The Sandinista government of Nicaragua has covered up thousands of cases of human rights violations and murder while financing its intelligence and espionage network through drug trafficking, a defector charged yesterday.

Alvaro Jose Baldizon Aviles, 26, who said he was the chief investigator of human rights allegations for Interior Minister Tomas Borge from late 1982 until July, told reporters at a briefing arranged by the State Department that he fled because "I came to realize how corrupt and bloody the Nicaraguan government was."

Baldizon, speaking through an interpreter, said one case he investigated involved the execution by firing squad of more than 150 Miskito Indians during the summer of 1982. But when Baldizon presented his 100-page report, which included sworn statements from soldiers and survivors, Borge "instructed that a second report be done up, giving a different and falsified version to cover up the responsibility of the Nicaraguan government in these human rights violations," Baldizon said.

He said he attended part of a meeting where officials from the ministry suggested that they could explain the disappearances by saying the Indians either went to fight for the armed resistance, known as contras, or else crossed the border to Honduras.

Baldizon said it was his idea to appear before the press.

"I am speaking voluntarily," he said. "I consider speaking out to be a right and a duty as a witness." In 1982, another Nicaraguan defector embarrassed the State Department by renouncing his hosts at a news conference and saying he had been coerced into talking.

Baldizon also said he had been told by a captain in Borge's office that Borge, one of the leaders of the Sandinista ruling body, personally removed bags of cocaine from a plane in the fall of 1984 and drove the drugs back to Managua. He said he was also told that the government made planes available and permitted the refueling of drug flights from Colombia to earn dollars to finance espionage. Baldizon acknowledged that he had no direct knowledge of such matters.

A Borge aide was indicted in Miami in July 1984 on cocaine smuggling charges.

The Nicaraguan Embassy issued a statement yesterday calling Baldizon's charges "one more desperate attempt by the administration to distract attention from the case brought by Nicaragua against the United States in the World Court. Sound policy must be based on facts and not on absurd and groundless accusations."

The United States has chosen not to appear at the World Court hearings in The Hague, where Nicaragua has charged the U.S. government with violations of international law by financing rebel operations.

John D. Blacken, deputy director of the State Department's Office of Public Diplomacy for Latin America, said Baldizon is considered one of the most valuable recent defectors from Nicaragua because of his work for Borge and his knowledge of the drug trafficking.

Blacken said that Luis Carrion, who was Borge's vice minister and heads the Nicaraguan delegation to the World Court, was implicated by Baldizon for signing what the defector called "special measures, a technical term to mean the physical elimination of human beings." Baldizon said "special measures" were performed in a "helter-skelter" manner after the Sandinistas first took power. But since 1981, such actions required approval by Borge or a top aide, Baldizon added.

He also alleged that prisoners in Nicaraguan jails are routinely kept naked in small cells before being questioned, still naked, in larger rooms with huge air conditioners blowing on them.

In a related matter yesterday, Assistant Secretary of State Elliott Abrams met with contra leaders at the department and said afterward that the first part of $27 million in humanitarian aid approved by Congress should be released to the resistance by the end of the month.