Denver ? A decade ago, John Roberts played a valuable role helping attorneys overturn a law that would have allowed discrimination against gays – pro bono work the Supreme Court nominee didn’t mention in a questionnaire he filled out for the Senate Judiciary Committee.

The revelation could dent his popularity among conservative groups and quell some of the opposition of liberal groups fearful he could help overturn landmark decisions such as Roe v. Wade, which guarantees a right to an abortion.

An attorney who worked with Roberts cautioned against making guesses about his personal views based on his involvement in the Colorado case, which gay rights advocates consider one of their most important legal victories.

“It may be that John and others didn’t see this case as a gay-rights case,” said Walter Smith, who was in charge of pro bono work at Roberts’ former Washington law firm, Hogan & Hartson.

The case involved Amendment 2, a constitutional amendment approved by Colorado voters in 1992 that would have barred laws, ordinances or regulations protecting gays from discrimination by landlords, employers or public agencies such as school districts.

Gay rights groups sued and the law was declared unconstitutional in a 6-3 ruling by the U.S. Supreme Court in 1996.

Roberts’ role in the case, disclosed this week by the Los Angeles Times, included helping develop a strategy and firing tough questions at Jean Dubofsky, a former Colorado Supreme Court justice who argued the case, during a mock court session, Smith said.

Dubofsky, who did not return calls Friday, said Roberts helped develop the strategy that the law violated the equal protection clause in the Constitution – and prepared her for tough questions from conservative members of the court.

Smith said any lawyer at Hogan & Hartson would have had the right to decline to work on any case for moral, religious or other reasons.

“If John had felt that way about this case, given that he is a brilliant lawyer, he would have just said ‘This isn’t my cup of tea’ and I would have said ‘Fine, we’ll look for something else that would suit you,'” Smith said.