In the gay community, though, conspiracy theories initially abounded that Mr. Olson had taken the case to sabotage it. While many have since come around, fears remain that a loss in the closely divided Supreme Court could deal a setback to the movement.

Opponents have flooded Mr. Olson with accusatory and sometimes hate-filled e-mail. “A disgraceful betrayal of the legal principles you purported to stand for,” read one message. “Homo” read another.

Conservative colleagues are kinder, but many remain bewildered. Former Judge Robert H. Bork, a close friend who has called same-sex marriage a “judicial sin,” said he could not bear to speak to Mr. Olson about the case.

“I don’t want to get into an argument,” Mr. Bork said. “But I’d like to know why.”