SAN SALVADOR, DEC. 16 -- In a videotape reportedly made by the CIA for distribution throughout Central America, a former top aide to Nicaraguan Defense Minister Humberto Ortega embraces the "heroic struggle" of the U.S.-backed Nicaraguan rebels and charges his former boss with corruption and sexual misconduct.

Former major Roger Miranda Bengoechea, in a highly personal 45-minute statement broadcast last night on the government television station here, attempts to explain why he left Nicaragua and denies Sandinista charges that he is a thief and a traitor. The videotape and an audio version also have circulated in Honduras and Nicaragua.

None of his charges against Humberto Ortega, brother of President Daniel Ortega, could be verified immediately, and Miranda offered only his word as someone who had been a close collaborator of the Ortegas since they were fighting to overthrow the government of Anastasio Somoza. The tape only shows Miranda speaking, and no questions are asked.

The videotape was clearly designed to paint Sandinista leaders as members of a privileged class who have betrayed the goals of the revolution, a favorite theme of the opposition in Nicaragua.

The tape is expected to be used to bolster the contention of Salvadoran President Jose Napoleon Duarte and the U.S. Embassy that the Nicaraguan government is arming and training Marxist-led guerrillas here, despite the ban on such aid under a regional peace plan. Miranda told reporters in Washington that the Nicaraguan Army has trained Salvadoran guerrillas in the use of surface-to-air missiles.

Sources at the television stations showing the tape in El Salvador said they thought it was provided by the contras, but would not give specific information. The CIA organized and advises the contras.

Informed sources in Washington said the CIA was involved in making and distributing the tape. A senior White House official said the content of the tape was approved by the National Security Council Staff. He added that the White House is "not ashamed" of the videotape and will make a transcript public.

A State Department spokesman said the tape is being made available to U.S. embassies in the region.

Sources said the tape could not be shown in the United States, because the CIA is barred by law from "propaganda activities within the United States."

The statement was couched as a greeting to Nicaragua and the contras. The signals of some Salvadoran television stations, including the government station, are received in parts of Nicaragua.

Miranda was the head of the Defense Ministry's administrative arm from 1982 until he defected Oct. 25.

Miranda said he became disillusioned with the growing "corruption and immorality" of the nine-man National Directorate of the Sandinista front, and finally decided to leave.

"Humberto Ortega and the rest of the Sandinista leadership are the biggest traitors and most immoral in the history of Nicaragua," Miranda said. "Humberto Ortega not only betrays the Nicaraguan people, but also betrays his most intimate friends and closest collaborators, enjoying their wives and taking advantage of his position."

Miranda said Ortega had maintained sexual relationships with the wives of at least three leading Sandinistas. While he did not mention specific charges against others in the directorate, he said he knew some behaved similarly.

Miranda offered no evidence for the accusations.

He said Ortega had a sexual relationship with the wife of a high-ranking officer in the Popular Sandinista Army until he decided that it was too dangerous. He said President Ortega took the officer with him on foreign trips, so his brother could see the man's wife.

Washington Post staff writers in Washington and Central America contributed to this report.