A federal judge said today that he will issue a secret opinion when he decides later this week whether to let the Progressive magazine publish a suppressed article on the workings of the hydrogen bomb.

In New York City, the chairman of the American Civil Liberties Union, which represents the magazine's editors, told a reporter that, to his knowledge, an in camera, or secret, opinion is "unprecedented."

Two other legal experts with whom he checked also knew of no precedent for a secret opinion, said Norman Dorsen, a constitutional law professor at New York University.

Another ACLU attorney said, however, that secret opinions have been issued on occasion. He said that one was issued only six months ago in a case involving the CIA.

U.S. District Court Judge Robert W. Warren confirmed through aides that he plans to make both his opinion and order secret, although he also many file a public version of the order.

Progressive editor Erwin Knoll told reporters, "As a defendent I find it intolerable to be subject to an opinion that I can't even read."

Knoll said he will ask his lawyers to decide whether to challenge the validity of the secret opinion in the 7th U.S. Circuit Court of Appeals in Chicago.

For more than two hours this morning, Warren heard arguments in his chambers on the ACLU's motion to lift the preliminary injunction he had granted March 26, at the government's request, to restrain publication of the article.

The injunction was the first in the nation's history to impose a prior restraint on material protected by the First Amendment to the Constitution.

The ACLU had filed the motion with the approval of the appeals court, which plans to hear arguments in September on the Progressive's effort to overturn Warren's injunction order.

In support of its motion here, the ACLU has provided Warren with recent evidence that the government, by erroneously declassifying documents on thermonuclear weapons, had for years made available information of a far more sensitive nature than any in the unpublished article.

Participating in today's argument were three lawyers for the government and eight for the magazine, its editors and Howard Morland, who wrote the article.