In the hot summer of 1925, when William Jennings Bryan defended the old-time religion in the celebrated Scopes "monkey trial," fundamentalist politics was a powerful force. The "creationists" who believed in the literal accuracy of Genesis swept the teaching of evolution out of America's public schools.

Now, 55 years later Ronald Reagan has latched onto the issue again, with his recent endorsement of the modern fundamentalists and their revived creationist movement.

The new creationist movement is gaining increasing force. Bills demanding that the biblical version of creation be taught alongside the theory of evolution have been pushed in at least 15 states with some hope for victory.

Several states, including South Dakota, Wisconsin and Missouri, provide instruction on biblical creation as part of public school biology courses.

More important, textbooks from many of the major publishers have been revised under pressure to appease the creationists. At least one schoolbook devotes three pages to laying out in detail the creationist beliefs. Other texts now hedge on whether dinosaurs lived on earth millions of years ago, a point most scientists accept as proved. The creationists don't object to dinosaurs, but they insist that life couldn't have existed millions of years ago, because God created all life in six days only a few thousand years ago.

The revived movement is directly descended from the popular ferment of the 1920s, when John Scopes was convicted in Dayton, Tenn., and fined $100 for teaching evolution to school children. That movement, which regarded Charles Darwin's theory of evolution as blasphemy, succeeded in virtually eliminating the subject from American public schools from 1925 to 1963. Only in the last 20 years has evolution reappeared in texts in a major way. Now it is under serious attack again.

But the modern movement has a new strategy and a new name for itself -- "scientific creationism." The new approach includes recruiting scientists who are also fundamentalist Christians and arguing the issue with quotations from physicists and biochemists rather than from Genesis.

Duane Gish, a biochemist from the Institute for Creation Research, explains: "We believe we can argue the case against evolution purely scientifically. We may be fundamentalists, but we do not want to bring our brand of religion into the schools." His group, he says, merely wants equal consideration given to the "creation model" for the origin of man.

GOP presidential candidate Ronald Reagan raised the issue to the level of presidential politics recently at a meeting of evangelical Christians in Dallas when he claimed to see "great flaws" in the theory of evolution.

If evolution is taught in the public schools, he said, then "the biblical story of creation" should be taught alongside it. "Religious America is awakening," he said.

The head of the National Association of Biology Teachers, Wayne Moyer, calls the revival of creationism "an alarming reversion to the time of the Scopes trial."

"It is hard to know just how large the movement is now," said Dorothy Nelkin, a Cornell University scholar who has written a book on the movement. n"But you can take just this as your measure -- that in a hot political year one candidate has come out for this far-out issue, and his opponent in the White House is silent.

"Ten years ago that would have been an unimaginable situation. One thing it implies is that the [fundamentalist Christian movement] is powerful and going to get more powerful. Science is just one example, one area of life that is going to be affected.

"These people draw their legitimacy not from their arguments against evolution or against abortion but from the sounder concerns they raise -- about the state of the world, and about the fact that many people's real values are being challenged."

The traditional creationist doctrine holds that the universe and man were created by God 6,000 to 10,000 years ago. The universe and the creatures in it have not evolved at all, but were made just as they exist now.

Creationist beliefs conflict with scientific evidence not only in geology and anthropology, but also in physics, biology and astronomy.

Generally, scientists' reponses to creationism have varied from angry expostulation of the evidence to flippant humor.One scientist has suggested that biology should also give equal time to the stork theory of birth. Another wondered if the "equal time" argument requies a disclaimer in all copies of the Bible, stating that Genesis is only a theory, unsubstantiated by fact.

The new "scientific creationism" in the movement has come from the Institute for Creation Research, affiliated with the Christian Heritage College in San Diego. About a dozen scientists at the institute work full or part time on the issue.

Gish, associate director of the ICR, has a doctorate from the University of California at Berkeley, and he worked many years for the Upjohn pharmaceutical company.

Gish wants to put the theory of creationism on an equal basis with that of evolution, "because both are theories that are unverifiable. We cannot know about creation because we weren't there and neither were the geologists. Since nobody was there we have to make many assumptions. The underlying assumptions we dispute."

"Now it's true that scientific creationism is a theistic point of view. It requires the presence of an Almighty Creator," Gish said. "But nobody in the United States has the right to deny the possibility of the existence of God.

"In public schools the students should have the option of considering the theistic view or the atheistic view. Evolution, you see, is an atheistic theory."

Here are two of the major scientific arguments of the creationists:

First, they contend that, right after the "big bang" -- the cosmic explosion the scientists say created the universe -- the universe was "obviously in a state of great chaos" and that now the universe is "obviously in a highly ordered state."

Gish then cites the second law of thermodynamics, which states that in a closed system all natural processes tend to begin from a state of high energy and high order and then run down, becoming increasingly more chaotic.

The universe, which according to this law should have become even more chaotic after the "big bang," shows evidence instead of being highly ordered and complex, Gish said. This, he argues, means that God must be rescuing matter and life from running down into mere undifferentiated atoms in space.

Other scientists insist that the creationist argument misreads the first words of the second law of thermodynamics. It states that whole, closed systems must run down. The universe is a closed system and is running down, they argue; the solar system is a closed system and is running down.

