THE SUPREME COURT has now held, in Widmar v. Vincent, that the regulation of the University of Missouri forbidding the use of any of its facilities for religious meetings violated the free speech clause of the First Amendment and was unenforceable. The university had told a group of fundamentalist Christian students they could no longer use a campus room for their extracurricular meetings, which included prayer, hymn-singing and scriptural reading. The university continued to grant space to more than 100 other non-religious student organizations. Said the court: "The university has opened its facilities for use by student groups and the question is whether it can now exclude groups because of the content of their speech." The majority held 8-to-1 that this could not be done.

That strikes us as a good decision. But we are dismayed by a passing reference in Justice Byron White's lone dissent warning that the majority opinion will bring into question the court's long- held position that mandatory prayer in the nation's schools breaches the wall between church and state.

The new decision allows college students to meet voluntarily, on public property and on their own time, for religious discussion or prayer. The court, characterizing the university as an "open forum," based its decision on the right of equal access to that forum. In a footnote, Justice Lewis Powell emphasized that "young adults . . . are less impressionable than younger students and should be able to appreciate that the university's policy is one of neutrality toward religion."

Mandatory prayer in public schools attended by young children is quite different. Attendance at school through a certain age is compulsory. Undeniably, children are susceptible to peer pressure and the example of an authority figure, such as a grade school teacher. It is not enough to say that the 6-year-old can ask to be excused. Common sense and experience tell us he won't.

We don't agree with Justice White that this new decision calls into question all the earlier school prayer cases. Neither did his eight colleagues. The facts involved in this case, as distinguished from the school prayer cases of 20 years ago, are as different as youth and maturity, or compulsion and free choice. Our concern is that those who are organizing to overturn the school prayer cases may use the White dissent to legitimize their argument for reversing the earlier cases. We would guess that Justice White feared this would happen and raised a specter to persuade his colleagues that they were inviting trouble. We believe, however, the majority made a sensible decision. They know a firm stand from a slippery slope.