That gasp you hear, hissing and spitting from the direction of Cambridge, Mass., is the sound of a punctured taboo.

Thomas Penfield Jackson, like many a U.S. District judge before him, was amazed and angered by the outcome of a jury trial in his court. Unlike his more inhibited brethren, he said so -- in stark, dramatic language, with two newspaper reporters in the room.

A minor uproar has followed him back from Harvard Law School this week, the latest but probably not the last in the continuing legal drama surrounding Mayor Marion Barry.

What Jackson said Tuesday -- that there was "overwhelming" evidence of Barry's guilt, and that four of the mayor's jurors "obviously did not tell the truth" when asked if they could decide the case impartially -- continued to reverberate yesterday in Washington.

"Libelous. Slanderous. I think it's wrong," said R. Kenneth Mundy, the mayor's lead defender in last summer's trial. "The jury did exactly, and I wish you would publish this, exactly what they were told they could do . . . . The ones who held out for total acquittal did their duty no less than the others, because they followed their instructions to the letter."

Countered Stanley Sporkin, Jackson's fellow judge on U.S. District Court: "There's nothing that says the First Amendment applies to everyone but judges. Judges ought to be able to speak out at times and say how they feel about things. He said what he thought and he believes, and I think that's for him to do."

If Barry's case had been pending before him, legal ethicists said yesterday, Jackson's remarks to 200 students at Harvard's Criminal Justice Institute would have been a fairly clear breach of the Code of Judicial Conduct, a set of binding ethical rules. But last Friday's sentencing of the mayor -- and the notice of appeal that Barry filed the same day -- took the case out of Jackson's jurisdiction.

There was broad agreement yesterday that Jackson was free to say what he did. The controversy centered on a broader question of propriety and public policy: Is it desirable for judges to speak bluntly when they believe that justice miscarries in their courts?

Desirable or not, the practice is unusual in the prevailing judicial culture in Washington. The brouhaha over Jackson, in fact, turned in part on perceptions of decorum, as though he had booed the orchestra after a symphony.

One federal judge, upon hearing what Jackson said, shook his head and said only, "He shouldn't have done that." Others, even those who defended Jackson's right to speak as he did, said they would not have done it themselves.

"The public is ill-served by some of these taboos," said Martin R. Rosenthal, managing attorney of the program that brought Jackson to Harvard. "The entire justice system is grossly misunderstood by the public and, I would assert without being insulting, by the media. One reason for that is that the people with the most expertise in the justice system do a very poor job in explaining that system to the public."

Reid H. Weingarten, a former Justice Department prosecutor, agreed with Rosenthal and some other lawyers that "it's unusual and refreshing for a judge to express his views publicly."

Exactly how public Jackson intended to be could not be established with certainty. The forum at Harvard, though aimed primarily at law students, was open to the general public, and Mike Chmura, the law school's press liaison, told a Washington Post reporter about Jackson's appearance. Jackson, on the other hand, said Tuesday night that he did not know reporters were present until after his remarks were complete.

Where Jackson's defenders saw a useful educational purpose, his critics saw troubling implications in the judge's remarks.

NAACP leader Benjamin L. Hooks, who wrote a sentencing letter to Jackson on Barry's behalf, said he was most concerned about a potential taint on Barry's appeal. The three appellate judges who will hear the mayor's case, Hooks said, "will have heard what Judge Jackson said about it, and it's going to put them under the burden of trying to remove that from their minds."

Most critics focused on the impact of Jackson's remarks on the jury.

"I don't believe that anybody should comment at any point on what jurors did or didn't do," said Steven R. Kiersh, reflecting the views of several fellow defense lawyers. "If we want jurors to deliberate freely, they need to know that judges or lawyers or anybody are not going to comment on what they do. It's potentially intimidating to jurors, particularly in a high-profile case."

Jeffrey Hazard, who teaches judicial ethics at Yale Law School, emphasized the disparity of power between a federal judge and the citizens compelled to be jurors.

"These people were conscripted into doing their job," he said. "They're citizens. Our usual practice is not to criticize jurors even when you think they're wrong."

Jackson implied in his Harvard remarks, and some of his defenders made explicit, that there should be no such inhibition when a judge thinks jurors breach their oath to decide a case impartially. Citing a Washington Post reconstruction, published in August, of the jury's deliberations in the Barry trial, Jackson said it was clear to him that some jurors "had their own agendas.

"The jury is not a mini-democracy, or a mini-legislature," he said. "They are not to go back and do right as they see fit. That's anarchy. They are supposed to follow the law."