By ALFONSO CHARDY

WASHINGTON - A Cuban exile wanted by Venezuela in the 1976 midair bombing of a Cuban airliner played a key logistical role in a controversial State Department program to provide humanitarian aid to the Nicaraguan contra rebels, according to a former State Department consultant.

But the consultant, Robert Owen, who also served as a messenger between Lt. Col. Oliver North and the contras, said that at the time neither he nor North knew that Luis Posada Carriles, a one-time CIA agent, Bay of Pigs invasion veteran and explosives expert, had escaped from a Venezuelan jail where he had been imprisoned in connection with the bombing. All 73 people aboard the Cubana DC-8 were killed.

Robert Duemling, the former director of the now-defunct State Department program, said that he did not know of Posada Carriles' involvement with the humanitarian aid project and that the Cuban was not on the program's payroll. The State Department declined comment.

Militant anti-Castro activist Orlando Bosch, who was accused of masterminding the bombing, was acquitted by a Venezuelan judge and ordered released Aug. 7 after spending nearly 11 years in a Venezuelan jail. The whereabouts of Posada Carriles, who escaped from prison in August 1985, have not been known since his presence in Central America was revealed last October.

Eugene Hasenfus, an American cargo handler who was captured last October after Sandinista soldiers shot down his plane, had identified Posada Carriles as one of two Cuban exiles who helped to organize a clandestine contra supply network overseen by North and headquartered at El Salvador's Ilopango airfield. The supply operation was financed in part by profits from arms sales to Iran.

But Posada Carriles' role in assisting the State Department's Nicaraguan Humanitarian Assistance Office (NHAO), which oversaw a congressionally mandated program to provide $27 million of humanitarian aid to the contras, has not been previously disclosed. The $27 million program has been the focus of allegations that some of the money might have been used illegally for weapons purchases.

How Posada Carriles came to be involved with efforts on behalf of the contras has been a mystery.

The matter was addressed only once by the congressional committees investigating the Irancontra scandal, when Felix Rodrigues, another Cuban exile involved in the supply operation, claimed responsibility for bringing Posada Carriles aboard.

"I helped him," Rodriguez, who also used the alias Max Gomez, testified. "I am the only [one] responsible for him to be there, nobody else and I don't regret what I did."

Rodriguez, who also worked at Ilopango, did not say, however, how Posada Carriles escaped from Venezuela. Rodriguez is a friend of Vice President George Bush and once was a CIA agent who helped the agency and the Bolivian government in the capture of CubanArgentine guerrilla leader Ernesto "Che" Guevara in 1967.

Owen, who was a paid consultant to NHAO until June 1986, told The Miami Herald in a series of recent interviews that Posada Carriles simultaneously assisted North's arms supply network and the humanitarian aid system.

Owen said that Psada Carriles1, who went by the code name of Ramon Medina, was responsible for receiving, refueling and relaunching the airplanes that both North's supply network and the NHAO humanitarian aid program dispatched from Ilopango. Duemling said that some NHAO planes were serviced at Ilopango, but that the majority landed in neighboring Honduras.

"At Ilopango, Ramon received the NHAO planes coming down from the United States with humanitarian cargoes and then had the planes refueled for the return trip," Owen said.

"One of the times I remember dealing with Ramon was in the spring or summer of last year

[ 1986 ] when I flew down aboard a C-46 aircraft loaded with NHAO stuff and Ramon turned up at Ilopango to receive the plane, then made sure that we got fuel for the return trip," Owen said. "That was his job."

In an Owen memo of March 28, 1986, to North released by the Iran-contra congressional committees, Owen said that he, Posada Carriles, Rodriguez, Rafael Quintero and the chief U.S. military adviser in El Salvador, Col. James Steele, had decided to merge the covert arms supply network and the overt humanitarian aid program to improve the efficiency of the contra-aid delivery system. The memo said it had been decided to stockpile both weapons supplies and humanitarian aid at Ilopango.

During North's testimony to the committees last month, the panels released a chart of the arms supply network that listed Posada Carriles- as "support-director" at Ilopango. The committees also released a description of the support director's job.

It said that the support director's responsibilities included keeping the project manager informed on personnel matters, housing, transportation, telephones, bills, expense reports and the arrangement with the Salvadoran air force for the refueling of contra supply aircraft.

It is understood that Lawrence Walsh, the Iran-contra special prosecutor, specifically is investigating the refueling arrangement because of the possibility that U.S.-financed airplane fuel might have been used to supply the contra arms delivery planes.