The Supreme Court ruled yesterday that juries in obscenity cases may suppress books, magazines or movies without being certain "beyond a reasonable doubt" that they are obscene.

The ruling, accompanied by three dissents, will make it easier for state and local governments and judges to move against what they consider obscene material.

Some First Amendment experts suggested that the ruling is of potentially major significance for future free expression controversies, although the court disposed of it in only four pages without hearing full arguments.

Yesterday's unsigned opinion stemmed from efforts by officials in Santa Ana, Calif., to suppress pornographic films at a theater there. During a trial, the jury viewed 17 films. When it came time to decide whether they were obscene, the judge told them that they had to be convinced "beyond a reasonable doubt" of the films' obscenity. That standard of proof is generally required only in criminal trials. Civil proceedings, as these were, require less certainty on the part of judges and juries because the penalties are less severe.

The Santa Ana jury thus found 11 of the films obscene and subject to suppression under local law. The city appealed unsuccessfully to the California Court of Appeal, which held suppression of material otherwise protected by the First Amendment required the strictest standard of proof.

The Supreme Court said yesterday it had never held that any civil case demands such a high standard of proof, and no special exception should be made for civil obscenity cases.

"While a state may require proof beyond reasonable doubt in an obscenity case, that choice is solely a matter of state law," the court said. The Constitution does "not require such a standard."

Justice John Paul Stevens said it was "distressing to find that the court considers novel questions of this character so easy as not even to merit argument . . . . The holding seems to rest on an assumption that, no matter what the consequences of a civil lawsuit may be, the Constitution does not require the plaintiff to satisfy the reasonable doubt standard of proof."

"If the court is endorsing that broad assumption today, then this decision is far more important" than it appears, he said.

Justices William J. Brennan and Thurgood Marshall also dissented, saying they believed the First Amendment requires the strict standard.