Threats against the lives of a prosecutor and the judge in the upcoming trial of three Cuban exiles charged in connection with the bombing death of former Chilean ambassador Oriando Letelier were made shortly after indictments were returned in the case last August, it was revealed yesterday.

Assistant U.S. Attorney Eugene M. Propper, who has investigated the Sept. 21, 1976, Embassy Row car explosion since the day it occurred, said that he received a telephone call in his federal courthouse office last Aug. 17 from a man speaking in English but with a Spanish accent.

The threats were revealed yesterday by Paul Goldberger, an attorney for one of the Cubans who are scheduled to go on trial Jan. 9 in Parker's count.

Goldberger and another defense attorney, Lawrence Dubin, suggested to Parker that the threats on his life might tend to make him less sympathetic to their clients.

But Parker said, "I have no problems with respect to an open mind" concerning the case. "I have no problems at all.

"I don't know of any judge who at some time hasn't incurred the wrath of some political group," Parker said.

The judge said that a day or two after he was randomly assigned to preside at the trial of three leaders of the Cuban Nationalist Movement-Ignacio Novo Sampol, Guillermo Novo Sampol and Alvin Ross Diaz-he received a couple of nuisance calls at home in which the caller slammed the receiver down as he answered. But he said the caller did not mention the Letelier case.

Propper declined to say exactly what the caller said to him. But he submitted an FBI report on the incident to Parker, who sealed it at Proper's request. The judge said he had D.C. police protection for a day or two after the call to Propper, while the prosecutor said later that he now has an unlisted home telephone number.

Parker denied most of the defense motions yesterday for large numbers of government documents that the defense lawyers said may be in some way related to the case against the Novo brothers and Ross. But the judge directed Propper and Assistan U.S. Attorney E. Lawrence Barcella Jr. to try to learn the identity of four federal Bureau of Alcohol, Tobacco and Rirearms agents who were seen in a cul-de-sac near Letelier's Bethesda home on the morning of the assassination.

After Goldberger said the Leteliers' housekeeper had seen the men, Barcella replied that the housekeeper may have seen the agents, who were in a gray sedan, but that she could not describe them. Barcella said the ATF agents were working on a "totally unrelated investigation there," but he said he did not know what it was.

Parker ordered the prosecutors to find out more about the ATF investigation and give him a report on it.

Parker denied defense attorneys' requests for about 70 pieces of information, including government reports on all Cuban exiles in the United States. But the prosecutors said that by Jan. 3 the government will have turned over to defense attorneys almost all the evidence it plans to use in the trial.

Barcella and Propper said, however, they hope the judge will allow them to keep secret the names of two or three prosecution witnesses until the night before they are scheduled to testify because of fears for their safety if the names are made public.

Parker also asked the prosecutors to provide him with a list of the contents of Letelier's briefcase found in the wreckage of his car.

But the judge denied a defense request that the government determine whether a Coral Gables, Fla., firm called Audio Intelligence Devices Inc. is a front for the Central Intelligence Agency. Goldberger said that the government's key witness in the case, Michael V. Townley, an American-born Chilean secret police agent, was seen at the company on the day of the assassination, and the day after. The firm, according to sources close to the case, supplies countries throughout the world with various eavesdropping paraphernalia.

Gullermo Novo and Ross are charged with conspiracy to murder Leteher and the murder of Letelier and an aide killed in the same blast, Ronni K. Moffitt. The Novo brothers also are charged with two counts of lying to a grand jury and Ignacio Novo is also charged with failing to tell law enforcement authorities about the crime after it occurred.