Imagine their surprise, those natives lurking in the doorways of Times Square, where the gamut of architecture runs from porn to pawn, dusk to dawn, every kind of sleaze, tease and please imaginable . . . the neon-eyed guys leaning against the windows like hit men from Venus, the girls, the boys, the boy-girls, the girl-boys . . . imagine their shock when they saw a president of the United States under a marquee advertising "Best Porn in Town!" and a movie with the mysterious title, "DIRTY RADIO SEX."

And then the president, in baseball hat and T-shirt, began to sing.

He began to sing a hymn on the same day his former vice president, Walter Mondale, was decrying the threat of church and state getting too close. Here was Jimmy Carter leading his wife Rosalynn and 40 church volunteers in a rendition of "This Is the Day the Lord Hath Made."

Actually, the way the former president put it, the visit to the pornucopia of Times Square Thursday would seem to have had nothing to do with smut, lust in the heart or another attraction the marquee described as "SEx GODDESS For Adults OnlyXXX$1.99."

They were looking for the subway, Carter said. Really.

"It's a curiosity. Most of the people in our party have never taken the subway and they wanted to see what it's like," he explained.

Carter and other volunteers have been staying at the Metro Baptist Church on West 40th Street. They've been in New York this week to help renovate a burned-out six-story building on Manhattan's East Side. They are working for Habitat for Humanity, a nonprofit international Christian organization that helps the homeless and the destitute.

"Make sure you get the marquee," Carter said to a photographer and stopped to offer photo opportunities in front of an XXX establishment.

Then Carter led the 40 the rest of their two-block way to Sixth Avenue, where they disappeared into the subway. Later, it was reported, they surfaced to eat at Katz's deli.