NEW YORK -- The commercials in question use an ancient advertising device -- testimonials from satisfied customers.

There's the gray-haired man in the muffler talking about how lonely Christmas used to be. "Coming back changed all that," he says, now surrounded by carolers.

There's the thirtyish woman talking about her confusion after the divorce. "Thank God I had enough sense to come home," she smiles.

"It's good to be back," says another cheery soul. It's a touch reminiscent of an old Brylcreem ad ("I came back!" "I came back!") until the closing shot -- the former stray walking into the open doors of St. Raymond's Church in the Bronx -- and the voice-over, "Come home at Christmas time."

This 30-second commercial, which is airing an average three times a week on four New York TV stations, has been a friendly elbow in the ribs from the Catholic Archdiocese of New York and those ubiquitous ad folks from Batten, Barton, Durstine & Osborn Inc. -- better known as BBD&O, pushers of Pepsi, Dodge, Armstrong Floors and Wisk.

Adding in the spots on nine radio stations, the transit cards on 4,700 subway cars and 1,500 buses, and the Spectacolor ad on the electronic billboard in Times Square, the archdiocese will spend something like $400,000 (it declines to provide figures) to try to lure inactive Catholics back to church this Christmastide. That may amount to the most expensive religious ad campaign underway this season, but it's hardly the only one.

Increasingly, religious groups are betting that the same techniques that can move mouthwash and encourage seat belt use can help recruit priests, urge Sabbath observance, turn lapsed believers back into active worshipers. In print and on the airwaves, everyone from real-life archbishops to Father Guido Sarducci -- the "Saturday Night Live" pseudopriest -- seems to have a message from the Ultimate Sponsor.

"Jesus and the Apostles went to the marketplace," reasons Eileen Marx, communications director of the Archdiocese of Washington, which has bought radio spots on three stations for its Christmas messages. "Today's marketplace is the media."

The pace picks up at this time of year, of course. "We believe that psychologically it's a very good time ... a time when we can appeal to the heart as well as the head," says the Rev. Alvin Illig of the Paulist National Catholic Evangelization Center in Washington. He estimates that more than 25 Catholic dioceses mount "Come Home for Christmas" campaigns, ranging from New York's high-profile effort to a more modest New Orleans TV spot starring a robed Archbishop Philip Hannan "in a very straight, on-camera pitch, wishing everyone the joys of the season and reminding them there's no better time to visit their churches," says an archdiocesan spokesman.

Most of these outreach campaigns are aimed not at creating converts but at reclaiming the fallen-away -- who, according to Gallup organization figures, account for more than a quarter of all baptized U.S. Catholics.

At Christmas time, "inactive Catholics feel a little bad," notes Father Illig. "A little guilty." Some notable ad campaigns have tried to tap that guilt.

One of last year's BBD&O-produced spots for the Archdiocese of New York, for instance, showed a father and son trimming a Christmas tree, the little boy remarking on each ornament he lifts from the box. Junior does fine with Santa and reindeer, but when he picks up a cre`che he wonders, "What's this, Daddy?" Dad looks troubled; as the ad's copywriter puts it, he's thinking, "My God, he recognizes Rudolph and Frosty the Snowman and has no idea who Jesus is." Cut to shot of family walking hand-in-hand up the steps of St. Patrick's Cathedral.

Catholics are not the only religious group to try outreach through advertising. The Brooklyn-based Lubavitch movement, the most enterprising of the Hasidic groups in trying to reach inactive Jews, maintains a virtual publicity armamentarium: billboards and subway posters, radio spots, a fleet of Mitzvah-Mobiles (minitrucks that traverse New York offering onsite prayer and literature), national cablecasts and full-page ads in The New York Times ("Lighting Shabbos candles can affect your entire life ... Return this coupon today and we'll gladly send you a free instruction booklet ...").

Unchurched Protestants, for their part, are being wooed through a slickly ironic campaign by the Episcopal Ad Project. Perhaps as many as 3,000 churches of various denominations around the country have purchased the Project's print ads, at a bargain 10 bucks per, and bought space in local newspapers to run them. "They invite people to give religion a try again," explains Dean Hanson, art director at Fallon McElligott, the Minneapolis agency that created the ads. "It's like, 'Have you driven a Ford lately?' "

Launched 11 years ago at the behest of the Rev. George Martin, then pastor of a dying downtown congregation, the Ad Project uses striking -- and cheap -- images, often from ecclesiastical art. "If we use a painting of the Last Supper, we don't have to pay Leonardo anything," reasons Hanson.

The Ad Project also makes use of that particularly tricky advertising gimmick, humor. One of its ads, for instance, promised that the Episcopal Church would welcome worshipers "regardless of race, creed, color or the number of times you've been born." It's taken some flak for its irreverence and for its anti-Moral Majority politics.

The criticism demonstrates the potential mine field that ad makers walk through when the product they're packaging is a spiritual one. "Some people take religion so seriously they can't ever laugh at it," Father Martin acknowledges.

A small Catholic order, the Missionary Oblates of Mary Immaculate, learned about such sensibilities last year when the Rev. Alan Maes turned to magazine ads to recruit candidates for the priesthood. Wondering how to reach young men ("I thought we had to do something outrageous"), he hit on the notion of an endorsement from comedian Don Novello, a k a Father Guido Sarducci.

