HARRISBURG -- A leading proponent of "intelligent design" acknowledged yesterday in a trial over its place in public schools that major scientific organizations and even his own colleagues oppose his ideas, but he said their criticisms aren't scientifically based.

"Not every statement issued by a scientific organization, even on science, is a scientific statement," Lehigh University biochemistry professor Michael Behe said.

Dr. Behe testified for a second day as the first witness called by a school board that is requiring high-school biology students to hear a statement about the concept of intelligent design. The landmark federal trial could decide whether the concept can be mentioned in public school science classes as an alternative to the theory of evolution.

Dr. Behe, who was expected to resume testifying today, contends 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 Dr. Behe, a Roman Catholic, has testified that he personally believes it to be God.

During cross-examination of Dr. Behe, Eric Rothschild, a lawyer for eight families suing to have intelligent design removed from the Dover Area School District's curriculum, cited a resolution from the American Association for the Advancement of Science as an example of opposition from mainstream scientists.

The resolution passed by the association's board in 2002 urges "citizens across the nation" to oppose policies that would allow the teaching of intelligent design as science in public schools.

"This is a political document," Dr. Behe said. "What scientific paper do you know where it says, 'whereas'?"

Similarly, Dr. Behe said Lehigh's biology department cited no scientific evidence in a statement posted on its Web site in August that says intelligent design "has no basis in science."

"It doesn't carry the weight of a single [scientific] journal paper," 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 about the concept.

The families argue that the policy essentially promotes the Bible's view of creation, and therefore violates the constitutional separation of church and state.

The trial began Sept. 26.

The plaintiffs are represented by a team put together by the American Civil Liberties Union and Americans United for Separation of Church and State. The school district is being represented by the Thomas More Law Center, a public-interest law firm that says its mission is to defend the religious freedom of Christians.