If things had gone his way, William M. Kunstler, the lawyer prominent for representing many political radicals, would have had a starring role as the chief defense lawyer in the biggest terrorism trial ever to come to an American courtroom. 
Instead, Mr. Kunstler appeared yesterday in a cameo role, barely an hour long, as a defense witness at the six-month-old trial, in which 11 Islamic men are charged with a terror-bombing and assassination conspiracy. 
But if the subject of Mr. Kunstler's testimony was peripheral at best in the case in Federal District Court in Manhattan, the 76-year-old warhorse of left-wing legal crusades showed that he could be as wily and entertaining as a witness as he usually is as a lawyer. 
He bantered here, slyly slipped in an improper but helpful-to-the-defense aside there -- performing like a combination of Perry Mason and Jackie Mason. 
"How are you?" one of the prosecutors, Andrew C. McCarthy, said as he approached the lectern to cross-examine Mr. Kunstler. 
"What are you, my doctor now?" Mr. Kunstler shot back, sparking some smiles in the jury box and chortles on the spectator benches. 
The defendants are charged with a conspiracy that prosecutors say included the 1993 bombing of the World Trade Center in Manhattan, in which six people were killed, and aborted plots to bomb such other major New York area sites as the United Nations headquarters and the Lincoln and Holland tunnels. The defendants say the case is trumped up. 
Back when the case was in its pretrial stages -- after the defendants were arrested in the summer of 1993 -- Mr. Kunstler seemed to be all over the defense side. He and his partner, Ronald L. Kuby, not only represented the chief defendant, Sheik Omar Abdel Rahman, but two others as well, Ibrahim A. Elgabrowny and Siddig Ibrahim Siddig Ali. 
But in late 1993, the judge, Michael B. Mukasey, said it would be a conflict of interest for the two lawyers to represent all three and told them to decide which client or clients they wanted to give up. When they refused, he chose for them, designating their clients as Mr. Elgabrowny and Mr. Siddig Ali. 
Then, 13 months ago, Mr. Siddig Ali dropped Mr. Kunstler and Mr. Kuby as he took his first steps toward pleading guilty to conspiracy charges. And last August, Judge Mukasey disqualified the two lawyers from representing Mr. Elgabrowny, saying their conflict of interest continued because of their previous representation of Mr. Abdel Rahman and Mr. Siddig Ali. 
And so, there was Mr. Kunstler yesterday, reduced to a quick-passing defense witness, called by Roger L. Stavis, a lawyer for another defendant, El Sayyid A. Nosair. Mr. Kunstler represented Mr. Nosair in a 1991 state trial in which Mr. Nosair was charged with the 1990 killing in Manhattan of Rabbi Meir Kahane, the Jewish militant. Mr. Nosair was acquitted of murder in that trial but convicted of gun possession and other lesser charges. 
Mr. Stavis called Mr. Kunstler to counter prosecution evidence in the current trial that some of the defendants and their associates were criminally conspiring as far back as Mr. Nosair's 1991 trial. Mr. Kunstler testified that the activities of these people during the 1991 trial had been legitimate, saying, for example, that Mr. Elgabrowny had worked as his paralegal during that trial. 
Mr. Kunstler slipped in some other points in as well, bringing admonitions from Judge Mukasey. For example, he several times steered his answers to note that Mr. Nosair had been acquitted of murder in the Kahane case in 1991 -- even though he was not asked the outcome of that trial. 
"Mr. Kunstler," the judge said testily, "the jury has been instructed that the verdict in the state trial has no weight in this trial, and yet you've mentioned it three times."