When Clyde Lee went back to Culpeper High School for his 10th reunion last year, his classmates didn't recognize him. Lee, 6-foot-2, weighed 285 in high school. Since graduating he has lost almost 100 pounds.

"In rural Virginia, to be fat was to be healthy," says Lee, 30, a nurse at Washington Hospital Center. "We ate a lot of carbohydrates, pork and large quantities of food."

But when he moved to Washington in 1979, attitudes toward obesity were different and peer pressure convinced him to lose weight. Lee began to eat less and exercise more. At one point, two years ago, he got down to 175.

"It's a struggle," says Lee, who fights a daily battle to keep his weight at about 200 pounds. "I try not to let it get too much out of control before I do something about it."

Lee is among the millions of Americans who step on the scale each day and determine their mood and eating and exercise regimen by where the weight gauge lands.

Fear of fat can range from the healthy desire to avoid the hazards of obesity to the irrational terror of looking less than perfect in a bathing suit. But whether the pursuit of slenderness is reasonable or absurd, this mad battle against flesh has resulted in a society of people who are dissatisfied with their bodies and obsessed with losing weight.

Roughly half of all Americans are afraid of becoming fat, report three Old Dominion University psychologists in this month's issue of Psychology Today. In a survey of nearly 30,000 readers of the magazine -- selected to represent the United States' adult population in age and sex -- they found that 63 percent of women and 44 percent of men reported being afraid of becoming fat.

Americans, particularly males, are "considerably more dissatisfied with their bodies" now than they were in 1972, discovered Thomas F. Cash, Barbara A. Winstead and Louis H. Janda. The percentage of men who were dissatisfied with their overall appearance more than doubled -- from 15 percent to 34 percent -- compared with the results of a similar 1972 survey. The rate of women's dissatisfaction rose from 25 to 38 percent.

"Women are still less satisfied than men with their own appearance in all areas weight, muscle tone, upper torso, mid-torso, lower torso except face and height," the psychologists write.

Among their other findings:

Weight is central to body image. "Fifty-five percent of the women and 41 percent of the men were dissatisfied with their weight. Men were most dissatisfied with the mid-torso and women with the mid- and lower torso, the areas most often affected by weight gain."

A significant number of Americans are on diets. About 38 percent of the women and 20 percent of the men said they were on weight loss diets when they filled out the survey. Ten percent of the women and 6 percent of the men said they frequently resorted to crash diets.

Binge eating is common. Thirty-six percent of the women and 24 percent of the men reported that they sometimes go on uncontrollable eating binges.

Women evaluated themselves more negatively than men in appearance, health and physical fitness. Survey results "support the notion that women hold rather extreme standards for an acceptable body," the psychologists write. "As other researchers have shown, to the extent that women internalize a relentlessly thin standard to determine their attractiveness, they are left with two chances for a good body image, slim and none."

There are at least two rival theories on why people, especially women, have distorted body images, a University of South Florida psychologist reported in the same issue of Psychology Today. In most women "a perceptual defect may have prevented them from describing themselves accurately," writes J. Kevin Thompson. For about one quarter of women "the inaccuracy seemed to be based on their feelings rather than their physical problems in perception."

"More than 95 percent of women studied overestimate their body size -- on average one fourth larger than they really are," Thompson's studies show. In comparing his subjects' estimates of several physical features to their actual measurements, he discovered that women "overestimate their cheeks the most, followed by waist, thighs and hips . . .

"Two in five women overestimate by a large margin, perceiving at least one body part to be at least 50 percent larger than it is . . . Women also overestimated more than men did on their cheeks, waist and hips. Both sexes were equally inaccurate, about 22 percent, in overestimating the size of their thighs."

These distorted body images are not surprising in a culture that idealizes the thin, the young and the beautiful.

America's obsession with weight has become a $10 billion-a-year diet and exercise industry. In fact, the compulsion to be thin has begun earlier and earlier. Eighty percent of fourth-grade girls recently studied by a researcher at the University of California at San Francisco said that they were dieting.

"Parents are so preoccupied with weight that kids are picking this up," says Dr. C. Wayne Callaway, director of the Center for Clinical Nutrition at George Washington University Medical Center. "Kids are such good mimics." While dieting may not be "overtly encouraged" by parents, their behavior establishes a "perfect cultural role model."

