The federal government, seeking continued suppression of a Progressive magazine article on the workings of the hydrogen bomb, is contending for the first time that "technical information" revealing the secret of the weapon is exempt from the guarantee of freedom of the press in the First Amendment to the Constitution.

The contention marks a sharp change in emphasis in the case made by the government 5 1/2 months ago, when it persuaded a federal judge in Milwaukee to issue a preliminary injunction forbidding publication of "The H-Bomb Secret -- How We Got It, Why We're Telling It" by free-lancer Howard Morland.

At that time, the Justice Department -- and attorneys for the magazine, Morland, and editors Erwin Knoll and Samuel H. Day Jr. -- all stressed the fuling made in 1971 by the Supreme Court in the so-called Pentagon Papers case.

The court held that prior restraints on publication of protected speech come ot it with a "heavy burden" against their constitutional validity. In a key separate opinion, Justice Potter Stewart wrote that the government could not restrain publication of the papers because it hadn't shown that disclosure "will surely result in direct, immediate, and irreparable damage to our nation and its people."

In Milwaukee, the department contended, and U.S. District Court Judge Robert W. Warren agreed, that publication of the Morland article -- without deletion of 1,322 words claimed by the government to imperil national security -- would cause the kind of harm described by Stewart "by accelerating the capacity" of certain nations to make H-bombs.

After Warren rejected the defendants' please to lift the injunction, which he issued under the Atomic Energy Act of 1954, they appealed to the 7th U.S. Circuit Court of Appeals in Chicago. It has reserved 65 minutes for oral argument Sept. 13.

Under the Pentagon Papers standard, they asserted, the government has failed to prove the need for the injunction -- the first against press publication of political speech in the nation's history. That same theme dominates the joint brief filed in the appeals court several weeks ago by the American Civil Liberties Union, counsel for the editors, and the firm of White & Case, counsel for writer Morland.

But the government brief released yesterday after deletion of material considered to be secret, gives relatively short shrift -- seven of 123 pages -- to the constitutional prior restraint issue.

While renewing its previous arguments on the issue, the government unveiled its new assertion, saying that the First Amendment does not forbid it, in implementing the atomic energy law, "from restraining the publication of technical information disclosing the essential secrets of the most destructive weapon known to man."

A Justice Department spokesman declined to comment on the changed emphasis. "We can't discuss the brief out of court," he said. There was speculation that the change indicated concern in the department about the strength of its constitutional case.

Another shift in emphasis involves the section of the law under which the injunction was issued. The section forbids any person from communicating restricted data with "reason to believe" that the data will be used to injure the United States or to secure an advantage to any foreign nation.

In Milwaukee, as the new government brief acknowledges, its attorneys proceeded as if they were required to show that the defendants had reason to believe that publication would be adverse to the interests of the United States.

The government still contends -- and the defendants still deny -- that they had reason to believe. But the Justice Department now argues that reason to believe must be demonstrated only for a criminal violation. In the Progressive case, the department says, such a showing "is irrelevant in determining whether particular information, because of its nature, should be prevented from being shared with the world."

From the start of the case, Morland has said that he got all of his information for his article from public sources. Up to now, this hasn't been seriously challenged, although Deputy Assistant Attorney General Thomas S. Martin, in oral argument in Milwaukee, raised a slight -- and factually unsupported -- doubt.

The new brief takes a much harder line. At one point, for example, the government says: "The evidence suggests that Morland was able to write accurately about the H-bomb secret only because he had been given significant guidance by a person or persons with access to classified material."

At another point, the brief cites "Morland's lack of understanding of some of the concepts he describes, his unexplained decisions to use correct information and reject incorrect information from the same source, his admitted discussions with individuals who had access to classified information . . . "

Such observations are interrupted by large chunks of blank space resulting from deletions of material deemed by the government to be classified.

Asked for comment, Paul Friedman, a White & Case attorney representing Morland, said that he and the ACLU, in a reply brief, will denounce the government for "innuendo, speculation, and an unsupported personal attack." He said he also will say that the government was trying to shift to Morland the burden it must carry for seeking a prior restraint of publication.

By contrast with the defendants, the government denies that it seeks to restrain "political" speech, saying that they haven't articulated a "constitutionally protected interest" in the restricted material on nuclear weapons design that the government wants to strike from the article.

The defendants contend that if they can't print the disputed 1,322 words, they can't lay the necessary factual foundation and credibility for their argument that government-imposed secrecy about thermonuclear weaponry, not the article, imperils national security and the effort to prevent nuclear proliferation.

In all, about one-fifth of the government brief -- including 11 pages that are totally blank -- was deleted for security purposes.