Throughout her life, she's heard it repeatedly from her relatives and friends, even from strangers on the street:

"You have such a pretty face."

"On the surface it seems like a complicment," says California sociologist Marcia Millman, 33, who has continually struggled with excess pounds, and now weighs a plump 138.

"But what's insulting is the part that's left unsaid, but understood: "Too bad you're wasting it by being fat.'"

In "an effort to understand the meanings of being overweight," Millman, who has become somewhat of a crusader for the corpulent, conducted 50 in-depth interviews and dozens of shorter conversations with overweight people.

Her book, "Such a Pretty Face: Being Fat in America" (W. W. Norton, 252 pages, $10.95), is filled with anecdotes and analyses of the pressures, problems and plight of the overweight.

"It's horrible," she says, "to be fat in this society. Fatness is for us what sexuality was for the Victorians. There is something dreaded, forbidden, taboo about the subject.

"Obesity arouses emotions of surprising intensity, including horror, contempt, morbid fascination, shame and moral outrage. We seldom encounter a really serious discussion of these powerful feelings, nor any thoughtful exploration of why fat people are so stigmatized and excluded."

The most common excuse for aversion toward overweight people is "that it's unhealthy," notes Millman. "But smoking is much more detrimental to health, and we don't hate people who smoe.

"People with other health problems aren't condemned in the same ways. And many people have strong reactions to weight, even when a person isn't fat enough for health to be affected."

In a "fat-obsessed society" (where four out of every 10 people are clinically overweight), fatness, says Millman, is considered an expression of something basic about a person's character and personality.

"Our aversion corresponds to our own fears about ourselves. We look at someone who is fat and see a person who has gone out of control. Most of us have anxiety about losing control and it arouses these fears of self-indulgence."

Fatness is also a sexual issue, she says particularly for women. "If a woman is overweight, people think she's done it intentionally as a rebellion against society's pressure to be attractive.

"In our society fat women are viewed as unfeminine, unattractive, masculine, out of the running. Yet there is a countertheme that associates fat women with a forbidden, excessive, degraded or distorted sexuality.

"Since the oral needs appear to be great, perhaps the needs for love and sex are also insatiable."

This stigma isn't as great for overweight men, maintains Millman. "The emphasis on physical appearance for women is stronger. How many men do you know who will say they are fat if they need to lose 10 pounds? Women say it all the time.

"If a thin woman is dating a fat man people say, "That guy must be pretty good to get her.' But if a thin man is dating a fat woman, people say, 'Well that's probably all he could get."'

Millman says her own experience has proved "the world is kinder to a slim woman." While never obese, she has battled bulges for most of her life.

She has "at times felt tremendously frustrated and foiled at being unable to lose 20 pounds. And although I am tough . . . on occasion I have actually dissolved into tears when someone suggested that I should be on a diet.

"On the one hand it seemed silly to allow weight to cause me such distress, yet I also deeply resented what seemed an arbitrary and oppressive standard of normal weight and of what is acceptable and attractive in a woman.

"It takes a lot of energy and sacrifice to be very thin. If our lives are determined by weight concerns it takes us away from other pursuits."

It is unfair to assume, says Millman, that overweight people eat more than slender ones. "People who are fat early in life seem to develop more efficient fat-storage and may gain or maintain weight at a lower caloric intake than most people."

(Adds Dr. Maria Simonson, director of John Hopkins' health and weight program: "It's not fair to say all fat people are unhealthy. If a person is overweight to a resonable degree -- not more than 20 pounds above normal weight -- and they function well and don't have high blood pressure there's no reason they have to look like Twiggy.")

Despite her anger at societal stereotypes, Millman acknowledges that "clearly, in its extreme form, obesity is deleterious to health."

Another concern: "Fat people think their life will only start after they lose weight. They develop a double idenity -- the present fat one and the future gorgeous one. They postpone doing things that are important like getting a job, or making a relationship or buying clothes until they are thin."

Since "almost all diets fail in the long run . . . with weight loss maintained for at least two years in only 5 to 10 percent of the cases, this gorgeous future may never come."

And then there are the "people who lost weight and find it didn't make them happy. They may be surprised to find that they have new problems replacing the old."

Fat children, says Millman, "unlike most children, don't always get unconditional love. Parental love may be predicated on losing weight." As adults they may reject losing weight, "waiting to be recognized and loved for themselves despite an ugly appearance.

"And you don't have to be very fat to use weight to get a sense of control. A woman whose husband has withdrawn from her may gain weight so she can attribute his disinterest to the weight.

"Fat people often think of themselves solely from neck up. Their bodies are disowned, alienated, perhaps stubbornly present, but not truly part of the real self. This is reflectd in the aphorism, "Trapped inside every fat person is a thin person trying to get out."'

To thin folk who "feel repelled or hositle towards the overweight," Millman admonishes: "Try to get beyond seeing just the person's weight, and be aware how you impose stereotypes."

She urges the overweight to "avoid internalizing negative societal stereotypes. It's very important to communicate to other people that you respect yourself and expect to be treated with dignity."