Charles Darwin's theory of evolution came under sustained attack in federal court here Monday as biochemistry professor Michael J. Behe argued that the theory fails to account for the complex biological machinery that scientists find in the corners of the human cell.

Behe, who teaches at Lehigh University, is one of the intellectual founding fathers of "intelligent design," which holds that aspects of life are so complex as to be best explained as the work of a super-intelligent designer.

"The appearance of design in aspects of biology is overwhelming," Behe told the court. "Intelligent design is based on observed, empirical, physical evidence from nature."

Behe is the lead defense witness in a trial that has drawn national attention since it began three weeks ago. Last year, the school board in Dover, Pa. -- a small town south of Harrisburg -- voted to require high school biology teachers to read to students four paragraphs that cast doubt on Darwin's theory of evolution and say that intelligent design offers an alternative theory for the origin and development of life.

Eleven parents sued to block the school board's action. The parents' lawyers, along with prominent scientists and philosophers, have argued that intelligent design is biblical creationism draped in new clothing. They note that the U.S. Supreme Court has ruled -- most recently in 1987 -- that religion-tinged scientific theories have no place in public schools.

A large majority of scientists argue that Darwinian theory is a bedrock without which one cannot understand most of modern science. And they say that new discoveries, from paleontology to the decoding of human DNA, only add more bricks to the Darwinian edifice.

But the Thomas More Law Center, a conservative, religiously grounded nonprofit group that represents the Dover school board, has argued that this case is about freedom of speech. The law center has relied on the work of a small band of scientists and philosophers who take the position that Darwinian theory has gaps and unanswered questions, and that intelligent design is a respectable alternative explanation for the origin of life and the development of new species.

Behe took pains Monday to note that a number of prominent scientists, many of whom are not advocates of intelligent design, have questioned aspects of Darwinian theory. Most criticism concentrates on Darwin's theory of natural selection and variation: Some scientists say that although there is ample evidence of small, evolutionary changes, there is less proof of the grand leaps needed to progress from one-celled life to modern man.

Some scientists argue that life appears to adhere to grand mathematical principles and perhaps inevitably evolves toward complexity and intelligence. "If Darwinian theory is so fruitless at explaining the very foundation of life . . . one can reasonably wonder if there is some other explanation," Behe said.

Behe grounds his argument in his study of biochemical processes. In particular, he focuses on the bacterial flagellum, which is driven by a rotary engine composed of protein and located at an anchor point inside the cell membrane. This powerful organic machine comes equipped with a crankshaft and propeller. Behe argues that this machine is irreducibly complex -- meaning it could not have evolved because it needed all of its parts to work.

Behe's theory is deeply controversial. Earlier in the trial, Darwinian biologist Kenneth R. Miller of Brown University argued that the pieces of the flagellum could function independently and slowly, and over many millions of years evolved to work in concert with other parts.

The question of religion came up several times Monday. Behe freely acknowledged that he is Roman Catholic and believes the hand of the intelligent designer belongs to God. But he emphasized that this was a personal, philosophical belief. Intelligent design, he argued, must succeed or fail as a scientific theory.

More school boards are considering mandating mention of intelligent design. Randy Tomasacci, a school board member from Shickshinny, north of Harrisburg, said his board is debating whether to require teachers to spend a few days on intelligent design. "We're thinking about it," he said. "But we don't want to get sued out of existence."