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The Rev. Billy Graham urged North Carolina voters Wednesday to support an amendment to the state constitution banning gay marriage, a move that an observer said was highly unusual but another said was in keeping with the minister's moral beliefs.

"Watching the moral decline of our country causes me great concern," said Graham, 93, who lives near Asheville. "I believe the home and marriage is the foundation of our society and must be protected."

His complete statement about Amendment One will be part of full-page ads slated to appear in 14 North Carolina newspapers throughout the weekend.

Graham's statement was issued by the Charlotte-based Billy Graham Evangelistic Association, which is led by Graham's son, the Rev. Franklin Graham. Franklin Graham recorded a message last month in support of Amendment One, which is on the ballot in the election Tuesday.

"At 93, I never thought we would have to debate the definition of marriage," Billy Graham's statement said. "The Bible is clear — God's definition of marriage is between a man and a woman. I want to urge my fellow North Carolinians to vote for the marriage amendment" Tuesday.

William Martin, who wrote the authorized Graham biography "A Prophet With Honor," couldn't recall another effort by the Billy Graham Evangelistic Association like the one the ministry plans in support of Amendment One.

The elderly evangelist preached often on the need for sexual purity, but rarely spoke about same-sex marriage, Martin said.

"I am somewhat surprised that he would take that strong a stand," said Martin, professor emeritus of religion and public policy at Rice University. "In the past, I have heard him say with respect to homosexuality, there are greater sins. Franklin has been more outspoken about it, but it sounds as if this is Mr. Graham expressing his own will."

Although Graham's last crusade was in 2005, he remains deeply influential. In April 2010, President Barack Obama made the pilgrimage to meet with Graham, continuing a tradition of counseling commanders in chief that began with Dwight Eisenhower.

Since the death of his wife, Ruth Bell Graham, nearly five years ago, he has spent most of his time at his home in Montreat. Public appearances have been rare, and he's been hospitalized several times, most recently in December for pneumonia.

Danny Akin, president of the Southeastern Baptist Theological Seminary in Wake Forest, said he's not surprised that Graham took such a strong stand on Amendment One.

"I think he would see this as I do, not so much as a political issue — which it is — but a moral issue," Akin said. "He believes it's right to affirm that marriage should be understood as a covenant between a man and a woman."

Billy Graham's daughter, Anne Graham Lotz, also has said she supports the amendment.

North Carolina already outlaws gay marriage, but adding that ban to the state constitution would make it much harder to change in the future. Opponents to the amendment argue the language is vague and it could have wider consequences beyond those for gay couples.

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AP Religion Writer Rachel Zoll contributed to this report from New York.

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Martha Waggoner can be reached at: http://twitter.com/mjwaggonernc