But the Earth is only a part of the solar system, one that draws virtually all its energy from outside the Earth, from the sun. Thus, in tiny, local spots such as Earth, the second law of thermodynamics permits order, even life, to build up briefly as the larger system moves toward a cold death.

The second main argument put forward by scientific creationists contends that life could not have begun as the combination of chemicals in a primordial sea.

"If you take a simple protein, one that is made up of about a hundred amino acids in a chain," Gish said, "and given the fact that amino acids come in 20 different kinds, what is the probability of them coming together in one special ordered sequence?

"You find if you calculate the probabilities that there are so many different sequences possible, such an enormous number, that no chance process in five billion years or even 50 billion years could ever give a sufficient quantity of any special arrangement," Gish said.

Stephen Gould, a Harvard biologist, said this argument is similar to the old problem that posed this question: If a piano were smashed and all its keys scattered randomly in the sea, what would be the probability of the 88 keys coming again together in the right order?

"But unfortunately," Gould said, "Life is not like a piano. In real life, chemicals have strong affinities for one another. They have a gift for self-assembly."

Much of chemistry depends upon the ability of atoms and molecules to come together, drawn by electrical attraction, into special, useful assemblies. cIn fact, many of the components of life have self-assembled in test tube experiments.

Gould also confessed some irritation at evolution being called only a theory. "This is wrong," he argued. "Evolution is a fact, a fact as well established as apples falling down. The theory is a body of ideas explaining the fact of evolution."

There is dispute among scientists who study evolution, particularly since the fossil discoveries of Louis and Mary Leakey in Africa, over whether mankind evolved gradually from one species into another, as Darwin thought, or whether the evolution was relatively abrupt -- involving thousands of years rather than millions.

The fossil record suggests that human and animal species burst onto the scene and vanished in only thousands of years -- a view that creationists like to cite, as Gish does, "as a sign that the younger scientists are coming around to a view like the creationists'."

The new creationist movement got its first big political boost in California during the administration of Gov. Ronald Reagan. In 1969, a notably religious state board of education, with seven of 10 members appointed by Reagan, voted to accept a statement that creationism is a valid alternative to the theory of evolution.

The California board first approved the teaching of creationism side-by-side with evolution. Then, after much pressure from creationist scientists, the board decided instead to revise current biology textbooks to indicate that evolution is only a theory, and is no more verifiable than creationist doctrine.

Since the revision of biology books for California -- and those California texts were used all over the country in their revised form -- publishers, teachers and biologists have been battling the "equal time for creation" position in virtually every state.

One of the most respected of all biology texts, developed by the Biological Science Curriculum Study, is banned in Texas, because the book's authors refused to make any concessions to creationism.

"They asked us to stick in qualifiers all over the place, to make it a real wishy-washy book," said William Mayer, head of BSCS. "We said no."

Holt, Rinehart and Winston is one major publisher that has changed its textbooks to make them acceptable to state boards in such large markets as California and Texas.

"You can no longer have sentences like: 'Thirty million years ago the dinosaurs roamed the earth,'" said Paula Hartz of Holt, Rinehart. "There was no 30 million years ago for the creationists. So you may say, 'Some scientists have theorized that dinosaurs lived millions of years ago.'"

"Geologic ages are out," she said, "and Cro-Magnon man is out. All these things must be changed."

A spokesman for Houghton-Mifflin said that some states "look at the textbooks and then prescribe changes. 'This and this and this should be changed. "This line should go.'"

"And if you don't make the changes," he said, "don't bother to submit the books for use in their state."

"Texas and California are gigantic markets; you're talking about millions of dollars in book sales at stake," he said.

As an example of the kind of alterations being made in the textbooks, Dorothy Nelkin of Cornell cites the case of biology texts changed by publishers to accommodate California.

The California committee that screens books took particular care, she said, to remove all words implying the acceptance of evolution: they deleted the words "ancestors," descendants," and "origins." They added qualifying phrases such as, ". . . according to one particular point of view . . ."

Each section that discussed evolution was prefaced with a negative remark such as "science has no way of knowing how life began."

This sentence -- "Slowly, over millions of years, the dinosaurs died out," -- became "Slowly, the dinosaurs died out."

Paula Hartz of Holt, Rinehart, added that teachers' manuals, as well as textbooks, have changed. Teachers are now instructed that some children in their classes may hold creationist views. "'Do not challenge these views' is the best advice we can give now," Hartz said.

Publishers believe that soon one or more states will pass laws that require teaching the full creationist line alongside evolution. They also believe that some school systems already teach creationism without mention of evolution.

Hyde Post, a reporter for the Atlanta Journal, reported that in at least one public school in Walker County, Ga., a Baptist preacher takes over classes two hours a week to teach creation and take up a collection among the children.

Post said that, in Georgia, about two dozen resolutions pending before or already passed by local school boards would direct schools to teach some creationism.

"At the heart of all this," said Nelkin, "is a genuine concern among these people about values being relative. They want absolute values and cannot live with less.

"The movement scares me, not because it might affect science or the teaching of biology, but because it means the growth of intolerance, a new rigidity in values. That is dangerous."