WASHINGTON – Most conservative groups shrugged off the disclosure yesterday that President Bush’s Supreme Court nominee, Judge John Roberts Jr., helped gay rights advocates win a landmark 1996 high court ruling, though some prominent voices on the right said his role in the case was troubling and required further explanation.

While in private practice at a Washington firm, Hogan & Hartson, Judge Roberts volunteered to assist with the legal challenge to a Colorado ballot initiative that changed the state constitution to bar the enactment of any anti-discrimination protections for homosexuals.

By a vote of 6-3, the Supreme Court overturned the ballot measure, ruling that the state violated the equal protection clause of the Constitution by denying gays and lesbians the right to seek legislation that might aid their community. The ruling in Romer v. Evans was the first major victory at the high court for gay rights forces and is seen by scholars as the foundation for a 2003 decision that struck down anti-sodomy laws nationwide.

Judge Roberts did not argue the Colorado case nor does his name appear on the briefs, but he was vital to its outcome, according to other attorneys involved in the matter.

“What he did was take part in the strategizing of the case and working on the moot court,” a lawyer who oversaw pro bono work at Judge Roberts’s firm, Walter Smith Jr., said. “Just a few hours of John’s time was worth its weight in gold on this case.”

Judge Roberts’s duties included playing the role of conservative justices, such as Justice Scalia, who were expected to try to trip up the lawyer advancing the gay rights position. The future nominee’s involvement in the case was first reported yesterday by the Los Angeles Times.

Several conservative organizations that have been lobbying aggressively for the judge’s confirmation dismissed his limited work for the gay rights cause as inconsequential.

“He has sort of a servant heart,” the chairman of the Traditional Values Coalition, the Reverend Louis Sheldon, said. “My assessment is that Roberts had worked as a law clerk for Rehnquist and he was sort of the go-to lawyer. … I don’t think it’s anything for us to worry about.”

Rev. Sheldon, whose latest book is titled “The Agenda: The Homosexual Plan to Change America,” said he discussed the issue with others in the pro-Roberts camp and decided it was of no concern. “If the president is satisfied, I have to be satisfied,” the reverend said.

Another group, Focus on the Family Action, signaled that it was disappointed, but remained supportive of the nomination. “While this is certainly not welcome news to those of us who advocate for traditional values, it is by no means a given that John Roberts’s personal views are reflected in his involvement in this case,” the group, which was founded by broadcaster and psychologist James Dobson, said in a statement.

Concern about Judge Roberts’s role in the Colorado case was most pronounced yesterday on talk radio and on conservative Web sites.

“I do know that it is driving a wedge. It’s causing some curiosity and concern from people on the right,” the popular talk radio host, Rush Limbaugh, said on his program.

Mr. Limbaugh said Judge Roberts “worked to facilitate” a Supreme Court ruling that was a leading example of judicial excess. “This particular case, Romer v. Evans, actually threw out a ballot vote of the people of Colorado and then imposed the view of six justices on the issue of same-sex rights,” the radio personality said. “Once you start sanctioning a behavior as a civil right, then, you know, where do you stop?”

Mr. Limbaugh said repeatedly that the issue should be explored during the confirmation hearings, which are set to begin September 6. “The conservatives on this judiciary committee need to do their job, too,” he said. “There’s reason to ask him questions about this, especially in light of what he said in his questionnaire about the fact that [neither] the Supreme Court nor judges are to decide social issues.”

Some conservative lawyers said they were surprised by Judge Roberts’s role in the case. “If in fact he did this, this would be contrary to everything I’ve read about him thus far,” Mathew Staver, the president of a conservative legal group, Liberty Counsel, told the Baptist Press. “For the court to strike that down, I felt, was judicial activism.”

Mr. Smith, the lawyer who brought the matter to Judge Roberts, confirmed that he could have rejected it. “Pro bono matters are purely voluntary,” Mr. Smith said. “John had more discretion here to say, ‘No, this just is not for me,’ but he didn’t say that and I think that may be somewhat revealing.”

Mr. Smith, who has since left the firm, said he could not recall Judge Roberts ever rejecting a pro bono request. However, Mr. Smith added that he tailored his requests to avoid matters that might offend a particular lawyer. “There is a line a lawyer will not cross. A lawyer will not advocate things that are repugnant to him,” the former pro bono coordinator said.

A White House spokesman portrayed Judge Roberts’s role in the Colorado case as routine and minor. “His overall involvement in the matter was minimal, probably amounting to less than 10 hours,” the spokesman, Kenneth Lisaius, said. “It would be wrong to essentially equate legal work product with one’s personal opinion.”

Gay rights groups said they found the development intriguing. “Obviously, this work is supportive of our perspective and agenda on gay rights issues, but we don’t know what it means,” a spokesman for Lambda Legal, Michael Adams, said. “From our perspective, we balance it against a much more consistent record of advocating on behalf of positions we view as problematic.”

The president of a conservative women’s group, Phyllis Schlafly, said she wasn’t bothered much by Judge Roberts’s brief involvement in the gay rights case, but did draw some conclusions from it. “I guess it shows he’s not a Scalia. We were hoping to get a Scalia. Maybe he’s a Rehnquist,” Ms. Schlafly, who heads the Eagle Forum, said.