The fear of getting fat is making some children and teen-agers eat so little that they stunt their growth, according to the leading article in today's New England Journal of Medicine.

The pattern is less severe than the extreme "anorexia nervosa" which makes some persons shun food, but may be far more prevalent.

"What I'm talking about is a boy, say, who doesn't really look terribly skinny. He may in fact look trim and slim, perhaps about 5 percent underweight. But he is underweight during a crucial growth period, and at age 14 or 15 may look like a 10- or 11-year-old," said Dr. Fima Lifshitz, a New York pediatric endocrinologist or specialist in hormones and growth, in an interview.

"I've seen a girl who was 16 when we first saw her and hadn't gained a pound since age 10," he added. "When we rehabilitated her and gave her enough to eat, she began to develop her breasts and other normal sexual and body characteristics for her age. But she has had little growth in height. She has had a permanent loss, because once women menstruate, they fuse their bones and don't grow more than another inch or two."

Lifshitz, Dr. Michael Pugliese and others at North Shore University Hospital on Long Island and New York City's Cornell University Medical College in the past two years have studied 201 Long Island youngsters with short stature or delayed puberty or both.

They found that nine boys and five girls--14 youngsters altogether, or 7 percent of these patients--had no hormone deficiency or other physical cause of their immaturity.

"All that was happening," said Lifshitz, "is that they weren't eating enough because they were afraid to get fat. Most of them were skipping meals, like breakfast--especially breakfast--and lunch.

"They didn't realize why they weren't growing and developing. Neither did their parents. In fact, some of their parents have refused to believe us when we told them the cause."

The problem, he said, is that a child should grow a couple of inches a year after age 4 "until adolescence, when you might grow even more, three or four inches a year in a growth spurt between ages 12 and 15 in normal boys and 10 and 14 in girls . . . . In a child who should be growing, a diet to keep a lean, trim, slightly underweight, a little less than ideal figure may not be sufficient for normal development.

"So the boys"--the doctors more often see boys, perhaps because boys are more growth conscious--"are also slow bloomers in sexual development, including body build, hair and moustache growth and shaving."

Slow development may not be the only problem, for "when you're undernourished, you're also at high risk for any number of medical problems, like infections."

The Long Island youngsters typically came from highly health-conscious upper middle class families, "the majority of them, not overweight, like many of us, very anxious to be slim and trim," Lifshitz said. "I think we've gone overboard on over-emphasizing this."