The city's judicial oversight commission, in a rare public censure, yesterday sternly criticized D.C. Superior Court Judge Joseph Michael Hannon for participating in an antiabortion march and raised questions about his presiding over a criminal trial that arose from the demonstration.

The D.C. Commission on Judicial Disabilities and Tenure said Hannon's decision this year to join in the March for Life Parade protesting the 1973 Supreme Court decision legalizing abortion showed "disapproval of the law which he and all other judicial officers are sworn to uphold." The panel said his conduct was "of a sort which erodes public confidence in the judiciary."

The two-page statement, signed by commission chairwoman Bette L. Catoe, said that Hannon's participation in the march violated the judicial canon that a judge should "respect and comply with the law" and act in a manner that "promotes public confidence in the integrity and impartiality of the judiciary."

Hannon agreed to permit disclosure of the statement, a move that avoided a formal hearing on his actions.

In the past decade, only two other Superior Court judges have been publicly criticized by the commission.

Hannon stunned a crowded courtroom in February when he disclosed -- shortly after the first witness had started testifying in the nonjury trial of seven antiabortion marchers -- that he and his law clerk had joined for several blocks in the Jan. 22 march that had ended at the Supreme Court with the arrests of the defendants before him.

Hannon, who announced that he opposed the court's Roe v. Wade ruling and was exercising his First Amendment right to protest, continued to preside over the case but withdrew the following day after media reports prompted questions about the propriety of his role.

The seven commission members said in yesterday's statement that although they could "make no determination as to whether as a matter of law" Hannon should have disqualified himself, the "better course would have been such disqualification . . . lest his conduct create an appearance of prejudgment or partiality, however unfounded."

The American Bar Association Code of Judicial Conduct, which is followed in Washington, says a "judge should disqualify himself in a proceeding in which his impartiality might reasonably be questioned."

Hannon, a member of the bench for the past 14 years, did not respond to a reporter's request for comment.

Hannon previously had discussed his failure to disclose his role in the march before the trial began, saying it was an "inadvertence" caused by a lapse in memory that he regretted. He said that "my heart of hearts is clear . . . that this court can remain absolutely and totally objective."

After Hannon withdrew, the case was assigned to Judge Carlisle E. Pratt, who is considering defense arguments that the demonstrators cannot be retried. The defense is saying that because the first trial had begun before Hannon withdrew, a second trial would violate the defendants' constitutional protection against double jeopardy.

Andrew Chopivsky, attorney for six of the seven defendants, said yesterday that the commission's ruling bolstered the argument that a second trial would be double jeopardy because it did not find that Hannon was required, "as a matter of law," to remove himself from the case.

Chopivsky disagreed with the commission's findings that Hannon acted improperly by walking in the march. "Anyone who knows Judge Hannon knows it would be foolish to even think that he would sway the result of the trial because of his personal opinion."

But the executive director of the National Abortion Rights Action League, who in a complaint with the commission sought Hannon's removal from the bench, called the commission's statements "an unambiguous censure."

"It is an important reaffirmation . . . that fairness, integrity and impartiality always must take precedence over personal ideology in the application of justice," said Kate Michelman.

The commission's statement praised Hannon's "record of integrity" and said that in light of his "exemplary judicial service" during his 14 years on the bench, no "charges or sanctions are warranted."

Hannon, 67, appointed by President Nixon, is regarded as a no-nonsense conservative.

In its statement, the commission said that it had met with Hannon, that he recognized that his conduct had "contravened" the Code of Judicial Conduct, and that he agreed to avoid such actions in the future.

The other two judges publicly criticized by the commission were Judge Nicholas S. Nunzio, reprimanded in 1978 for discourteous and impatient conduct during three criminal cases and for failing to "accord interested persons a right to be heard" in his court, and Judge Joseph M.F. Ryan Jr., criticized in 1983 after complaints that his conduct was "intemperate and injudicious" in dealing with people who had cases before him.