The Supreme Court ruled yesterday that public colleges and universities may not prevent campus organizations from conducting religious services on campus, even though it means that state-financed facilities are used to benefit religion.

In an 8-to-1 decision in one of the most important church-state cases of recent years, the justices struck down a University of Missouri ban on organized prayer and Bible reading at its Kansas City campus.

Justice Lewis F. Powell Jr., writing for the majority, said that a ban on religious worship and prayer is a ban on free speech. Universities are public forums, he said, and may not prohibit one form of expression while allowing all others.

While yesterday's decision does not alter the ban on prayer in public secondary and elementary schools imposed by the court in the 1960s, it undoubtedly will fuel the currently intense debate over those earlier rulings. The lone dissenter yesterday, Justice Byron R. White, expressed concern that "all of these cases would have to be reconsidered" under the majority's reasoning yesterday.

The court has always treated universities differently from grade schools, where pupils are believed to be of an "impressionable" age.

Most public universities already permit prayer and religious worship in their facilities. Had the court upheld the Missouri ban, imposed because officials there thought a permissive policy amounted to state sponsorship of religion, the other schools would have been forced to rethink their policies. That likely would have led to objections from state legislators, and the Supreme Court might have found itself once again embroiled in a major political controversy. The University of Missouri at Kansas City officially recognizes more than 100 student organizations and routinely provides facilities for their use. Among those groups was Cornerstone, a Christian organization that had been freely using facilities from 1973 to 1977. In 1977, however, the university told the group that its meetings, which regularly included prayer and Bible reading, would no longer be permitted.

University officials contended that they had no choice but to ban the group. Allowing Cornerstone's activities on the taxpayer-financed campus, they said, amounted to an "establishment" of religion, forbidden by the First Amendment to the Constitution.

The students argued, under the standard grounds for such challenges, that the ban infringed their right to the free exercise of religion. But they also contended that religious worship was a form of speech and therefore entitled to the free speech protections of the First Amendment. That has not been so clear in prior Supreme Court rulings.

Yesterday, upholding the 8th U.S. Circuit Court of Appeals in Widmar vs. Vincent, Powell agreed with the students.

"The University of Missouri has discriminated against student groups and speakers based on their desire to use a generally open forum to engage in religious worship and discussion," Powell said. "These are forms of speech and association protected by the First Amendment."

Speech may not be regulated or banned because somebody doesn't like its content, he said. The university did just that by differentiating between "religious speech" and, for example, political speech.

" . . . Having created a forum generally open to student groups," Powell said, "the university seeks to enforce a content-based exclusion of religious speech. Its exclusionary policy violates the fundamental principle that a state regulation of speech should be content-neutral and the university is unable to justify this violation under applicable constitutional standards."

The university, citing the court's justifications for banning prayers in grade schools, had contended that allowing Cornerstone's worship would amount to state sponsorship of religion.

Powell disagreed. "An open forum in a public university does not confer any imprimatur of state approval on religious sects or practices," he said, any more than allowing the Young Socialist Alliance meetings gives state approval to socialism. Any benefit conferred on religion by permitting Cornerstone's worship is "incidental," Powell said, quoting a prior court ruling that if the Constitution barred general benefits to religious groups " 'a church could not be protected by the police and fire departments or have its public sidewalk kept in repair.' "

Justice John Paul Stevens, in a concurring opinion, agreed that the ban was impermissible, but he gave different reasons than Powell. The university simply had no valid reason for banning the group, Stevens said, and he said the majority went too far when it said the university could not make decisions based on the content of speech on its campus. White, in his dissent, said the proposition that religious worship is no different from any other form of expression is "plainly wrong."

"Were it right, the religion clauses of the First Amendment would be emptied of any independent meaning in circumstances in which religious practice took the form of speech."

If the majority "were right that no distinction may be drawn between verbal acts of worship and other verbal acts," he said, all of the cases concerning religious worship in public institutions would have to be reconsidered.

Among the cases cited by White was one banning prayer in public grade schools, a ruling conservatives are now trying to reverse through Congress, in bills stripping the courts of certain powers.

In a footnote the majority opinion noted that unlike grade school children, "university students are, of course, young adults. They are less impressionable than younger students and should be able to appreciate that the university's policy is one of neutrality toward religion."

Powell and church-state experts interviewed yesterday also said that grade schools have never been considered "public forums" for expression of political views.

In addition, university clubs do not require supervision by teachers as do activities in elementary and high schools. The courts have held that that supervision could create the impression in younger children that they had an obligation to participate in prayer or that the school was endorsing the religious worship.