IN AN UNUSUALLY strongly worded opinion, Federal District Court Judge William Overton declared unconstitutional the Arkansas law requiring "balanced treatment" in the teaching of evolution and the biblical story of creation. In his ruling, Judge Overton flatly rejected claims by the law's supporters that there exists a valid "creation science." After hearing two weeks of testimony and examining the writings of those who drafted or promoted the new law, the judge concluded that the "evidence is overwhelming that both the purpose and effect of Act 590 is the advancement of religion in the public schools."

On many different grounds, the judge found so- called creation science to be not science, but camouflaged religion. A scientific theory, he wrote, is always tentative, its tenure subject to the discovery of new facts, whereas "a theory that is by its own terms dogmatic, absolutist and never subject to revision is not a scientific theory." The judge dismissed creationists' claims that they do in fact do scientific research but the results are suppressed by the scientific establishment; he noted that not a single witness had "produced a scientific article for which publication had been refused."

The Supreme Court has established three criteria for judging that a law violates the separation of church and state mandated by the First Amendment: that it serves no secular purpose, that it advances religion and that it causes excessive entanglement between church and state. Meeting any one of the three is grounds for declaring a law unconstitutional. Judge Overton's decision finds that the Arkansas law clearly fails on all three grounds. "Since creation science is not science," he writes, "the conclusion is inescapable that the only real effect of Act 590 is the advancement of religion." It would force teachers, school board members and other secular officials into making "delicate religious judgments" in evaluating texts and curricula.

The Arkansas decision is by no means the end of this chapter in American education. Legal tests-- the next will be in a few months in Louisiana--may continue until there is a final resolution by the Supreme Court. In fact, the forcefulness of the Arkansas decision may actually prompt an intensified effort by creationists. The Mississippi State Senate overwhelmingly passed a bill like Arkansas' within hours of Judge Overton's decision.

The real struggle, however, is being waged at the local level by parents, teachers, school board members and other citizens. They, in turn, powerfully influence textbook publishers, who determine what students will read. It is at this level that creationists have scored their greatest successes and that scientists and others interested in sound education have been most remiss.

There are encouraging signs that an opposition is at last beginning to organize to meet a threat it failed for too long to take seriously. The Arkansas ruling provides powerful support for these efforts. But it will be no substitute for them. In terms of determination, dedication and all the other elements that create political clout, the creationists are still ahead.