WILMINGTON, Del. — Republican Senate nominee Christine O'Donnell of Delaware on Tuesday questioned whether the U.S. Constitution calls for a separation of church and state, appearing to disagree or not know that the First Amendment bars the government from establishing religion.

The exchange came in a debate before an audience of legal scholars and law students at Widener University Law School, as O'Donnell criticized Democratic nominee Chris Coons' position that teaching creationism in public school would violate the First Amendment by promoting religious doctrine.

Coons said private and parochial schools are free to teach creationism but that "religious doctrine doesn't belong in our public schools."

"Where in the Constitution is the separation of church and state?" O'Donnell asked him.

When Coons responded that the First Amendment bars Congress from making laws respecting the establishment of religion, O'Donnell asked: "You're telling me that's in the First Amendment?"

Her comments, in a debate aired on radio station WDEL, generated a buzz in the audience.

"You actually audibly heard the crowd gasp," Widener University political scientist Wesley Leckrone said after the debate, adding that it raised questions about O'Donnell's grasp of the Constitution.

Erin Daly, a Widener professor who specializes in constitutional law, said that while there are questions about what counts as government promotion of religion, there is little debate over whether the First Amendment prohibits the federal government from making laws establishing religion.

"She seemed genuinely surprised that the principle of separation of church and state derives from the First Amendment, and I think to many of us in the law school that was a surprise," Daly said. "It's one thing to not know the 17th Amendment or some of the others, but most Americans do know the basics of the First Amendment."

O'Donnell didn't respond to reporters who asked her to clarify her views after the debate.

During the exchange, she said Coons' views on creationism showed that he believes in big-government mandates.

"Talk about imposing your beliefs on the local schools," she said. "You've just proved how little you know not just about constitutional law but about the theory of evolution."

Coons said her comments show a "fundamental misunderstanding" of the Constitution.

The debate, their third in the past week, was more testy than earlier ones.

O'Donnell began by defending herself for not being able to name a recent Supreme Court decision with which she disagrees at a debate last week. She said she was stumped because she largely agrees with the court's recent decisions under conservative chief justices John Roberts and William Rehnquist.

"I would say this court is on the right track," she said.

The two candidates repeatedly talked over each other, with O'Donnell accusing Coons of caving at one point when he asked the moderator to move on to a new question after a lengthy argument.

"I guess he can't handle it," she said.

O'Donnell, a tea party favorite who stunned the state by winning the GOP primary last month in her third Senate bid in five years, called Coons a liberal "addicted to a culture of waste, fraud and abuse."

Coons, who has held a double-digit lead in recent polls, urged voters to support him as the candidate of substance, with a track record over six years as executive of the state's most populous county. He said O'Donnell's only experience is in "sharpening the partisan divide but not at bridging it."