Creationism is back in the nation's public schools, brought in by fundamentalists who have traded their black preachers' hats for the white coats of scientists as they argue their case before school boards and state legislatures across the nation. The new costume is working.

On Tuesday, Louisiana became the second state to demand the teaching of creationism in its public school science classes, when Gov. Dave Treen signed a bill into law that requires teaching creationism in any classroom where evolution is taught. Arkansas voted a nearly identical bill into law earlier this year, and Georgia may join those two states in January.

And if the players on both sides have their way, this fall will be the hottest time for creationism in the United States since the summer of 1925, when John Scopes was convicted of teaching evolution in the famous "monkey trial" in Tennessee.

To encourage the growing tide of action across the country, the Rev. Jerry Falwell has just completed a national media casmpaign and now his Old Time Gospel Hour plans to stage a knockdown debate this fall between a creationist and an evolutionist -- 90 minutes on national prime-time television.

"We are billing it as the greatest thing since the Scopes trial," said Cal Thomas, speaking for the Old Time Gospel Hour. "It'll make great television; people can turn off the jigglies and the cop shows and turn on . . . a great debate."

At about the same time as the TV spectacular, a courtroom spectacular is scheduled for Little Rock, Ark., when the state will go to federal court to defend its new law.

All this and the tilt to the right in American politics is stirring action in local school districts across the country, where there is growing pressure to put the new "scientific creationism" into science classes.

The scientific creationists say that they have won their fight in local districts in virtually every state. The victories vary from adding disclaimers to textbooks and in teachers' lectures whenever evolution is mentioned, to the full-fledged teaching of creationism.

As President Reagan declared when he spoke out in favor of teaching the biblical story of creation in public schools, "Religious America is awakening."

In March, Arkansas became the first state to require that public schools teach creationism and evolution equally in science classes. The American Civil Liberties Union has sued the state to stop the law from being put into effect. The trial is scheduled to start Oct. 26, and ACLU lawyers promise a long list of stars among the scientists and religious leaders they will call to testify.

"We feel we are out to reposses out land," said Nell Seagraves, matriarch of the family that tried to get a court to declare that California had violated their 13-year-old child's rights by teaching him evolution. The Seagraveds family is one of the nation's engines of creationism. They head the Creation Science Research Center, which distributes literature and tactical advice to creationist groups.

"The naturalist-atheist-humanists are running things in this country," Seagraves said. "If you teach that man is an animal the way these evolutionists do, then there is no right and wrong and poeple will act like animals. . . . That is what happens when you divorce your curriculum from religion. We cannot live with chaotic values."

But Ashley Montagu, an anthropologist and author who used to be with the American Museum of Natural History, says that if the base of science is wrong, "I often wonder what these [creationist] people think of the Sabin and Salk vaccines, and the ability of science to abolish disease. Smallpox was one of the great scourges of the world, and it has been abolished. What do these people think of when they look at airplanes? All these things were arrived at in the same way as evolution."

"Absolute truth belongs only to one class of humans . . . the class of absolute fools," he declared. He said that the difference between science and creation-science is "that science has proofs without any certainty. Creationists have certainty without any proof."

It is unconstitutional to teach religious doctrine in public schools. Creationists acknowledge that their belief is religious and they speak about it that way among themselves, said Henry Morris, director of the Institute for Creation Research in San Diego.

But, he insists, "creationism is also scientific. In the schools that's the part we talk about. . . . That's not a tactic, that's our conviction."

Tactic or not, in recent years creationist literature and proposed bills have changed drastically. They no longer refer to Bible stories or God directly. Instead they speak of "the scientific evidences for creation," which are said to support "separate ancestry for man and apes . . . a worldwide flood . . . and a relatively recent inception of the earch and living kinds."

So far, this approach has successfully evaded the great historical barrier to teaching creationism in the schools: the First Amendment separation of church and state.

For example, the Oregon attorney general recently delivered an opinion that the "teaching of scientific creationism is allowed unless a particular course is found to constitute religious instruction."

Evolved over the past decade chiefly by the San Diego creationists, the new approach declares that the creation story is as valid scientifically as any other, because crationists simply can take traditional scientific evidence and reinterpret it to support creationism.

For example, methods of dating rocks and fossils back to ages of several billion years have been dismissed by creationists. They say that the radioactive decay that yields such dates could just as easily have started 10,000 years ago, with the Creator making rocks with already-reduced levels of radioactivity.

In at least 18 states, bills based on the "creation science" approach have been introduced during current legislative sessions. A similar bill, to stop lectures on evolution in national parks and museums, is expected to be introduced soon in the U.S. Congress.

A few cases in which creationists have gained with their new approach:

In a Tampa, Fla., school district with 115,000 children, the school board voted last spring to teach "creation science" equally alongside evolution in high school biology classes. A pilot program is scheduled in three high schools this fall.

In South Dakots, the state superintendent for instruction, Morris Magnuson, said he "did a quick survey by phone of schools in the state" and found that virtually all high schools make it a practice to include some commentary on creationism when evolution is brought up in science classes. s

In Minnesota, where there is no state policy on teaching evolution or creation, there are "hundreds" of teachers across the state who bring creationism into science classes, said Keith Hedges, a creationist. In Minnetonka High School, in a Minneapolis suburb, biology teacher Chares Bosacker says he will teach both creationism and evolution to his students, having successfully introduced the subject on a trial basis.

In Oregon, Dean Griffith, a former teacher and now leader of the state's leading creationist group, said that about a dozen local school districts have approved or demanded the teaching of creationism, together with evolution. Some accommodations have been made, ranging from putting creationist books in the library to asking teachers to explain creationism in some detail. In two areas, creationists are circulating petitions to put the issue on the ballot in a special election.

In Charleston, W. Va., creationism has been taught alongside evolution by vote of the county board of education.

In Texas, some school districts teach creationism alongside evolution. The state requires that science books clearly call evolution only one of several possible theories. Stickers to that effect must be put into books that contain references to evolution.

But in Cobb Country, Ga., an area won over by the "creation science" approach two years ago, the tactic backfired mightily after the school board passed a resolution to require the teaching of creationism in the schools. The board was pressed by "fire-breathing Biblical literalists," and assistant superintendent Stanley Wrinkle.

"There is no way a politician can vote against that kind of thing; it would be a vote against God. If you don't go along, you're a humanist and an atheist," he said. "But later we found out the resolution we passed was no local resolution at all. . . . Henry Morris [of the Institute for Creation Research in San Diego] wrote the resolution that . . . [was] passed off as something that came from our local community."

Added Wrinkle: "If that's truthfulness I've read the wrong 'Thou shalt not witness. . . .'"

The appearance of outside agitation was enough to get the board to vote "against God" the second time around, as they passed a resolution changing their directive and backing off from the mandatory teaching of creationism. Instead, the school district created a special optional course in "comparative theories of origins."

"There are more than 17,000 senior high school students, and fewer than a hundred even showed an interest in taking the course," Wrinkle said. "Twenty-four kids ended up in the course."

This year, the course has been abandoned for lack of interest.