In a rare ruling, a D.C. Superior Court judge declared a mistrial in a murder case yesterday because he said two of the three defense attorneys had failed to represent their clients effectively.

The move came with dramatic suddenness after three days of testimony in a case in which two brothers and a friend were charged with killing a 39-year-old construction worker in an incident outside a bar and grill at 9th and L Streets NW.

"You didn't try this case," Judge Nicholas S. Nunzio told the attorneys.

"You have succeeded in only one thing, and that is making me cognizant of my job up here and that is to ensure that they (the defendants) get a fair trial.

"My job is to see that they get a fair trial and they did not get a fair trial because of your actions."

Nunzio's remarks from the bench were directed at O. B. Parker, a veteran defense counsel in the criminal courts here and to Robert Liotta. Both had been appointed by the court to act as defense counsel and Nunzio fired them from the case.

He also said they would not be permitted to try major criminal cases in his courtroom in the future.

Court officials said such actions by Superior Court judges are rare, even though judges are frequently criticized for not insuring that indigent defendants receive better legal services. Under the federal criminal justice act, judges alone have the power to appoint lawyers to defend persons who are unable to hire counsel of their own.

The defendants in the case were Calvin Lewis Braxton, 22, Gene Arthur (Buster) Braxton, 28, and Darnell Lee Washington, 22. They are accused of murdering James Marshman, who was slashed and stabbed to death on the night of Oct. 10, 1975.

Parker, who represented Buster Braxton, declined to comment after Nunzio's ruling.

Liotta, who represented Washington, said he thought the ruling was "unfair" and added: "To grant a mistrial because of incompetent counsel was not the real reason. I think his comments about me were unfair."

Liotta said the frequent exchanges he had with Nunzio in the presence of the jury were the real reason the mistrial had been ordered. He said these exchanges were made necessary by Nunzio's refusal to allow him to conduct bench conferences on points of law. Bench conferences are held out of the hearing of juries.

Nunzio originally ordered that all three defendants be assigned new attorneys. He then ordered that Kenneth Trombly, who represented Calvin Braxton, remain on the case.

The judge's ruling came in the midst of closing arguments to the jury. He asked all three defense attorneys if they wanted a mistrial and all agreed. He then gave his reasons.

He made it clear that these reaons arose from Darnell Washington's testimony, which came yesterday morning. Washington testified that he had struck Marshman in the chest with a screwdriver in self defense. The blow caused a fatal wound.

Previously, Washington had told Parker, his attorney, that he had had nothing to do with the assault on Marshman. The change in Washington's story became apparent to Nunzio when Assistant U.S. Attorney Donald L. Abrams, the prosecutor, said to Washington: "You didn't even tell that to your attorney, did you?"

Nunzio then ordered the jury from the courtroom. He asked Parker if he had known about his client's convention that he had acted in self defense. Parker said he had not.

The judge said Parker was bound to report the change in his client's story to the court when the change occurred during Washington's testimony. This is in keeping with the canons of professional ethics. These canons state that attorneys must be able to vouch for the witnesses they call. If they have reason to believe a witness is lying they are bound to tell the judge. This is because the canons do not permit attorneys to argue to juries the truthfulness of testimony that they themselves may doubt.

Nunzio first ruled that Parker could continue in the case, but that he could not argue his client's self-defense story to the jury.

By the middle of the closing arguments, however, he had changed his mind.

It was understood that he felt that Parker could not effectively represent Washington because he could not argue the self-defense theory, and therefore Washington was denied his right to effective assistance by counsel.

The truthfulness of any testimony in a trial is a question for the jury to decide.

Nunzio stated repeatedly during the trial that Liotta was suggesting to the jury that the judge was "impeding" Liotta's case by ruling against him on questions of law. At one point he said he felt that he was "conducting a law school and that is not what I am here for."

The three defendants were returned to D.C. jail following Nunzio's ruling. No date for a new trial was set.