"We took the boys to see the movie of 'Kramer vs. Kramer,' and it was mind-boggling. I couldn't talk. I tried to ask Nickie what he thought of it, but I literally couldn't get the words out. Because he and his brother -- they were what it was about."

Avery Corman is not divorced. He and his wife, Judy have been married 12 years, and their kids are now 8 and 5, and he is delighted when somebody thinks his book, "Kramer vs. Kramer," is about his own life.

"It's very flattering," he says. "It means I've been able to communicate what I felt."

What he felt was very simple: the silent, proud, fierce and achingly shy love of a father for his child.

"That was my starting point, what it was like being a daddy. Then I developed it: What if something happened, if the family broke up . . . .?"

In the story, Joanna Kramer takes off, feeling smothered by the roles she is being forced into. More than a year later, having created her new self, she returns to claim her 4-year-old son, Billy. But Billy and his father Ted have formed a bond, so the case goes to court. Joanna wins custody, but that is not the end.

Corman loves the film, which brings the already concise novel into tighter focus by selecting out scenes and characters and sharpening the dialogue a bit. It also gives Joanna a $31,000 job, better paid than Ted's while the book had her "sort of a girl Friday" for a racquet club.

"You could teach a film course with that movie. I think one reason it worked so well," Corman remarked during a visit to town yesterday, "was that Bob Benton is a daddy. Stanley is a daddy. Dustin is a daddy."

Benton, who directed and wrote the screenplay, and producer Stanley Jaffe and the male lead, Dustin Hoffman, did somehow get across the same sense of "being connected to the material," as the author put it. And Meryl Streep, as Joanna, managed to go beyond the book a little in subtly suggesting that one day, one way or another, the Kramers might get together again.

Things are looking good for Avery Corman right now. Just as his best seller began to fade, he sold the paperback rights for $625,000 and the screen rights for $200,000, which means he can work on his new novel in relative peace.

It wasn't always that way. At 44, a free-lance writer since his 20s, he is no instant sensation. Like Ted Kramer, he started as an ad salesman after NYU.But he soon realized it was not for him, began writing plays, had a couple of near misses and decided Broadway was just too nerve-wracking. So he wrote a novel. He did it without an advance, sold it to the first publisher. The book was "Oh God!" and the year was 1971.

"It wasn't till six years later that they made the movie of it. I was halfway through 'Kramer' when I heard. People ask me if I write for the movies, but I don't think of myself that way at all. All I'm thinking about is gettiing to the end of the book."

"Oh God!" didn't bring in enough to live on, so Corman wrote articles and some documentary films for high schools. His wife was a rock music publicist at the time.

"I knew I was buying time with these jobs," he said, "but it was important to me that they were good jobs, good enough to make me feel proud of my work even though my heart was elsewhere."

Now he is free to concentrate on his next book, a serio-comic look at the way things were for New Yorkers from the '50s on. He works slowly, stopping to get the right word, paring, condensing.

He hopes 'Kramer vs. Kramer" will bring out the father-love in more men,, will help them to cherish the too-soon-gone years when their children are small and not put off real life in favor of careers and other games.