Michael V. Townley, the government's key witness in the Orlando Letelier bombing assassination trial, has told the FBI that in one of numerous personal calls he has been allowed to make to Chile from prosecutors' offices he may have suggested that friends should threaten the judge in the case.

Townley, an American-born Chilean secret police agent who has confessed to planting in Letelier's car the bomb that killed the former Chilean ambassador, told U.S. District Judge Barrington D. Parker yesterday that he called another former Chilean secret police agent from the prosecutor's office Jan. 30 without permission.

The purported transcript of the Jan. 30 call became an issue on the day when the jury heard its final testimony in the case against three anti-Castro Cubans on trial in connection with the Letelier slaying. But the call also added a new chapter to the already-bizarre life of Townley, 26 a native of Waterloo, Iowa, who calls Chile his homeland and refers to that country's DINA secret police as "my service."

The call, according to sources familiar with it, was recorded in Chile by an ally of Juan Manuel Contreras Sepulveda, the former DINA chief awaiting a decision by the Chilean Supreme Court on whether he is to be extradited to stand trial for Letelier's murder.

But Judge Parker, under an agreement with Townley's atorney, stopped short of asking Townley whether he suggested in the telephone call to the former agent, Gustavo Etchepare, that friends should call the judge to threaten him in the hope that he would withdraw from the case.

Parker rejected a bid by defense lawyers for the three Cubans to have Townley testify about the telephone conversation in front of the jury. The defense lawyers felt that with the transcript they could discredit Townley, who in six days of testimony last month methodically recounted how he was ordered by his DINA, superiors to kill Letelier and how he carried out the mission.

Defense lawyers Paul Goldberger, Lawrence Dubin and Oscar Suarez gave Parker a copy of the purported transcript of the Jan. 30 call to Etchepare. But prosecutors Eugene M. Propper and E. Lawrence Barcella Jr. told Parker that the transcript might be partly fabricated and that the tape of the conversation might be a spliced collection of statements only partly those of Townley.

Sources close to the case said Townley confirmed to the FBI that he made general remarks about the trial and legal strategy in the case that are contained in the transcript given by the defense to Parker. But Townley said he was unsure whether he made the suggestion about threats against the judge, according to the sources.

Townley's lawyer, Seymour Glanzer, said he is convinced after talking to Townley that Townley did not make any threats against the judge or suggest that anyone else make the threats.

The purported tape was given to defense attorneys last week by Sergio Miranda Carrington, Chilean lawyer for Contreras.

Sources familiar with the tape said Etchepare's telephone was bugged and the tape made by still another former DINA agent, Jose Fernandez Schilling.

A source close to the prosecution said there has been a "real concerted effort by Contreras to discredit Townley and this apparently is part of it." Earlier this week, two former DINA agents came here offering to testify for the defense in an effort to discredit the government's star witness. But defense attorneys rejected the offer.

Townley told Parker that he had made at least one other personal call to Chile from the prosecutor's office since finishing his testimony. Townley has made repeated calls to Chile at the prosecution's behest, according to one source, in order to learn information the government needed for its case.

But the source said that Townley has been billed for strictly personal calls to Chile and that in at least one month the bill totaled between $200 and $300. In the federal courthouse here, Townley has been in custody of U.S. marshals, but he has had free access within the prosecutor's office and even yesterday after his testimony could be seen strolling there casually.

In the call to Etchepare, Townley allegedly said FBI agents also discussed possible threats against the judge. FBI agents involved in the case flatly denied discussing threats, but the FBI said there would be an investigation of the matter.

The jury heard testimony yesterday on Townley's contacts in the early 1970s with the Central Intelligence Agency. One CIA official, Marvin L. Smith, said Townley once was given "conditional operational approval" to work for the agency but was never used in such a capacity The defense has claimed that Townley was working for DINA and the CIA.

The jury is expected to hear final arguments Monday before considering a verdict.