This preoccupation with weight loss has accelerated over the last two decades. In 1978, Playboy centerfold models -- whose weight had dropped continuously since 1958 -- weighed 16 percent less than the average weight for women their age. In 1959, the centerfold models weighed 9 percent less than the average for women of their height and age, according to a study by Toronto General Hospital psychiatry researcher David M. Garner published in Psychological Reports in 1980. The weight of the models did not decline, because their heights increased; however, bust measurements decreased, waists became larger and hips smaller, he found.

Miss Americas have become thinner, too. From 1959 to 1978, Garner found, contestants showed an average yearly decline of about one quarter pound. Pageant winners showed an average yearly weight decline of about one third of a pound. In 1959, Miss America contestants weighed 14 percent less than the average for women of their age and height. By 1978, they weighed 23 percent less than average.

And thinness, apparently, pays off. Since 1970, the Miss America winners in this study weighed significantly less than the contestants.

For many people, weight determines state of mind. "Everyday standing on a scale is like spinning a roulette wheel," says Dr. John Foreyt, a clinical psychologist and director of the Diet Modification Clinic at Baylor College of Medicine in Houston. "When a wrong number comes up they feel depressed, anxious. If a right number comes up they feel good. But they never seem to lose that anxious feeling that they're going to gain it back."

Women are more prone to this "weight roulette" than men. "Women are more victimized by the media hype of being thin, looking thin, and being ideal," says nutritionist E.C. Henley, executive director of the Institute for Futuristic Health Care Delivery in Houston. "Men usually seek help to lose weight because it has to do with their health."

Fear of fatness has resulted in discrimination against the obese, studies show. Children as young as 6 described silhouettes of obese children as "lazy," "dirty," "stupid," "ugly," "cheats" and "liars," according to a study by J. Robert Staffieri of Indiana University published in 1967 in the Journal of Personality and Social Psychology.

Sometimes, health care providers share this prejudice. One study of 77 physicians showed that those surveyed described their obese patients as "weak-minded, ugly and awkward," reported George L. Maddox and Veronica Liederman of Duke University in a 1969 Journal of Medical Education.

This prejudice can mean discrimination at work, too. Overweight persons are considered to be less desirable employes than those of normal weight, even if their abilities are believed to be the same, according to a 1979 study published in the journal Sociology of Work and Occupations.

Each pound of fat could cost an executive $1,000 a year in salary, reports Industry Week magazine.

One reason weight is often such a major issue is that in the Unites States, food is loaded with more than calories. It is a way to express love, hate, control, anger, hurt. It's also used in a multitude of ways -- as a pacifier, reward, punishment, stress reliever, or to celebrate an important event or accomplishment. Hunger is often confused with being tired, lonely or bored.

Says nutritionist Henley, "Food ought to be a casual part of life, so it is not all-enhancing, all-encompassing."

Despite the false body image of those who confuse an extra five pounds with being fat, true obesity is a health problem.

Doctors and nutritionists who participated in last year's National Institutes of Health consensus development conference, "Health Implications of Obesity," agreed that body weight of 20 percent or more above ideal is a health hazard. More than 15.4 million American men and 18.6 million American women between 20 and 74 fit that description, according to the National Center for Health Statistics.

For those with diabetes, high blood pressure, heart disease, or their associated risk factors -- such as high blood cholestrol -- even lower levels of obesity can be hazardous.

Obese males, regardless of smoking habits, have a higher mortality rate from colon, rectum, and prostate cancer than non-obese males, according to the American Cancer Society. Obese females have a higher mortality rate from gallbladder cancer, postmenopausal breast cancer, and uterus (cervix and endometrium) and ovarian cancer than non-obese females.

Other research indicates that the location of fat on the body determines the degree of risk. Fat cells around the waist and flank (the side between the ribs and hip) and in the abdomen are more active metabolically than those in the thigh and buttocks, concluded the NIH conference report.

"Concentration of fat in the belly seems to be greater risk from a health standpoint," says Theodore B. Van Itallie, professor of medicine at Columbia University College of Physicians and Surgeons and director of the Obesity Research Center at St. Luke's-Roosevelt Hospital Center in New York. But scientists are not sure why.

The theory, says George Washington's Callaway, is that as fat cells in the belly get bigger they don't respond to insulin as well. The result may be the triggering of diabetes in those with a predisposition for it.

