For several months, a 20-by-60-foot billboard on busy northbound I-95 in Philadelphia had proclaimed: "Don't believe in God? You're not alone."

Now, the billboard has a looming picture of the Blessed Virgin and says, "Say One Hail Mary."

The first billboard gave a Web site: www.phillyCOR.org, the Philadelphia Coalition of Reason, a consortium of atheists, agnostics, skeptics, rationalists and religious free-thinkers.

The new one just says: "Brought to you by God, the Father." No Web site is listed.

It took a flurry of inquisitive calls yesterday to discover who had paid for the message.

"We didn't pay for it," said Donna Farrell, communications director for the Roman Catholic Archdiocese of Philadelphia, "and we don't know who did."

The sign is the work of a group known as Holy Souls Ministries, according to Stephen Gorlechen, executive vice president of Steen Outdoor Advertising, of Philadelphia. He said a man named Joe Veltri made the arrangements.

Veltri did not return several phone messages.

Terry Steen, president of the ad company, describes himself as a "deeply religious person" who believes in "freedom of religion." So his firm leased the space to express opposing points of view.

Steve Rade, 70, the Huntingdon Valley business executive who paid $22,500 for the atheist/agnostic billboard, said someone "is trying to erase our message" by renting the billboard when his time on it was up. "They're too late. The response was excellent. We're going to roll out a nationwide program."