The American Civil Liberties Union and the National Rifle Association agree about very little. They are often on opposite sides in major cases, and they certainly have starkly different views about gun rights.

But when the Supreme Court agreed to hear the N.R.A.’s free-speech challenge to what it said were a New York official’s efforts to blacklist it, one of its lawyers had a bold idea. Why not ask the A.C.L.U. to represent it before the justices?

“The N.R.A. might be thought of as the 800-pound gorilla on the Second Amendment,” said the lawyer, William A. Brewer III. “Clearly, the A.C.L.U. is the 800-pound gorilla on the First Amendment.”

David Cole, the civil liberties group’s national legal director, said the request in one sense posed a hard question.

“It’s never easy to defend those with whom you disagree,” he said. “But the A.C.L.U. has long stood for the proposition that we may disagree with what you say but will defend to the death your right to say it.”

Mr. Cole’s group has been subject to occasional criticism that it has become less attentive to free-speech principles and more devoted to values rooted in equality in recent years. He rejected that critique, even as he acknowledged that the decision to represent the N.R.A. would not meet with universal praise.