HARRISBURG, Pa. — A biochemistry professor who is a leading advocate of "intelligent design" testified yesterday that evolution alone can't explain complex biological processes and that he believes God is behind them.

Lehigh University professor Michael Behe was the first witness called by a school board that is requiring students to hear a statement about the intelligent-design concept in biology class. Lawyers for the Dover Area School Board began presenting their case yesterday in the landmark federal trial, which could decide whether intelligent design can be mentioned in public-school science classes as an alternative to the theory of evolution.

Behe, who wrote a 1996 best seller, "Darwin's Black Box," said students should be taught evolution because it's widely used in science and that "any well-educated student should understand it."

Behe, however, argues that evolution cannot fully explain the biological complexities of life, suggesting the work of an intelligent force.

The intelligent-design concept does not name the designer, although Behe, a Roman Catholic, testified he personally believes it to be God.

"I conclude that based on theological and philosophical and historical factors," he said.

The school board is defending its decision a year ago to require students to hear a statement on intelligent design before ninth-grade biology lessons on evolution. The statement says Charles Darwin's theory is "not a fact" and has inexplicable "gaps," and refers students to a textbook, "Of Pandas and People," for more information.

Behe contributed to "Of Pandas and People," writing a section about blood-clotting. He told a federal judge yesterday that in the book, he made a scientific argument that blood-clotting "is poorly explained by Darwinian processes but well explained by design."

Eight families sued to have intelligent design removed from the biology curriculum, contending the policy essentially promotes the Bible's view of creation and therefore violates the constitutional separation of church and state.

Mainstream scientists have rejected intelligent design as scientifically untestable and contend that its supporters focus on attacking evolutionary theory rather than providing evidence to support their views.

Behe, who was expected to resume testifying today, compared the outcry over intelligent design to the early criticism of the big-bang theory 70 years ago.

"Many people thought it had philosophical and even theological implications that they did not like," he said.

Lehigh's biology department sought to distance itself from Behe in August, posting a statement on its Web site that says the faculty "are unequivocal in their support of evolutionary theory." He earned tenure at Lehigh before becoming a proponent of intelligent design, which means he can express his views without the threat of losing his job.

In a related development yesterday, the Discovery Institute, a Seattle-based think tank that represents intelligent-design scholars, filed a brief urging U.S. District Judge John Jones to rule in favor of the school board.