Pat Boone, the all-American boy next door of the '50s, the man in white bucks who pitches milk, religion and conservative politics with equal fervor, has found a touring partner in the same image for the '70s - his daughter Debby, the recording sensation of 1977.

In the age of punk and acid rock, the Beetles, Stones, and Dylan, Debby Boone's recording of "You Light Up My Life" has become the longest running, top-of-the-chart single in the last 23 years. Debby is as much an anomaly in California pop circles as her song. A 21-year-old, church-going, Bible-believing Christian who neither smokes, swears, drinks nor believes in sex before marriage, she is exactly the kind of daughter her father raised her to be. But the slender, blue-eyed Debby, whose clean-cut features greatly resemble Pat's, has become an even bigger success than her father. Her first solo record sold 3.5 million copies, eclipsing even her father's biggest hit, "Love Letters in the Sand."

Released in August, "You Light Up My Life" zoomed to the top of the singles chart faster than any other record last year (seven weeks) and stayed there longer (13 straight weeks on the Billboard chart). Not since Kitty Kallen recorded "Little Things Mean a Lot" in 1954 has a recording by a female vocalist topped the charts for so many weeks. Her debut performance won her four Grammy nominations this week: best new song, best new artist and best pop vocal performance.

The third of four daughters born to Boone and his wife, Shirley, the daughter of the late Country-Western Red Foley, Debby was the most rebellious of the girls. The four sisters (the others are Cherry, Lindy and Laury are 3 1/2 years apart. They were all dressed alike as children and taught by their mother to sing in four-part harmony. The Boone family had an image, they sang together, they prayed together. They were a model family. After all, father Pat Boone was the author of "Twixt Twelve and Twenty," a book that gave advice to teenagers.

When Debby was 12, Pat told his daughter that if they could work up one song for his act they could accompany him on a tour of Japan. The girls came up with "What the World Need Now Is Love." But Pat, who was ager to keep his family together, was impressed enough to take them with him to the Orient. With Debby as the lead singer, the Boone Sisters Qualiet followed their father on the summer-music circuit of state fairs and amusement parks. "It was one way of keeping four pretty teenage girl in view at the same time," their father says today.

During adolescence, however, Debby began to rebel against her parent's strict discipline, their dress and clothing regulations, early curfews, and prohibition against dating until she was 16 "Peer pressure was very strong," she says," "and I began to feel really alienated from my parents. I thought what they were doing to me wasn't fair."

Debby began to dress sloppily, to smoke secretly (although she was frequently caught) to listen to acid rock (even though she didn't like it) and to hang black-power posters and pictures on riots in her room. "That was my statement," she says. "My dad just hate it all. He couldn't understand why I couldn't be like my sisters with flowers and stuffed animals and things."

Despite her rebellion.her parents maintained enough authority to keep her from wandering too far away. "There were still some things I couldn't do no matter how much I wanted to," she remembers. "Suddenly I found myself alone, an individual, but an unhappy one. So I began to question which side did I really want to be on."

The critical point in her rebellion came on her second trip to the Orient. One night, after her parents had gone out, she went to their room to retrieve some cigarettes in an ash tray. "They were already half smoked." she recalls, "but I figured better than nothing. so I smoked three of them and threw the butts out the window and went back to my room feeling like I'd really put one over.

"For some reason my dad remembered the cigarettes and he came directly into my room, woke me up and said, 'All right, where are they?" I was just appalled. How could he accuse me? I mean there were three other girls there. Finally, I admitted it, but I was enraged and offended. I forget what the punishment was but when he left the room I was hysterical, so I went into my older sister's room to tell her how much I hated him."

Her older sister, instead of offering sympathy, cried and recounted a story her mother had told her the night before. "My dad was talking to my mother and worrying what to do about me. It seemed like every time he tried to get close, he always did the wrong thing. Suddenly he started to cry, and he got down on his knees and started to pray for me.

"I didn't want to be affected by it," she says candidly, "but I was, also because my sister was crying and upset by it too. I couldn't shut it out of my mind because it was a rare expression of love."

