Defense lawyers launched their cross-examination attack yesterday on Michael Vernon Townley, the key prosecution witness against two anti-Castro Cubans accused of the 1976 assassination of Orlando Letelier, with a barrage of questions bearing on a tape-recorded telephone conversation in which Townley said he would recruit friends to threaten the trial judge in the case. t

Townley, clearly struggling to maintain his cold, matter-of-fact courtroom demeanor, said the remark was a "comment made in anger" to a friend who had "simply lit my fuse." Townley, 38, at times looking directly at the jury as he testified, said he make the remarks -- which he called "outlandish" -- to persuade his friend that the phone line was not tapped.

Townley made the telephone call to Gustavo Eschepare, a close friend in Santiago, Chile, while Townley was alone in a federal prosecutor's office in January 1979 at the end of the first trial of the two Cubans. Their convictions of conspiracy and murder charges in that trial subsequently were reversed by the U.S. Court of Appeals.

An American-born agent of the Chilean secret police, Townley pleaded guilty to conspiracy to murder a foreign official and is now in prison. Yesterday, Townley testified that he considers Chile his homeland and hopes eventually to return there. Asked by defense lawyer Paul Goldberger if he still considers himself a Chilean secret police agent, Townley replied with a smile, "No, sir," and added that "at least I haven't been paid any salary."

The government contends that Townley recruited the Cubans to kill Letelier under orders from secret police officials. Townley has admitted that he planted the bomb under Letelier's car, which was detonated by remote control at Sheridan Circle on Embassy Row, and has testified that the Cubans supplied explosives and participated in the murder plot. The defense says it will prove that it was Townley and the Chilean secret police alone who carried out the murder plot, and then tried to blame the Cubans.

The tape recording of Townley's conversation with Eechepare, the origin of which is unknown, was made available to the defense by an attorney for the former head of the Chilean secret police. At the first trial in U.S. District Court, Judge Barrington D. Parker refused to allow the defense to question Townley about his comments and the appeals court subsequently ruled that he was wrong about that. From the outset of the retrial, defense and prosecution lawyers have argued over the use of the tape, but Parker finally agreed that portions of a transcript of the tape could be used by the defense.

Yesterday, defense lawyer Goldberger opened his cross examination with a question about that telephone call and read a comment from Townley that asserted that "if his honor Judge Parker wants to listen . . . I offer myself at this time to ask friends in all parts of the world, let them call him and threaten him and let him withdraw from the case."

Townley, who vigorously denied that he ever threatened Parker or ever asked anyone else to do so, said the remark was taken out of context, that he was trying to prove to Eechepare that the line wasn't tapped and said they were "remarks I regret having made." Government prosecutors, in their objections to the tape, have contended that the text of Townley's conversation was altered.

The two defendants, Guillermo Novo Sampol and Alvin Ross Diaz, both Anti-Castro Cubans, were indicted with two other Cubans, now both fugitives, and three Chileans, including the head of the Chilean secret police, in connection with the car-bombing murder of Letelier and an associate, Ronni Karpen Moffitt. Chilean courts have refused to extradite the three Chileans to this country for prosecution.