The ad, written by moonlighting Chicago ad professionals, ran in Newsweek on Campus and Student Life, featuring a robed Father Guido twirling spaghetti on a fork with the headline, "Eat Free at Italian Restaurants." The copy captured Novello's not-entirely-elevated style ("You think they're gonna let the check slide if you're a doctor or lawyer? Don't hold your breath") and noted such "padre perks" as helping one's fellow man and getting first crack at parish rummage sales.

Some Catholic leaders, including an Indiana bishop who denounced the ad in a diocesan newsletter, were not amused. "It was in terrible taste, most of us felt," says the Paulist Center's Father Illig. Father Maes remains entirely unrepentant.

But even sober religious advertising causes some uneasiness. Aren't priests supposed to be called by God, not Newsweek? Is advertising appropriate at all?

And is it what religious organizations should be doing with their money? Effective advertising can be expensive, even when agencies donate their creative talents (as BBDO, Fallon McElligott and Don Novello and friends all did), production houses agree to lower their prices and media outlets offer reduced ad rates. The Lubavitchers spend hundreds of thousands of dollars annually (but less than a million, a spokesman says) on their public relations and advertising apparatus. That single page in Newsweek on Campus cost the Missionary Oblates $12,000.

Some religious organizations historically have gotten past the money problem by prevailing on TV and radio stations and newspapers to run their messages as PSAs -- public service announcements. The Mormons' extensive "Home Front" campaign, now in its 17th year of promoting "family solidarity," relies entirely on receiving an estimated $5 million to $10 million worth of free time and space.

But broadcasters are growing less willing to air PSAs, according to Lois Anderson, director of communications for the interdenominational Religion in American Life, which also relies on donated time. "With deregulation, stations don't have to do this," Anderson says. A free spot may air at 2 a.m. And the more specifically sectarian the message, the less likely it is to secure free newspaper space or air time, as the Mormons discovered when they produced a "Christ-centered" PSA one Christmas.

Moreover, running ads for religion is itself something of an act of faith. Lever Brothers has sales records to tell it whether its ring-around-the-collar ads sold more Wisk; just how many Catholics BBD&O's current campaign for the Archdiocese of New York will bring home for Christmas will probably never be determined. Such market research would cost more than the ads themselves. "We can't count this Sunday and next Sunday and the next and say, 'We're up 13.2 percent and showing strong market support,' " says Joe Zwilling, the archdiocese's assistant communications director.

Father Martin's aging parish, St. Luke's Episcopal Church in Minneapolis, saw the average age of its parishioners drop from 55 to 40 over five years, and its Sunday school grow from 15 children to 100 over 11 years; he credits the Episcopal Ad Project with the resurgence. But if ads can draw parishioners, they can't necessarily keep them. "We have a franchise operation, when you think about it, and we don't control the franchisees," he notes. "We don't know if the churches buying the ads are truly welcoming, if they're offering 'quality worship.' "

Despite the uncertainties, religious groups continue to cast considerable bread upon the waters.

The Archdiocese of Detroit would have paid about $1.5 million at standard commercial rates for its recent media blitz to attract potential priests to Sacred Heart Seminary. N.W. Ayer's Detroit office, whose major secular client is General Motors, volunteered to conceive and produce print ads, billboards, radio and television spots around the theme "The work is hard. But the rewards are infinite."

The priests in the ads are purposeful and somewhat glamorous. The television spot, for instance, shows a square-jawed cleric in a trench coat striding down a hospital corridor toward a little girl brought in by ambulance. (Ayer's creative supervisor Tom Wehner had initially planned to place the priest-hero in a prison; the archdiocese thought that was "a little negative.") "I just hope I can make a difference here," thinks the stalwart priest, as if he were more in the business of saving lives than souls. "But then again, I'm not alone in this."

In part, this is good old Madison Avenue accentuate-the-positivism. "You don't advertise 'Come be a priest and be celibate and live on $160 a week and spend your life working with the hopeless and the dying,' " Wehner points out.

But the emphasis on the priesthood as a high-intensity job had another subtext. "We thought one of the deterrents to becoming a priest is a perception among young men that normal people don't do it ... We chose to make the life of a priest a normal thing, {to use} the language of career rather than the language of piety or spirituality." Ayer used a dollop of humor, too; one print ad declared, "We want to collar a few good men."

How many future priests the campaign will collar is unmeasurable, but inquiries at Sacred Heart Seminary have at least doubled since last spring, according to the Rev. John West, associate vocations director. (The pope's summer swing through Detroit may also have helped.) "People all over can quote our lines verbatim," Father West boasts.

N.W. Ayer believes this to be the first use of television to recruit priests, but it may not be the last. Ayer and the archdiocese plan to make the ads available to other dioceses; BBD&O and the Archdiocese of New York are pondering a similar "syndication" of their "Come Home for Christmas" campaign.

The creative possibilities are only beginning to be tapped. Coming soon, perhaps: testimonials from celebrity faithfinders like Charles Colson? Campaigns for individual sacraments? The first hummable jingles? "It would be very expected to show someone burning in Hell and say, 'If you don't want this, you'd better go to church,' " says Dean Hanson of Fallon McElligott. "You have to do something that's unexpected."