Reflecting about that time of his life, Pat Boone says, "I felt more of a failure during that period than I ever have as an entertainer or a person. Suddenly everything you do seems wrong. Everything you say gets misunderstood. I had a lot to learn about what a good father does."

Pat's prayers broke Debby's rebellion, and although periods of intense questioning followed, she gradually embraced the family's conservative and religious lifestyle. After graduating from high school, she worked with emotionally disturbed children for a year as a volunteer, then attended Bible school for a year and a half. Still, she had her heart set on singing.

Record producer Mike Curb, the man who has produced the Boone family's records since 1975, searched two years for an appropriate single to introduce Debby as a solo entertainer. Curb, a Ronald Reagan protege who plans to run for lieutenant governor in California this year, found that song at a special screening of "You Light Up My Life," a film about a young girl trying to break into the music business. The title song, composed by writer-director-producer Joe Brooks, is a hearttugging, middle-of-the-road ballad, as sugary as Pepsi-Cola, a product for which Brooks also composed the jingle, "You've got a lot to live/and Pepsi's got a lot to give."

In the movie the title song is sung by Kasey Cisyk an obscure jingle singer whose voice sounds much like Debby's.(Cisyk dubbed the song for actress Didi Conn.) Curb promptly arranged with Brooks to borrow the instrumental track, flew Debby to New York, and cut the record, returning Kasey Cisyk to obscurity. Life imitating art, the song shot to the top of the charts, just as the heroine's song did in the movie.

While the heroine was presumably thinking about a man, Debby was thinking about God when she recorded her version. "That's one of the things that's made the song such a phenomenal success," she says. "The lyric lends itself to almost any kind of love relationship, not just a romantic girl and guy thing. I run into people all the time who associated it with a spiritual relationship as I did."

Pat is understandably proud of his daughter. "Debby knocks me out," he says. "Not only does she sing better than I think I ever have, but she's able to handle the rush of success with such poise and perspective that it absolutely amazes me."

Boone, who never intended any of his girls to end up in show business, hopes that Debby's career is shortlived. "I hope by the time she's 25, she's found the right guy and has had enough fun and pressure that she'll realize she wants more to life than the next hit record or TV special. I hope being a wife and mother ultimately will be more fulfilling for her."

If it comes to a choice between career and marriage, Debby says she'll willingly give up her career, but doesn't think it will come down to that. There is no man who currently lights up her life. "Some of my best friends are guys," she says, "but I have no real romantic interest right now."

Perhaps the man she is still closest to is her father. Both say that their stormy battles during Debby's teens have made them even closer now. For Debby the turning point was in Japan; for Pat it was in Columbus, Ohio, two years ago when the family appeared at the state fair. They all thought it was going to be their last show together.

"We all were in an emotional state," he recalls. "Debby (who was 19 then) had left the room to go and get candy; and was gone for a half-hour. I was worried about her and went to find her. She was in the lobby talking to some musicians, but was upset that I embarrassed her in front of them. It was a trivial matter really, but when we got back to the room I thought she was pretty sassy. One thing led to another and suddenly I threw her over on the bed and spanked her in front of her monther and her sisters."

Afterwards, feeling chagrined and guilty, the father apologized to his family and led them all in prayer. "But there were no hugs and kisses that night," he remembers.The next day on the plane, he heard Debby laughingly tell the girls about the black and blue marks on her battom. "I found there were tears in my eyes," he says, "for I realize Debby had let me off the hook. Overnight, she had forgiven me for being out of line."

Still friends, Pat and Debby left Lost Angeles yesterday morning for a performing tour of South Africa.

If Debby's identity seems very much like her father's it is not by choice.

"People seem to feel that I'm not enjoying life to the fullest," she says in the family room of the Beverly Hills home where she still lives with her parents. "They think I'm squelching what I really want to be or the true at all. This isn't something forced on me. It's a way of life I've chosen for myself, and I'm very happy with it," she flashes an engaging smile.