The creationist movement in America--riding high with two new state laws and an endorsement from Ronald Reagan--faces its greatest challenge in recent times, at a modern-day "Scopes trial" to test whether creationism can be taught as science in public schools.

On trial, beginning here Monday, is a creationist-drafted "model bill" requiring that when public schools teach evolution, they also teach creationism.

If the law survives this first court test and is declared constitutional, "I think every state in the union will pass a creationist law immediately," said its sponsor, Arkansas state Sen. Jim Holsted. If the creationists fail, the going may get tougher in school boards, legislatures, and other courts.

For creationists, the trial will also be a confrontation with an old enemy: the American Civil Liberties Union. Back in 1925, it was the ACLU that recruited lawyer Clarence Darrow to defend school teacher John T. Scopes for teaching evolution in Dayton, Tenn. Scopes lost in that celebrated "monkey trial," and teaching of evolution was set back for decades.

In the Arkansas case, the ACLU sees a thinly disguised attempt to put religion, and a fundamentalist brand of it, into the public schools under the description of "creation science."

The Arkansas law defines "creation science" as the idea that the world and all its creatures were created by a supernatural event, all at once, a very short time ago. This is contrary to the tenets of mainstream geology, physics, astronomy, and biology. The law also calls for teaching about the occurrence of a worldwide flood like the one weathered by Noah and his ark.

Police and the courts in Little Rock are preparing for large crowds at the trial, and possible demonstrations as well. Reporters from all over the country and from some international organizations have poured into Little Rock, and local television stations are putting on special broadcasts.

For Arkansas Attorney General Steve Clark, who will direct the state's defense, "It's the lawsuit of a lifetime from a lawyer's point of view."

Attorneys for the two sides have lists containing the names of more than 60 scientists, philosophers and theologians who are ready to testify.

The act became law last March 19. A nearly identical law was passed in Louisiana last summer, and similar bills have been introduced in at least 18 states. Creationists also have claimed victories at local schools, from the addition of disclaimers in science books to the full-fledged teaching of creationism.

Adding to the creationists' momentum was Reagan's statement to a group of fundamentalist leaders just before his election as president that he favored teaching the biblical story of creation in public school. "Religious America is awakening," he said.

According to pretrial briefs, the trial will turn on the question of whether "creation science," as it is called in the law, can be proven to be religion and not science.

The state's brief concedes similarities between the law's definition of "creation science" and biblical teachings. But the state defends the law as nonreligious, saying, "The mere coincidence of a governmental program with the beliefs of some religions does not entangle the state with religion."

"God is not on trial," said Clark. "Some people think if you say creation, if you say creator, it's God, a god of some form or shape. We're saying to the court, the concept of a creator is not an inherently religious idea."

In a pretrial hearing, U.S. District Judge William Overton, who will preside at the trial and decide it without a jury, asked lawyers for the state about this claim. If creation science "doesn't require belief in a creator, what do you teach in biology class? What do you tell them spawned the sudden creation? "

The creation might be attributed to a supernatural power without reference to God, the lawyers replied.

The ACLU brief counters: "Even if some of its minor premises look, smell, taste, feel, and sound scientific, its major premise--God --is not subject to testing or to disproof and, accordingly, is not scientific."

"Over a long period of time, the fundamentalists have used various tactics to get their religious beliefs put into public schools. The latest one is calling them 'creation science,' " said Jack Novik, assistant director in the ACLU national office. "In the monkey law fought over in the Scopes trial , they tried to exclude evolution from the schools. Now, they're going to leave evolution in place but give, put their religious views in alongside it."

To the ACLU, the ironic parallels of this trial and the Scopes "monkey trial" are evident. When the ACLU filed suit in May against the Arkansas law, the ACLU's founder, Roger Baldwin, said he had the feeling, "Here's where I came in." Baldwin, who died in August, recruited Scopes and his attorney, Darrow, for the original test case.

The "monkey law" in that case forbade anyone "to teach any theory that denies the story of the Divine Creation of man as taught in the Bible, and to teach instead that man is descended from a lower order of animals."

In a classic confrontation between Darrow and the most famous of creationists, the orator and politician William Jennings Bryan, Scopes and the ACLU lost. Scopes was fined $100, and evolution was virtually wiped out of public school texts from that time until the 1960s. The law was later repealed.

In 1929, Arkansas passed an anti-evolution law with softer wording and a less blatantly religious character. The law stood until 1966 when the creationists and the ACLU met for another round, called Epperson vs. Arkansas. That law was careful not to mention God, saying instead only that it was illegal to teach the "doctrine that mankind ascended or descended from a lower order of animals."

Caution didn't help in that case; the law was stricken from the books by the U.S. Supreme Court because it amounted to the establishment of a state preference for one religion over another.

In this battle, the law presented by the creationists does not mention God but only implies a creator.

Creationists believe they have a good chance of winning this case, said Holsted.

"But if we lose it won't matter that much. If the law is unconstitutional it'll be because of something in the language that's wrong," he said. "So we'll just change the wording and try again with another bill . . . . We got a lot of time. Eventually we'll get one that's constitutional."