Former Pennsylvania Senator Rick Santorum publicly thanked an atheist group this week for making him a poster boy in their latest "Go Godless" campaign.

American Atheists posted a set of highway billboards in Texas on Monday to advertise a forthcoming convention in Austin to celebrate its 50 anniversary.

"Our civil laws have to comport with a higher law. God's law." the billboard quotes Santorum. The quote, from a speech Santorum delivered in Iowa as a presidential candidate, is underscored with the slogan, "Go Godless instead."

On Tuesday, Santorum shot back at the atheists in an e-mail to his followers.

"I know, it is shocking," the one-time Inquirer columnist wrote.

"And you know what I said back to the American Atheists who purchased that billboard? Thank you. Thank you for helping me publicly express my strong belief that we need to continue to be one nation under God. And I think you would agree with that statement."

A spokesman for the American Atheists, based in Cranford, New Jersey, said he was disappointed at Santorum's reaction.

"In this country we have separation of church and state for very good reasons, said Dave Muscato. "We are not 'one nation under god,' but 'one nation indivisible'."

Santorum is one of three Republicans the American Atheists are "shaming" in Texas. Sarah Palin and Newt Gingrich are also singled out. Also targeted are Pope Benedict XVI and the Rev. Robert Jeffress, pastor at the First Baptist of Dallas.

Palin is (mis)quoted as saying "We should create law based on the God of the Bible;" Gingrich is quoted as saying with "How can I trust you with power if you don't pray;" the Pope Emeritus is pictured with a New York Times headline that reads "The Church Protected Priests Who Abused Children;" and Jeffress quoted with "What they (homosexuals) do is filthy."

Santorum claimed the billboards prove that religion is under attack in the United States.

"This is also a reminder that there are strong forces against the fundamental beliefs that you and I hold so dear," he wrote. "They are organizing with determination to transform the very fabric of our country. The stakes are simply too high for us to sit back and ignore the progress they are making."

Muscato said that wasn't why American Atheists bought the billboards.

"The intent was to draw attention to ridiculous things that our politicians are saying and get people to stand up and take notice," he said.

Contact staff writer Sam Wood at 215-854-2796 or samwood@phillynews.com.