The Supreme Court ruled yesterday that The Nation magazine violated federal copyright laws when it scooped Time magazine and printed excerpts of former president Gerald R. Ford's memoirs before the book's publication in 1979.

In a 6-to-3 decision written by Justice Sandra Day O'Connor, the court said the liberal weekly "went beyond simply reporting copyrightable information." The magazine engaged in "piracy of verbatim quotations" for profit, she said, and used a "purloined manuscript" to do so.

The Nation received a manuscript from a still-unidentified source and printed excerpts two weeks before Time was scheduled to do so. As a result, Time canceled its contract with the book's publishers and withheld $12,500 it had agreed to pay. Under yesterday's ruling, The Nation likely will have to pay that amount to Ford's publishers, Harper & Row and Reader's Digest.

The Nation, which published key portions of the book dealing with Ford's pardon of his predecessor, Richard M. Nixon, severely diminished the market value of the work, O'Connor wrote.

The majority rejected the magazine's arguments that it was reporting news, that the Nixon pardon and other issues were matters of broad public concern, and that its use of about 300 words from the 200,000-word book was permissible under the "fair use" exceptions in the 1976 federal copyright law.

Yesterday's ruling was the court's first attempt to weigh constitutional protections for speech and the press against the copyright law's somewhat ambiguous "fair use" exceptions.

Those exceptions are generally reserved for scholars, book reviewers, biographers and other writers to protect them from the copyright laws even when they repeat substantial portions of another author's words.

The Nation's arguments, O'Connor said, "would expand the fair use exceptions to effectively destroy any expectation of copyright protection in the work of a public figure." In a key portion of the ruling, she said exceptions to copyright laws should be narrower in instances such as this, where the work had not been published, than for published works.

That view of the federal law, Justice William J. Brennan Jr. said in dissent, was "unwarranted on its own terms and unfaithful to congressional intent."

Brennan, joined by Justices Byron R. White and Thurgood Marshall, said the ruling "permits Harper & Row to monopolize information."

"This holding effects an important extension of property rights and a corresponding curtailment in the free use of knowledge and of ideas," Brennan said. "The Nation was providing the grist for . . . robust debate" of public issues, he said, but the court majority was penalizing the magazine "for no other reason" than that it was first to publish.

Lawyers for The Nation and other publications predicted more litigation and efforts to change the law as a result of yesterday's ruling. Benjamin W. Heineman Jr., an attorney who represented several newspapers in the case, including The Washington Post, said the decision "invites subjective interpretations" by the judiciary and will likely lead to further litigation.

Floyd Abrams, who represented The Nation, said the decision could mean "denial to the public of information about the most important decisions of their government unless and until it is sold to them for profit by a former government official." Abrams said the decision is likely to lead to congressional reconsideration of the 1976 law.

But William Patry, an attorney representing the book-publishing industry, said the decision accurately reflects congressional intent in passing the 1976 law. "It's not accurate to put up the First Amendment on one side and copyright law on the other," he said. Yesterday's ruling emphasized that the 1976 law was in the public's interest, he said, in that it ensured increased availability of creative works.

In other action yesterday, the court:

Agreed for the second time this year to hear a case involving the right to abortion.

The justices agreed last month to consider a case from Pennsylvania. Yesterday they agreed to hear appeals by Illinois officials and doctors who argue that a state law regulating abortion and certain methods of birth control is constitutional. The case, Diamond v. Charles, will be argued next fall in tandem with the Pennsylvania case.

Declined to hear an appeal by the Chicago Board of Education that the Reagan administration should help pay for integrating the city's schools. The case is Board of Education of Chicago v. U.S.