Washington — If you look for the word ''evolution'' in the index of a new high school textbook, ''Experiences in Biology,'' you won't find it. The reason is simple. The publisher instructed the authors to include the concept, but not the word.
Why? ''Because it's a volatile issue at the present point,'' explains Eugene R. Frank, director of publication for the book's publisher, Laidlaw Brothers, a division of Doubleday.
Such shying away from evolution is growing more common in science education as the battle between the ''creationists'' and natural scientists escalates. The center stage is a federal courtroom in Little Rock, Ark., where the two sides are fighting over a state law requiring schools to give equal treatment to both evolution and ''creation-science.''
The Arkansas law orders that schools next fall give ''balanced treatment'' to the theory of a ''sudden creation of the universe,'' including ''separate ancestry for man and apes'' and an explanation of the Earth's geology in part by ''the occurrence of a worldwide flood.''
Science teachers and some church leaders who are challenging the law charge that it is a blatant attempt to put religious doctrine in the classroom and that it will damage education.
''Creationists'' counter that teaching their theories would only be fair, since they say that ''evolution'' is itself a type of religion.
''Your origins have to be based on somebody's philosophy, somebody's religion ,'' says creationist Mel Gabler, who with his wife Norma runs Education Research Analysts Inc., out of their Longview, Texas, home. For 20 years they have been scouring through textbooks looking for biases against their conservative, fundamentalist viewpoint.
Science teachers who evade the question of a creator or who call the universe self-existent are promoting a ''no God religion,'' says Mr. Gabler. He asserts that educators can teach scientific evidence pointing to a creationist view without going into religion.
Wayne A. Moyer, a Princeton University-trained biologist who heads the National Association of Biology Teachers, rejects that view. ''They are proposing that we teach a religious point of view in science classes as though it was science,'' he says.
If the creationists are successful, he predicts that scientific research could be set back.
''Competent science teachers are going to be questioning whether they ought to stay in science education,'' he says. ''Educators are going to be asked to stand in front of students and say that all animals and plants and the world were created 6,000 years ago, and that a great flood covered the entire world, even the highest mountains, and hollowed out the Grand Canyon in one year.''
Dr. Moyer, whose 6,000-member organization is one of those challenging the Arkansas law, holds that ''common sense'' will prevail and that the creationists will lose in the long run. But Moyer and others concede that fundamentalists have already made headway, no matter how the Arkansas case ends.
In some cases evolution, or natural selection, is not well taught, says Moyer , who adds that he spends about 20 percent of his time dealing with the controversy.
Creationist Mel Gabler agrees that some changes have already come. He says that he was pleased to note that of a group of new junior high texts, three had little mention of evolution. He says of publishers, ''I think they have modified their stand to some extent.'' He gives credit in part to a California lawsuit last spring, which gave a partial victory to creationists.
Gerald Skoog, professor of secondary education at Texas Tech University, has made a careful study of science texts' coverage of evolution and finds it shrinking. The 1960s brought a major effort to upgrade science education, in the wake of the Soviet Union's surprise launching of the first Sputnik satellite, recalls Skoog. As one result, biology texts suddenly began placing a heavy emphasis on evolution.
''This brought the antievolutionists out in force,'' he says. ''During the 1970s there was a slight decline in coverage of evolution in quantity and some subtle changes in wording and some not-so-subtle changes in wording.''
The Laidlaw book which avoids all use of the term evolution is one example. Also, Prentice-Hall Inc. has recently published ''Biological Science,'' which groups the discussion of natural selection, or evolution, in the last few pages. ''In that particular book, it was not a direct attempt to downplay evolution,'' says a company spokesman. But critics point out that such treatment makes it easier to skip the thorny issue.
Meanwhile, in scattered districts, school boards are ordering texts put out by creationists. Creation Life Publishers in San Diego reports that it sold 25, 000 biology books last year teaching both creation and evolution and that as many as one-fourth went to public schools.