In Private Practice, Roberts's Record Is Mixed

"It's good for lawyers to represent clients on all sides of the political spectrum," Olson said. "You can't read anything into his personal feelings about the case."

The Supreme Court hears only about 80 cases a year, so even elite appellate lawyers such as Roberts have to compete for cases, and they rarely turn them down. Olson said that Supreme Court specialists also regularly help less-experienced lawyers prepare as a professional courtesy. And Hogan & Hartson lawyers said the firm has a culture in which every partner and associate is expected to help out on pro bono cases when asked.

That is what happened in the Colorado gay rights case, Romer v. Evans , in which lawyers seeking to strike down the referendum sought the help of Hogan & Hartson. Walter Smith, then head of the firm's pro bono department, turned to Roberts for assistance. Smith said Roberts readily accepted, helping to grill the lawyers handling the case during a mock trial, in which he played the role of Justice Antonin Scalia. Roberts also helped devise a strategy for the case.

"He only put in a few hours, but a few hours with John Roberts is probably worth a few weeks with someone else," Smith said. "John was always willing to help on pro bono cases, regardless of the politics. Not all his conservative brethren felt that way."

On conservative Web sites yesterday, there was scattered negative reaction to the news that Bush's nominee had helped to advance the cause of gay rights. "Frankly, I find it hard to believe that a 'conservative' Roman Catholic would not have declined to participate on moral grounds," one person wrote at http://www.confirmthem.com/ .

John Yoo, a law professor at the University of California at Berkeley who served as a deputy assistant attorney general in the Bush administration, said the pro bono case was unusual for a conservative Republican lawyer. "Usually, conservative lawyers take on the more conservative causes," Yoo said.

On balance, the conservative establishment remained firmly supportive of Roberts. "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' personal views are reflected in his involvement in the case," the group Focus on the Family said in a statement.

David Leitch, a former Hogan & Hartson partner, said Roberts never brought politics into his practice.

"We were Republicans, no question about that," said Leitch, who is now the general counsel of the Ford Motor Co. "But I never knew John to turn down a case for ideological reasons. He was there to represent clients. And he did it very well."

Staff writer Peter Baker contributed to this report.