Ellyn Satter, you might say, is a born-again diet counselor.

For years she counseled and helped her clients to lose weight and then watched them gain it all back. She used all the latest weight-control techniques and watched them all raise and dash hopes in direct correlation to pounds lost and regained.

Then she began seeing eating disorders and, little by little, keeping a sharp eye on the research and experience of the experts, she tracked the problem back to what she sees as "eating-disordered families."

Out of all this came a book she describes as "a revolution in lamb's clothing," a primer for child-feeding that is, in truth, a metaphor for child-rearing.

The book, "Child of Mine, Feeding with Love and Good Sense" ($9.95, Bull Publishing Co., 422 pp.) is an excellent source of solid nutritional information. In addition, it espouses a philosophy of moderation and common sense that fosters good health, good eating habits and, most of all, a loving relationship between parents and children.

Obesity is not dismissed as a problem, but Satter believes that there is only so much that parents can do to prevent it.

"I know this seemed pretty dangerous when I first put it down on paper," she says, "but in spite of the best efforts of parents, occasionally there's going to be a child who is not going to be thin, in fact is going to be fat. And the parents are just going to have to leave it alone.

"They cannot force that child to be thin, and if they've done the moderate things they simply are going to have to do what they can to make that child emotionally healthy, to know he is valued and talented and precious even though he and his parents might prefer that he be thinner."

Satter's program is based on what she calls "shared responsibility." It is the parent's job to provide food. It is the child's job to eat it in the amounts that satisfy.

As a general rule, babies know when they are hungry and parents should be prepared to respond. Nevertheless, Satter still sees pediatricians "telling parents to cut down on their children's food intake, not to let them get fat. And that kind of advice is really horrible for the feeding relationship.

"Too often the parent will haul their child in and say 'Get my child thin,' and the more that happens, the more the child gets the message that he's not any good unless he is thin . . ."

A recent example: A pediatrician suggested to a breast-feeding mother that the baby was "looking chubby" and that she was, perhaps, giving her too many feedings. He suggested cutting down from seven to five "or four if you can manage it."

"After two days the woman called up and said, 'This isn't worth it; it's wrecking our relationship. She's unhappy. I'm unhappy. If she's going to be fat, then so be it.' " Nevertheless, says Satter, the mother was left with an uneasy feeling that if the child became an obese adult, it would be her fault.

In fact, says Satter, few fat babies become fat adults, although overweight adolescents often do.

Most fat babies slim down after the first year or so and become perfectly normal toddlers. The popular theory that multiplying fat cells in infancy predicts adult obesity has not held up under scientific scrutiny. Satter cites some studies showing that less than 10 percent of infants who are obese become obese adults.

"The risk of developing adult obesity is increased to about 25 percent for the obese preschooler and 70 percent for the obese adolescent," says Satter. She also cautions that "unfortunately we really don't know how to go about prevention of obesity . Dieting doesn't work, and we don't know what does."

But "trying to lower the odds by withholding food is the worst possible thing," she says. "It causes more problems than it cures. If a child is threatened with going hungry they will become preoccupied with food and then they really will be inclined to overeat if they get the chance."

Another example: A patient who came to her with bulemia who described how her mother set out to underfeed her to guarantee her thinness, and by the time she was a toddler she was already sneaking food out of cabinets or the refrigerator.

"She wept," recalls Satter, "when she told me of her mother dishing up just a very small amount of food at the table and she knew she wasn't going to get enough to eat. And she cried because to her it felt like not getting enough love."

Under Satter's general program, structured meals and structured snacks can head off the kind of weight problems engendered by bad eating habits. She also believes in eating when you are eating, not when you are reading, watching TV, or otherwise engaged. Other suggestions:

* With toddlers who "won't eat," don't force or cajole. Eating or not eating quickly becomes a power struggle and nobody wins. Indirect techniques ("just come and keep us company for a few minutes") or just plain hunger will win out.

* Keep the cookie jar out of sight of panhandling toddlers.

* Offer water instead of juices or soft drinks.

* If a toddler seems hyperactive, consider whether he might just be hungry.

* Encourage exercise in children who seem too sedentary. For example, invent reasons for trips up and down stairs.

Basically, though, "You have to trust your child," maintains Satter, who has children, 16, 13 and 11. "As with everything in parenting you've got to walk that middle ground between being over-controlling and neglectful. You have to see they get the food, but then you have to turn it over to them. Parents are not able to dictate how much a child will (or should) eat and they shouldn't try.

"And they're not going to be able to dictate how his body will turn out, and they shouldn't try . . . But going along with what the child wants in food quantities is telling the child that his feelings are entirely acceptable and this is the supportive, caring and accepting kind of thing we're after in the parenting relationship."