The Arkansas creationism law was struck down yesterday in a broad and strongly worded ruling by federal Judge William Overton, who said the creationists themselves had admitted that the law "is a religious crusade coupled with a desire to conceal this fact."

The judge said that the law, which required that the so-called creation science be taught in schools where evolution was taught, violated the First Amendment clause against the establishment of religion by the state. He said that the creation science in the bill was not valid science and had no useful educational purpose, but served only to further religion.

"No group, no matter how large or small, may use the organs of government, of which the public schools are the most conspicuous and influential, to force its religious beliefs on others," Overton wrote.

The case was the first major court test of the idea of creation science, which says that there can be a scientific theory of creation which opposes the theory of evolution, and teaches tenets parallel to those in the Bible, but non-religiously.

If creationism could be shown to be scientific apart from its religious base, the creationists felt it could be introduced into the public schools to teach that Earth was created very recently and suddenly by God, and that all the creatures on Earth, including dinosaurs and man, were created at the same time, fully formed.

Using the idea of creationism as science, creationists got laws passed in Arkansas and Louisiana to support the teaching of their theory and got local school boards in virtually all states to accept teaching creationism or at least modify somewhat the teaching of evolution.

Bruce Ennis, director of the American Civil Liberties Union, which brought suit against the bill, said of yesterday's ruling, "This is a fatal blow to creation science. It states very clearly that creation science has no standing as science or education."

He said that another case challenging the almost identical law in Louisiana will be forced to the same conclusion because the law is the same, the witnesses will be largely the same, and the arguments made in favor of the law must be the same.

Richard Bliss, an officer of the Institute for Creation Research in San Diego, said of the decision, "This will be a blow to us . . . . Yes, we are discouraged, but not defeated."

He said the trial was a poor one because the judge "was very biased, and the attorney general of Arkansas, who argued for the law did not do his homework . . . . I think he was not competent to handle this kind of trial."

Bliss said he looks forward to the Louisiana case, in which attorneys from the institute will defend the Louisiana law. "If we don't win that one, I don't know what to say. We will have no excuse at all."

There is a traditional, three-part test set out by the Supreme Court to decide whether a law is unconstitutionally religious. Failing any one of the three parts can make the law unconstitutional.

Judge Overton said the Arkansas law fails on all three counts: It has a basically religious purpose; it has no secular educational purpose, and it would cause the state to get deeply entangled in religious judgments in trying to enforce the law.

After losing in court with their anti-evolution laws, the judge said, the fundamentalists changed their tactics and began to offer the biblical version of creation as science in hopes of establishing that in public schools.

The Arkansas law that came out of the fundamentalist, anti-evolution movement, the judge said, was one that "was simply and purely an effort to introduce the biblical version of creation into the public school curricula."

He said the definition of creation science in the bill "simply makes a bald assertion. It explains nothing and refers to no scientific fact or theory" to support the idea of a young Earth, an instant creation by God, and a single, worldwide flood that explains the world's geology.

The judge attacked the methods of the creationists, saying they "do not take data and weigh it against the opposing scientific data" to reach their conclusions. "Instead, they take the literal wording of the Book of Genesis and attempt to find scientific support for it," he said.