In contrast, fat around the hips, thighs, and buttocks poses less health threat. Says Van Itallie: "Women who have fat hips and thighs are not at risk from a health standpoint; they're mostly at risk from their own self-dissatisfaction."

Obesity affects longevity, too. "Obesity shortens your life span decidedly," says Dr. Benjamin T. Burton, associate director of disease prevention at the National Institute of Arthritis, Diabetes and Digestive and Kidney Diseases. "It depends on the person and the length of time you've been obese and the degree you've been obese."

Yet Burton and others caution that personal differences play a role in how risky obesity is. "There's always the individual exception," he says. "Some people can get away with things that other people cannot. In general, as you go into 30 to 40 percent over ideal weight, you're in real trouble."

While most experts agree that obesity is a hazard, there is some disagreement over what ideal body weight should be. Some say the various measures of ideal weight -- such as tables of average weights by height and age -- ignore critical individual differences. The NIH conference reported that neither the 1959 nor the 1983 Metropolitan Life Insurance tables for desirable weight by height reflect the current weight and mortality relationship for the American population. The 1983 tables allow for slightly higher weights, but NIH sug- gests that those at risk for high blood presure or type II diabetes should consult the 1959 tables, which have lower desirable weights.

People can be overweight and healthy, says George Washington's Callaway, pointing to those who come from families with a history of obesity and have an even distribution of fat and not too much belly fat.

"I'm not arguing that people should be fat," he says, "but we need ways of defining obesity other than weight-per-height tables."

He suggests that a person have a general physical exam to check blood pressure, blood sugar and blood fat levels. "If those are up, more often than not, it's appropriate to lose weight." People with a family history of these problems are advised to keep their weight down, he says.

Finally, he says, "If you gained weight in late adolescence or adulthood, you are probably at greater risk for diabetes, heart attack, high blood triglicerides and high blood pressure."

For most people, a realistic look in a in the mirror can indicate whether or not they are overweight. But stepping on a scale can be misleading.

The number tells you how much you weigh, but not how much of that weight is fat. "Obesity is an index of . . . the percentage of fat in the body," says New York's Van Itallie. "A person can be overweight and not be fat; you can be normal weight and be fat."

Adds Baylor's Foreyt: "There are thin people who are obese because their percent of body fat is greater than it should be."

Problems arise because people often confuse the terms lean and thin. Leanness is a measure of one's percentage of body fat. Someone who is overweight according to weight tables -- such as a muscular athlete -- may actually have a low body fat content because a great proportion of their body is muscle and muscle weighs more than fat.

Healthy men will have a body fat content of between 10 and 22 percent, says University of Houston physical education professor Andrew Jackson. Healthy women will have between 20 and 32 percent body fat. "Women on the average tend to have about 10 percent more fat than men ," says Jackson, who notes that females have essential fat in the mammary tissue and surrounding reproductive organs. Even if a women were starved, he says, she would still have 12 to 13 percent body fat, while a starved man would have only 2 to 3 percent body fat.

Underwater (hydrostatic) weighing in a hospital setting is a scientific way to determine percent body fat. During the process, a person is weighed while submerged in a tank of water. Using established equations, percent of body fat can be calculated. A more convenient way is to have a skin-fold test done in a physician's office or at a medically supervised diet modification center. For an accurate measure, three different skin-fold tests are done with calipers. Men are measured at the chest, stomach and thigh. Women are measured at the back of the arm, the hip and the thigh.

Even the weight-obsessed may find solace in knowing that while they may be somewhat overweight according to statistical tables, a body fat test might show that they are not necessarily fat.

Ironically, in a culture that encourages weight loss -- and promises that "you can never be too rich or too thin" -- our life style is a major reason for obesity, experts say. Our sedentary society is saturated with convenience foods, fast-food restaurants, elevators, escalators and little time to plan and prepare nutritious meals. Instead, we grab food on the run, devour business lunches, microwave frozen dinners, and consume cookies, cashews and carbonated drinks.

"We live in an obesity-promoting environment," says Columbia University's Van Itallie, "and society as a whole has to decided what to do about it, whether to teach people to resist the environment or change the environment or both.

"In a sense, they have to resist the environment they live in and create a substitute environment or select from their environment only those things which would encourage them to control weight."