HARRISBURG, Pa. — Steven Stough was stunned when his school board decided to require ninth-grade biology students to learn about alternatives to the theory of evolution.

What bothered him was the Dover Area School District's mandate for the teaching of "intelligent design," which holds that the universe is so complex that it must have been created by some higher power.

Stough, 49, agrees with critics who say the concept is really a more secular form of creationism, a biblical-based view that credits the origin of species to God. He does not want his eighth-grade daughter to have to learn about it in high school next year. Stough and seven other families filed a federal lawsuit yesterday alleging that the district's new science curriculum violates the constitutional separation of church and state.

"My initial thought was, this couldn't possibly happen, and little by little, that opinion changed," Stough said following a news conference in Harrisburg. "I just felt it had no place in the science curriculum."

The lawsuit was filed on behalf of the families by the state American Civil Liberties Union chapter and Americans United for the Separation of Church and State. Both groups said the lawsuit was the first in the nation to challenge whether public schools should teach intelligent design, representing the newest chapter in a history of evolution litigation dating back to the Scopes Monkey Trial in Tennessee nearly 80 years ago.

"Since then, the courts have made it very clear that you cannot teach the biblical story of creation as science," said Witold Walczak, the ACLU's legal director, citing the 1987 U.S. Supreme Court decision Edwards v. Aguillard, which struck down a Louisiana law requiring that any public school teaching evolution must also teach "creation science." "Intelligent design is a Trojan horse for bringing religious creationism back into the public science classroom."

The Dover Area School District was believed to be the first in the nation to mandate the instruction of intelligent design when it voted 6-3 on Oct. 18 in favor of including the concept in the science curriculum.

The Rev. Barry W. Lynn, executive director of Americans United, characterized the vote as part of a "misguided crusade" against science education in public schools.

"Intelligent design has about as much to do with science as reality television has to do with reality," Lynn said.

School district officials had no immediate comment on the lawsuit. Administrators have declined to discuss the mandate, which applies to ninth-grade biology classes at Dover High School.

School board member William Buckingham, who spearheaded the change as the leader of the board's curriculum committee, has said he proposed the change as a way to balance evolution with competing theories that question its scientific validity. He did not return a telephone call seeking comment for this story.

At least one other district has recently become embroiled in federal litigation over teaching evolution. A federal judge in Georgia is considering the constitutionality of a suburban Atlanta district's decision to include a warning sticker about evolution on biology textbooks.

Last month, the Dover school district issued a statement saying that state academic standards require the teaching of evolution, which holds that Earth is billions of years old and that life forms developed over millions of years. The statement also said Charles Darwin's theory "is still being tested as new evidence is discovered," and that intelligent design "is an explanation of the origins of life that differs from Darwin's view."

Additionally, district officials said they would monitor the lessons "to make sure no one is promoting but also not inhibiting religion."

Biology teachers are expected to discuss evolution sometime next month, but Eric Rothschild, an attorney with a Philadelphia law firm involved in the lawsuit, said he hoped the school board would act quickly to rescind the intelligent-design mandate.

Two of the three dissenting board members have resigned in protest. Angie Yingling, a board member who originally voted for the policy, also announced during a Dec. 6 board meeting that she intended to resign after she was unable to get the board to reconsider its decision.

Yingling said yesterday that she had supported a provision of the policy that enables the high school to use an intelligent-design textbook as a reference book, but not the mandate to teach intelligent design.

"Anyone with half a brain should have known we were going to be sued," she said. "You can't do this."