A new legal wrangle has emerged in the Orlando Letelier assassination trial over a tape of a telephone conversation in which the government's key witness, former Chilean secret police agent Michael V. Townley, is alleged to have suggested that his friends threaten the judge in the case to get him to withdraw.

For three days now, defense lawyers for three Cubans charged in connection with the 1976 slaying have tried -- in secret bench conferences with U.S. District Court Judge Barrington D. Parker -- to persuade the judge to allow the jury to hear a transcript of the conversation.

But Parker has said nothing publicly about the alleged conversation last week between Townley and a friend of his from Townley's days in Chile, electronics expert Gustavo Etchepare.

There was no immediate way to determine that Townely, who has confessed to plainting the bomb in Letelier's car that later was detonated by remote control, actually participated in the Jan. 30 conversation. It allegedly took place, while he was in offices of the prosecutors in the case. The prosecutors have been given a transcript of the conversation, but have not listened to the tape of the dialogue, which was in Spanish.

Parker has sealed bench conference discussions about the tape and the tape transcript. Several times, however, he has alluded to it in ways that the defense and prosecution lawyers have understood what he was talking about.

At one point yesterday, Parker ordered that Townley be brought to the vicinity of the courtroom so that he could testify. But then the judge abruptly adjourned the trial for the day. He indicated in a bench conference that he might question Townley today about the telephone conversation, but that the questioning would take place either in a robing room behind the courtroom out of hearing of the public and the jurors or in the courtroom without the jury present.

The tape recording was given to defense attorneys Paul Goldberger, Lawrence Dubin and Oscar Suarez last week by Sergio Miranda Carrington, the Chilean lawyer for Juan Manuel Contreras Sepulveda, the former chief of the Chilean secret police once known as DINA. Contreras is awaiting a ruling by the Chilean Supreme Court on whether he is to be extradited to stand trial for Letelier's murder.

Defense lawyers for the three Cuban defendants have refused an offer by Miranda to have two former DINA agents testify as defense witnesses. The agents apparently were ready to try to discredit Townley.

According to a transcript of Townley's alleged telephone call to Etchepare obtained by The Washington Post, Townley told his friend: "If the good Judge Parker wants to listen, I'll do this, I offer at this moment to ask friends all over the world that they call him and threaten him so that he will withdraw from the case.

"This was one of things that was discussed among friends, with people of the FBI: How many friends would we have to make calls to the judge so he would withdraw from the case?"

Parker received two death threats before the trial started. But he rejected a bid from defense attorneys to withdraw from the case on grounds that the threats might have made him less sympathetic to the defendants. The prosecutors took no position on whether Parker should withdraw.

Townley, a native of Waterloo, Iowa, who now calls Chile his homeland, has referred to DINA during the trial as "my service."

During six days of testimony last month, Townley, 36, calmly recited the intricate details of how his DINA superiors ordered him to kill Letelier, a former official in the Marxist government of the late Salvador Allende, who was an outspoken critic of current Chilean military dictator Augusto Pinochet.

To varying degrees, Townley implicated all three Cubans on trial, Guillermo Novo Sampol, his brother, Ignacio Novo Sampol, and Alvin Ross Diaz.

Townley matter-of-factly recollected the assassination mission and at one point said he had no regrets about Letelier's slaying."He was a soldier, I was a soldier," Townley said.

His basic story was virtually unshaken after a rigorous cross-examination by defense lawyers. He did admit, however, that as part of a DINA cover-up of the Chilean involvement in the Letelier killing, he lied repeatedly to a Chilean investigator probing the case before the Chilean government turned him over to the FBI to testify in the current case.

Townley, who has spent 20 years in Chile, told the seven-woman, five-man jury that he became active in underground terrorist activities against the Allende government, later worked as an informant for DINA and then as an agent.

He testified that not all of his missions were as successful as the one to kill Letelier. In 1975, he said, he and his wife, Mariana, another DINA agent, arrived in Mexico a day late after being ordered to "eliminate" two other Chilean exiles. Townley is also alleged to have participated in attacks on Chilean exiles in Argentina and Italy.