Republican U.S. Sen. Elizabeth Dole, who speaks often about prayer and faith, is gambling her re-election bid by raising religion in the campaign's final days.

In a television ad this week, Dole questioned the Christian credentials of Democratic challenger Kay Hagan. The state senator responded angrily, filing a lawsuit on Thursday and airing an ad of her own that says Dole is breaking the Bible's Ninth Commandment by bearing false witness.

The two candidates are locked in one of the nation's closest Senate races. An Associated Press-GfK poll released this week found Hagan has a slight edge. The pair has spent months swapping negative ads, but even some Republicans think Dole's assertions about Hagan and her faith have gone too far.

"It's pretty risky," said Republican political consultant Carter Wrenn, who worked for the late Jesse Helms, the senator Dole replaced in Washington six years ago. "Anytime you start questioning somebody's religion, you're getting on thin ice."

Dole was once considered such a sure thing that Democrats struggled to recruit a challenger for a Senate seat that has been in Republican hands for 35 years. But a surge in Democratic registrations and excitement surrounding the party's presidential nominee Barack Obama have boosted Hagan's campaign.

Dole's 30-second advertisement shows clips of some members of an atheist advocacy group — the Godless Americans Political Action Committee — talking about some of their goals, such as taking "under God" out of the Pledge of Allegiance and removing "In God We Trust" from U.S. currency. It goes on to question why Hagan went to a fundraiser at the home of a man who serves as an adviser to the group.

"Godless Americans and Kay Hagan. She hid from cameras. Took Godless money. What did Hagan promise in return?" the narrator says.

The ad ends with a picture of Hagan while another woman declares in the background, "There is no God!"

Hagan is a Presbyterian church elder who teaches Sunday school. On Wednesday, her attorneys demanded the ad come down within 24 hours. On Thursday, Hagan's attorneys filed a lawsuit in Wake County Superior Court accusing Dole of defamation and libel.

"Each airing of the advertisement further injures (Hagan's) good name and reputation in the community," Hagan's attorneys wrote in court documents. Thursday's court filing does not detail Hagan's full case against Dole, but allows Hagan 20 days to file the full complaint.

Dole's campaign says the ad does not question Hagan's faith, only her agenda and associations, and attorneys for Dole said in a letter to Hagan's legal team that the ad was factual. Dan McLagan, a Dole spokesman, said the campaign had no plans to pull the ad from the air and dismissed the lawsuit as a "silly political gimmick."

"This lawsuit is frivolous and we will file a motion to dismiss," he said. "Kay Hagan knows that the Dole campaign ad is accurate and she is trying to confuse voters until Election Day."

Hagan responded Thursday with an 30-second spot of her own. Referring to the Ninth Commandment in the Old Testament, Hagan says the campaign is about creating jobs and fixing the economy, "not bearing false witness against fellow Christians."

"Elizabeth Dole's attacks on my Christian faith are offensive," Hagan says in the ad. "She even faked my voice in her TV ad to make you think I don't believe in God. Well, I believe in God. I taught Sunday School. My faith guides my life, and Sen. Dole knows it."

The editorial board of The Charlotte Observer, the state's largest newspaper, compared Dole's ad to an infamous spot run in 1990 by Helms against challenger Harvey Gantt, who is black. That ad showed a pair of white hands crumpling a rejection letter, while a narrator slammed "racial quotas."

Wrenn, who helped write the so-called "hands" ad, said both ads were probably put together under similar circumstances.

"When you get down into the 11th hour of a campaign, the pressure gets up pretty high, and your sleep deprivation factor gets up pretty high," Wrenn said. "Sometimes you just lose your judgment a little bit."