"I'd been overweight all my life," said Phil Burke age 45, client of a Georgetown University diet control program. "In the past 25 years," he said, "I lost 1,000 pounds. Then I gained back 1,000."

Americans -- a generation of Phil Burkes -- are too fat and getting fatter. Despite a new nationwide passion for exercise, which should eventually take off some pounds only one group, white middle- and upper-class women past their 20s, have so far been getting thinner.

And the surgeon general is warning us: excess pounds are dangerous to our health.

Obesity "has reached epidemic proportions," say the medical experts, and too much weight remains "one of the most important medical and public health problems of our time."

The nation, it is obvious, is caught between its new passion for health, exercise and thinness and its still affluent, indulgent ways.

Who's fat in America?

One person in five is 20 percent above "desirable weight."

Women are fatter than men. Twenty-four percent of women and only 14 percent of men are obese.

Black women are heavier than white women. Poor women are heavier than affluent women, but affluent men are a bit heavier than poor.

Probably thanks to "better lives" and "better eating" -- actually meaning less physical labor and richer food -- men in their 20s are heavier, on the average, by 2 to 17 pounds (depending on specific age) than their 1959 counterparts. Men in their 30s and women in their 20s are 1 to 8 pounds heavier.

But women in their 30s have dropped a few pounds; women in their 40s and over up to 9 pounds.

"This trend has been going on for 40 years," Edward Lew, former vice president of Metropolitan Life Insurance Co., reports. "Men have put on weight at all heights and ages. Women over 30 are taking weight off because of fashion."

Charlotte Williams, 34, M.A. in public administration, American University, is black overweight and ambitious. In all these ways, she says, she is pressured by the new national passion for thinness.

"There is the pressure on every woman now to be a super-person," she said. "The whole American mentality is that you MUST be thin. You must be on a diet or you're not American.

"And there is special pressure now on a black woman to do well and look good."

Weight, plus or minus, is in part a class phenomenon. At the Fort Lincoln Family Medical Center in far Northeast Washington, nurse-practitioners and diet counselors Holly Markham and Joyce Smith see a legion of obese black women.

These largely middle-aged and elderly mothers and grandmothers grew up admiring the "fat, prosperous look" and the "fat, healthy baby." Only today are they suddenly being told, "Take it off."

"I think 90 percent of our patients are obsese," nurse Markham said. "It's sweets -- I love food!" explained one of her patients, a retired federal payroll check recently. This Mrs. A -- one of three women interviewed wanted their names printed -- had just lost 20 pounds in a six-week diet course.

Mrs. B, who lives on her Army widow's pension, had lost four pounds. Mrs. C had lost none. All three said their "problem" is just "eating wrong," eating starches, ice cream, cakes, pie.

True enough, but far from the whole story. Part of the problem is cultural. In several cultures, eating well means eating to be large. And the habits of the country persist in the city. "One woman told us of raising her family in North Carolina," nurse Markham said. "They were all up at 5:30 a.m. to work in the fields. Now they're here, but they eat the same way."

These patients also live on low incomes -- Social Security, pensions, welfare or wages. "We have them keep food diaries," nurse Smith said. "These high-price days, sometimes it's all bread.

"But when there's a holiday or family dinner, they eat. Not just a few things on the table, but turkey, chicken, pork, ham, potatoes, macaroni and cheese and three vegetables and desserts. That's what they're used to."

Dieter Charlotte Williams, a policy analyst for federal agencies, remembers that for a black girl there were few athletic outlets. "We didn't play tennis, we didn't swim. The boys could play basketball, but that wasn't encouraged for us. What was encouraged was cooking."

The result? Twenty-four to 40 percent of black women above the poverty line and 28 to 49 percent below it are overweight, compared with 19 to 28 percent of whites above poverty and 21 to 26 percent below. In each group, women above age 45 are the heaviest.

"The black women fighting to feed a family," says actuary Edward Lew, "is too busy surviving to worry about weight. She has more important things to worry about."

Yet poor black men tend to be thin. This too may be a class matter. Black men typically work at demanding, even demaging jobs, and their sickness and death rates are high. Perhaps only the lean and healthy survive. s

Still, not all poor are slim. In New York City, in a survey by economic class, a third of low-income men were overweight, compared with 16 percent of upper-income males. But the heaviest New Yorkers of all were the middle class.

In New York, this included many Jews, who are the most overweight Americans of all by religious group.

Sociologists say the reason is fairly obvious: "Here is a people who ate too little in Europe, and for them, just as for blacks, prosperity meant eating all you wanted." And the typical Jewish diet has run heavily to fat: meat, butter, cream cheese and chicken soup with lots of chicken fat "to make it taste good."

"The Georgetown University diet program makes you ask yourself, 'Why am I eating so much?'" said Charlotte Williams. "I had to face the fact that I sometimes used eating to compensate for other things. Sometimes it was easier to eat than vent one's frustrations."

Why do we get fat in the first place?

The surgeon general has a ponderous answer: "Large gaps remain in our understanding . . . [But] it is clear that obesity results either form ingestion of more food energy than the body needs or ultilizes, or the expenditure of less energy than normal."

Translation: We eat too much. We move too little.

For thousands of years men and women had to scratch for their food. The norm was too little to eat, not too much. "Only in the first few decades of this century did obesity become common," says Dr. Jerome Stamler of Northwestern University. "Until then the rich were the fat."

