NEW YORK, April 15 (Reuters) - Supporters of California's Proposition 8 banning gay marriage are claiming that the federal judge who struck down the ban violated his own court's rules by showing a video clip from the procedings during a public lecture. In a motion filed in the 9th Circuit Court of Appeals, Prop 8 backers demand that Vaughn Walker stop airing the video and that he hand over all copies of any recordings of the trial.

Walker, who has stepped down from the bench, showed a clip from the trial on Feb. 18 to students at the University of Arizona, during a lecture on the history of cameras in the courtroom. He has called the recording "part of the public record."

The subject of video cameras emerged as a major point of contention during the Prop 8 trial last year. Those in favor of gay marriage wanted the proceedings to be videotaped, as did a collection of media organizations. Opponents of gay marriage sought to block it, saying it would deter witnesses from testifying.

Walker himself wanted the trial recorded: He had just begun a program to videotape some trials. But gay-marriage opponents appealed, and the U.S. Supreme Court ordered a halt to the program, saying it had been established "in haste." Walker said he would honor the stay and that he would record the trial simply for his own purposes -- to review the record to aid him in deciding the case. The recordings were filed under seal.

In their filing on Wednesday, gay-marriage opponents said Walker violated his court order and local rules governing the federal courts in San Francisco, and that he defied the Supreme Court's order. Walker should be "ordered to cease further unlawful and improper disclosures of the trial recordings" and should return tapes in his possession, the filing said.

FIRST-AMENDMENT QUESTION

Walker's 42-minute lecture in Arizona included footage from the Lindbergh kidnapping trial and other trials where cameras were allowed in the courtroom. At the end of the lecture, Walker played a three-minute clip from the Prop 8 trial -- a cross-examination by David Boies, who represented gay-marriage supporters.

The gay-marriage opponents' motion raises an interesting First Amendment question, Professor Wilson Huhn of the University of Akron School of Law said in an interview. "Does the public have a right to this information," Huhn said, "even though there is a court order against disseminating this?"

The coalition representing supporters of gay marriage framed the legal question in terms of public access. "Why should the public be denied the opportunity to see and hear what happened in a public trial in a public courtroom in a case involving the constitutional rights of millions of people?" said Theodore Boutrous of Gibson Dunn & Crutcher, another lawyer for gay-marriage supporters.

Walker declined to comment to Reuters Legal. In a letter to the 9th Circuit on Thursday, Walker seemed to acknowledge the ethical issues.

"If the court believes that my possession of the videos as part of my judicial papers is inappropriate, I shall, of course, abide by that or any other directive the court makes," Walker wrote.

The 9th Circuit must still rule on gay-marriage opponents' appeal of Walker's ruling. Oral arguments in the case, which were conducted in December, were shown live on C-Span.

Walker has used the recording in several speeches and plans to use it in a presentation next week at Gonzaga University Law School, according to his letter to the 9th Circuit.

The appellate case is Perry v. Brown, 9th Circuit Court of Appeals, No. 10-16696.

(Reporting by Carlyn Kolker of Reuters Legal; additional reporting by Dan Levine of Reuters)