Updated

Sen. Rick Santorum says he intends to withdraw his affiliation with the Christian-rights law center that defended a school district's policy mandating the teaching of "intelligent design."

Santorum, the Senate's No. 3 Republican who is facing a tough re-election challenge next year, earlier praised the Dover Area School District for "attempting to teach the controversy of evolution."

But the day after a federal judge ruled the district's policy on intelligent design unconstitutional, Santorum told The Philadelphia Inquirer he was troubled by testimony indicating religion motivated some board members to adopt the policy.

Santorum was on the advisory board of the Michigan-based Thomas More Law Center, which defended the district's policy. The law center describes its mission as defending the religious freedom of Christians.

"I thought the Thomas More Law Center made a huge mistake in taking this case and in pushing this case to the extent they did," Santorum said Wednesday. He said he would end his affiliation with the center.

The leading Democratic challenger in Santorum's 2006 re-election battle, state Treasurer Robert P. Casey Jr., accused him of backtracking on intelligent design.

Casey spokesman Larry Smar said Wednesday that Santorum's statements were "yet another example of 'Election Year Rick' changing his positions for political expediency." Casey has led Santorum in recent polls.

U.S. District Judge John E. Jones ruled Tuesday that the Dover district's policy of requiring students to hear a statement in biology class about intelligent design was "a pretext ... to promote religion in the public school classroom." The statement said Darwin's theory is "not a fact" and has inexplicable "gaps." It referred students to an intelligent-design textbook

Intelligent design's proponents hold that living organisms are so complex they must have been created by a higher force rather than evolving from more primitive forms. Critics, including those who challenged the school district, say it amounts to a secular repackaging of creationism, which the courts have already ruled cannot be taught in public schools.

Santorum said in a 2002 Washington Times op-ed article that intelligent design "is a legitimate scientific theory that should be taught in science classes."

But he said he meant that teachers should have freedom to mention intelligent design as part of the evolution debate — not be required to do so — and said his position hasn't changed.

Santorum said he disagreed with the Dover board's policy of mandating the teaching of intelligent design, rather than teaching the controversy surrounding evolution. Because of that, he said the case provided "a bad set of facts" to test whether theories other than evolution should be taught in science class.