Today, most authorities agree overeating and underactivity cause 95 percent of obesity, and only 5 percent is caused by some hereditary, hormonal or other disorder.

Probably by training, not heredity, obese parents tend to have obese children. By most studies, obese children are three times likelier than slim children to become obese adults.

Though overeating is obesity's main cause, it is also becoming scientifically clear that losing weight is not equally easy for everyone. Women, for example, are fatter than men not just by habit or gluttony but because they have fatty breasts, thighs and buttocks for child-bearing.

Some scientists think overstuffed infants or adolescents develop too many "fat cells" -- adipocytes -- and the number of these cells stays constant for life making it harder for these "hypercelluar" persons to lose.

Also, it seems, humans and other mammals ages ago developed small stores of brownish fat cells to be burned off for warmth in hard weather. Some people may be more adept physiologically at burning this energy. Everyone knows the slim types who eat and never gain.

Many people plainly overeat because of emotional problems. Or frustration. Or boredom.

"For many, fat is a protective mechanism," Georgetown diet Counselor Mary Ellen Fediuk says. "It can be a mechanism for dealing, or not dealing, with disturbing people or social or sexual situations."

Then there is food as a symbol. Today almost evry human activity offers food as the centerpiece. The wonder, say some scientists, is that only a fifth of the populace is obese.

What is "desirable" weight? There are complex formulas bases on height, build and amount of body fat vs. lean. But if you look in the mirror and seem neither fat nor skinny, that's about it. "If you tighten a belt around your lower rib cage, then can't lower it around your belly, you're fat.

Is being just 10 or 20 pounds above average weight unhealthy? Probably not, though experts disagree.

There is little doubt that overweight is associated with diabetes, gallstones, degenerative joint disease -- ankles and knees worn out by sheer weight -- and high blood cholesterol and high blood pressure, which heighten the risk of heart disease and stroke. For women there is added risk of endometrial (womb) cancer.

Figures from the government's continuing survey of Framingham, Mass., indicate that "if everyone were at optimal weight," there would be 25 percent less coronary heart disease and 35 percent fewer blockages of brain vessels, causing strokes.

Georgetown University dieter Grazia Cramer, 43-year-old mother and part-time government researcher, said, "Have you ever been in a fat ladies' group? It's embarrassing. The majority are just mortified to be seen in a bathing suit. Some will go out only when it's dark."

"I need to lose and I'm doing it," Charlotte Williams said. "But I'm bigboned. I'll never be thin. And all you see in ads and on TV are these superthin folks."

Despite its dangers, do we over-emphasize obesity?

Do we make it too much a stigma for the millions whose only crime is eating the dishes life puts before them? Or too much a burden for those who try to diet and fail: the 75 to 95 percent of those in weight control programs who gain some or all of its back?

Some nutritionists, and some newly militant heavyweights, are asking these questions.

Obesity, it seems clear, has become not just a health problem but a national neurosis. This is especially true for women, said Mary Ellen Fediuk, who administers the Georgetown diet center.

"Men come in for health," she said. "Women come in for appearance. And today a lot of them fear that if they're fat, they won't get ahead on the job." t

Indeed, say many persons, fat women are discriminated against; fat men less often.

Many young women are even becoming mentally ill anorexics, who waste away because they won't eat enough. Some alternate between binges of gorging and starving; when they do eat, they often lose their food in helpless spasms.

Their revulsion, it seems clear, is born of perplexity over our worship of thinness, on the one hand, and our piles of hamburgers, pizzas and sugar-loaded drinks, on the other. "It shouldn't be a crime to be fat," counselor Fediuk said,

What can we do to improve this nation's health by improving its waistlines, without adding to the guilt the fat already feel?

Nutrition authorities have no easy answers. They say they can only tell us the facts, and hope for more tolerance. At the same time, they add, dieters and, counselor Fediuk believes, "more people are beginning to make it."

The so-called 75 to 95 percent "failure rate" ignores the pounds that remain off, even though they may not be "enough." And many dieters, like many chronic patients, may have to work at the problem all their lives.

"In some ways we're overconcerned, yes," Dr. William Ayers, the Georgetown program's medical director, said. "But I think that medical profession is underconcerned."

Many doctors, he said, are understandably discouraged because they "tell their patients to lose and they're ignored." Yet "you can't just hand out a diet sheet and drop the subject. It takes more sophisticated counseling over time, perhaps a long time. It often takes psychological help. If doctors abandon that role, others will fill it. That's why there's such a proliferation of fad diets and weight loss clinics. There's a big buck to be made."

Diet pills? Most doctors are unimpresed with them. The "best" diets -- those most effective in the long run, authorities say -- include almost all foods and nutrients, though special diets may be needed for a time for some persons, who should then be under close medical watch.

In short, the best and most scientific diet advice for most people turns out to be the old, sensible advice: "Moderation."

"There years ago, after years and years of high blood pressure and emotional suffering, I entered the Georgetown program," dieter Phil Burke said. "I started exercising. I'm deputy executive secretary of the Bicycle Manufacturers Association, so I cycled. In six months I got down from 264 to 184, then 173.

"I couldn't maintain that low a weight. But now I cycle, I run. Now and then, when I'm tense, I go the dessert route. But I have abolished butter, salt and soft drinks. Now I fluctuate around 200 or 205. I'm not skinny, but I feel wonderful."