havana.

A naturalized Venezuelan, Posada Carriles had worked for Venezuelan military intelligence. Venezuelan authorities accused Posada and Bosch as the "intellectual authors" of the bombing. Bosch, a Cuban exile pediatrician who formerly lived in Miami, became a folk hero to many in Miami's Cuban community during his long imprisonment in Venezuela while awaiting trial.

Posada Carriles escaped Aug. 18, 1985, from a national penitentiary in San Juan de los Morros, 60 miles southwest of Caracas. Venezuela's justice minister told reporters after the escape that Posada had bribed a prison guard supervisor.

Venezuelan press accounts put the payoff as high as $25,000, a sum financed, according to unconfirmed Venezuelan reports, by an anti-Castro group.

Posada paints in oils, and last November, his Cuban-American supporters organized a Coral Gables showing of his oil renderings of Venezuelan landscapes. The show, attended by Posada's wife but not by the fugitive, was a benefit for a Cuban couple accused by Venezuelan authorities of aiding his escape.

Posada's presence in Central America had been announced over Miami radio stations late last year. Tomas Regalado, general news editor at WQBA radio station said Posada's associates distributed a taped message from Posada to WQBA and other Spanish-language stations in which he said he had escaped from jail because he expected no justice in Venezuela.

Posada also said he was "fighting Communism in Central America."

Lenin Cerna, chief of Sandinista state security, said that Hasenfus, the captive U.S. pilot, had picked out Luis Posada's photograph from several others when asked to point out the man he had known in El Salvador as Ramon Medina.

Carrion, who directs Sandinista counterintelligence, said that Hasenfus described Medina as speaking perfect English and as a CIA operative who was a veteran of the 1961 CIA-directed Bay of Pigs invasion.

Posada, Carrion said, was identified by fellow Cubana bomber Hernan Ricardo as a recruiter for the invasion who was trained by the CIA in Florida and lacer participated in more than 70 operations for the agency from the Congo to Vietnam.

Posada's international exploits had been widely known in Miami. "Everyone knew he was one of those tough guys," said a source familiar with Cuban exile politics.

The source said that photos circulated in Miami of Posada in combat fatigues. The photos were said to have been shot in El Salvador the source said.

Venezuelan Foreign Ministry, press spokesman Tyson Medina, asked in a phone interview Wednesday about the Nicaraguan allegations, said the ministry "can't say anything. We don't know anything. We don't have any information:"

Carrion said that Sandinista officials had learned after Posada's escape that he had relocated in El Salvador and was using the name Ramon Medina.

Hasenfus told his interrogators that in the operation set up to supply troops of the Honduras-based Nicaraguan Democratic Force (FDN), the largest contra army, Medina-Posada arranged for U.S. Embassy documentation for pilots and crewmen, Carrion said.

He also coordinated flights out of the Salvadoran Air Force's Ilopango Air Base outside of San Salvador, Carrion quoted the U.S. pilot as saying.

Hasenfus, held in Managua's El Chipote prison, has been under interrogation by Sandinista officials since his capture Oct. 6. Cerna and Carrion said he was being treated well in detention and had cooperated freely with Sandinista intelligence officials.

"He said that he would be willing to cooperate because this wasn't his war," Carrion said. "He doesn't feel any obligation to conceal or retain any information he knows about the [supply] operation:"

Embassy spokesman Laun said that a U.S. consular officer had been allowed to see Hasenfus for only 11 minutes last week and that during that meeting Hasenfus was surrounded by Sandinista officials. Laun described the atmosphere as "very intimidating."

Hasenfus' wife Sally left Managua Wednesday and said through a U.S. Embassy spokesman that she was planning to see her children at home in Marinette, Wis., consult with lawyers and would then break her silence to the press.

Carrion said Sandinista officials would announce today when Hasenfus would be tried and by what courts. A government source said that Hasenfus would be tried in the Sandinista People's Tribunals, a court system set up under 1982 emergency laws that has been criticized by international human rights organizations. The U.S. Embassy protested this week against the possibility that the tribunals would hear the Hasenfus case.

In another development Wednesday, Carrion said a Cuban-American whom Hasenfus,

Salvadoran military officers and other U.S. sources have named as the head of the El Salvador supply effort "may" be a former CIA liaison to the rebels who went by the name Gustavo Villoldo.

The supply chief, a longtime CIA agent whose real name is believed to be Felix Ismael Rodriguez, had been previously identified by at least one other name. Hasenfus and Salvadoran military officers said he was known as Max Gomez.

Carrion and Cerna said Gomez, another Bay of Pigs veteran who U.S. officials have confirmed has worked for the CIA for many years, appears to fit the description of Villoldo, a Cuban-American who worked for the CIA In Honduras in 1983 and early 1989 as its liaison to the FDN general staff.

But they provided little clear evidence for their claim that Gomez, Rodriguez and Villoldo were all the same person.