SCRUPLES, the number-one hardcover and paperback best seller published by Crown and later Warner was Judith Krantz's first novel. I spoke to Judy about the kind of person who writes a pop novel about life, death, love and sex in a Rodeo Drive, Beverly Hills clothing boutique.

"I invariably fall in love with my characters. Billy was going to be a villain; she was going to be so rotten, so arrogant, so spoiled, so rich, such a bitch - and she was going to do something very bad to Spider and Valentine. But early on I realized I'd written myself into a corner. I felt such empathy for Billy as a child, because although I was never overweight I was the most unpopular girl in my school.

"I was a year younger than anybody, I was shorter than anybody, and I was teacher's pet. The other girls loathed me. I was an outcast in this elementary school full of rich kids; my parents were very well-off but my mother despised this rich-kid atmosphere and as a way of combating it, if the other girls had cashmere sweaters, my sister and I didn't. If they had thick socks to go with their loafers, we had thin ones. From the day I started earning money, I started buying myself cashmere sweaters like the other girls". My mother thought her attitude would keep us from being spoiled little Jewish princesses. All it did was make me into a clothes freak.

"I had a theory that, if I could only have a camel's hair coat my life would change. And one day I got a camel's hair coat, but I didn't get any more popular. It was a great shock to learn that it didn't work that way. Then in high school things changed. A whole bunch of new girls came into Birch Wathen and they didn't know I was the least popular girl in the school. And they made friends with me. Being attractive to boys became important. And it happened to me about that time. Suddenly I went from being the outcast to being a member of the "in" group. Then - tragedy. I was skipped again, over my junior year and into my senior year.

"I was now two years younger than any other senior and they didn't want me, in the worst way. And my new friends thought I was being snooty. Then I became editor of the yearbook and editor of the literary magazine and I got the lead in the senior play, and the English teacher was crazy about me and she decided in graduation rehearsal that I would be the first one to walk in. She just said, "Judy walks in first." But that class was rotten to me, they were really rotten to me.

"When I got to Wellesley, it was a totally different story. Nobocy knew my past history; it was like being let loose. I found 400 girls who were prepared to like me. Except for my year in Paris, it was the most exciting, thrilling, happiest time I've ever spent. There was a whole library full of books, boys galore all over the place, and all these wonderful girls from all over the country, most of whom had never seen a Jew before. There was still a quota then. They were fascinated by me. I cried the whole night before graduation because I was convinced that never again would I ever have such a wonderful time. But then, Paris.

"I know it sounds awful to say this, because I've been happily married, 25 years, and I have two sons, but the best year of my life was when I persuaded my parents to leave me in Paris, being 20 and alone and living in a French family and discovering I had a gift for languages."

When I saw her, Judy was about to hit the number-one slot. "Next week number one in The New York Times. Next week number one on the Walden-Dalton list; number one, Chicago Tribune. What I enjoy is beating out The World According to Garp. That book gave me an anxiety attack of monstrous size. I took it away to Aspen on a five-day vacation and I never had a worst time. I thought the first few chapters were marvelous. And I read and read. And then I went "Aaarrrhhhh!" I finished the book like an idiot and it got more and more horrendous and it ruined my vacation. I think Irving's pretentious. Terribly pretentious. But he scared me." [The World, or at least the best-seller list, is still According to Garp in Washington, with Scruples holding at number two.]

Do you feel rivalry, Judy? "No, because the kind of book I write nobody else is doing. It's become, oddly enough, a generic term.There's a new book being advertised as "the Scruples of the Potomac." Reviewers are always saying, "Scruples- type" about other books. But Scruples itself has a lot of fantasy and a lot of humor and I feel it reflects me. So I don't feel rivalry because nobody else can write a book that reflects my own personality. But I certainly feel rivalry when I'm climbing the best-seller list. When I saw Silmarillion was still on that list I called it "silly moron." I could not believe that it had been on the list for a year, people buying it as gifts. There are people with many copies of it and they haven't opened them. I was so anxious to get Silmarillion off the list and for Thorn Birds to go into paperback so I'd have a shot. So yes, I feel competitive rivalry the way a runner does when you see four people ahead of you trying to break the tape. CAPTION: Picture, Judith Krantz, by Charles William Bush