Since she was 11 years old, Marian Fineman of Philadelphia has been on some kind of diet. Although she has never been grossly obese, Mrs. Fineman, 48, and her parents before her have desperately sought ways to preventing her extreme overweight and its attendant problems.

In her 37 year odyssey in pursuit of the ultimate reduction plan, as her weight fluctuated widely, mrs. Fineman tried 20 different weight loss methods and doctors.

Mrs. Fineman, who has never weighed more than 183 pounds and has twice reduced to as little as 124 pounds, has over the years spend $14,288 to lose a cumulative total of 375 pounds - which averages out to about $38 per pound.

For 27 years, she was addicted to ampletamines, the powerful appeatite aupressant drugs that are in most "diet pills."

Last month before the U.S. Senate Select Committee on Nutrition and HUman Needs, Mrs. Fineman testified that she recently lost 46 pounds during a five-month use of the liquid protein-sparing fast diet. Already, she testified, she is regaining the weight.

Like baseball, motherhood and apple pie, dieting has become an indelible part of the American experience. There has in fact, developed a kind of "dieting syndrome," in which dieters usually lose weight, stay slim during a brief hiatus, and then regain all of the lost weight.

THere are 2,876 different methods of the weight reduction, including at least 2,000 diets, according to Dr. Maria simonson, assistant professor of biochemical and biophysical sciences and as assistant in psychiatry at John Hopkins University.

Less than 50 per cent of these methods are physically and mentally safe," said Dr. Simonson, who directs a health and weight clinics at John Hopkins. "Tre goal of most of them is to make money, not to improve the health of the obese person."

Each year Americans spend $10 billion on reduction plans. At any one time, an estimated 9.5 million U.S. citizens are dieting, according to Dr. Simonson. Only 29 per cent of them succeed in losing 20 or more pounds and only 6 per cent keep weight off permanently, she said.

The average dieter is healty, although slightly overweight. His quest generally is to halt his weight, keeping within a few pounds of the "desirable weights."

The search for reliable dietary information can be a trip through the "twilight zone" for people who want to know what is causing their overweight, how to guard against gaining and how to reduce.

Medical doctors tend to be short on insight into this major health problem. It affects million of American, but only in the last decade had te problem of obesity been sriously addressed by many medical schools.

"Ten years ago when I was in medical school, the problems surrounding overweight weren't even mentioned," said Dr. Norman Linenmuth, a physician with the George Washington University Health Plan. "Now there are lectures on the subject, but still not a full and seprate course."

Because of the lack of proper medical school training physicians, like members of the general public, have acquired much of their knowledge about obesity "in the street."

The multibillion-dollar business of diets and weight reducing has been left largely in the hands of laymen, who create and sell most of the weight control methods in American. By dieting stringently, many people have escaped the curse of obesity, only to discover that their health has been destroyed by dieting itslef.

Mrs. Fineman, who is a housewife and mother of two children, said her weight problem dates back to her childhood. "Even my baby pictures show rolls of fat," she said in her testimony. "When I was 6 years old, I remember feeling deprived because my parents would hide sweets from me.

"When I was 11 my mother took me to a doctor because of my weight problem. He prescribed thyroid extract and a low-calorie diet. He was to be first of 20 doctors and/or methods that I was to employ in my life-long struggle to overcome my affliction."

"I got started on a 27-year addiction to amphetamines at age 14. By the tine I was 17 I had developed hypertension," she continued. "At age 19 I weighed 165 pounds and then I managed to lose 12 pounds in two months in time for my wedding.

"At 22, after giving birth to my first baby I weighed 174 pounds," she said. "With the aid of a doctor's prescription medication, I managed to lose 47 pounds in six months. Then I gradually regained the poundage. I weighed 183 pounds following my second pregnancy, then lost 59 pounds. I weighed 124 pounds then, only to gain back most of what I had lost."

mrs. Fineman said she then tried hypnosis for 16 months and went from 170 pounds to 146. But again, when she stoppws the therapy, she quickly regained the weight.

"When I was 34, during a routine medical checkup I was found to have diabetes. I was told that if I wanted to live normal life span I must forever lose the excess weight," she said. "I immediately entered a hospital for a month of total fasting. This resulted in my losing 17 pounds of which I gained back 10 the following week."

Shortly, thereafter, Mrs. Fineman said she was admitted to the hospital for a leg infection. Mrs. Fineman said doctors were concerned that her leg might have to be amputated because of her diabetes.

"I stayed in the hospital an extra month for another attempt at fasting," she said. "I lost 17 pounds again the following week.

"When I was 35 I found psychotherapy and got weaned from amphetamined," said Mrs. Fineman. "Psychotherapy was a beautiful four-year experience during which I lost 25 pounds. But the results did not last. Between the ages of 35 and 45 I joined Weight Watchers on four different occasions, but with no satisfactory results."

Nine years ago, mrs. Fineman said she has her first attacks of gout, a form of arthritis characterized by fluid deposits in the hoints. Seven years ago, she said she began taking medications for hypertension.

"When I was 45 I joined a behavior modification program for the treatment of obesity," Mrs. Fineman said. "Although I had been dieting for the best part of 34 years, it was the first time that anyone in the medical profession showed insight and empathy into this demoralizing affliction of obesity.

"I lost 28 pounds during 5 1/2 months of behavior modification, and the weight stayed off much longer than with any of the other methods, but eventually I regained most of it," Mrs. Fineman said.

Last year Mrs. Fineman said she tried OA (Overseas Anonymous), an organization based on Alcoholics Anonymous principles, without success.

"Then I began the Protein Sparing Fast," she said. "I lost 46 pounds in five months, arriving at 124 pounds feeling very ecstatic and wonderful. I was able to stop all medication for diabetes and hypertension and gout.

"But once again I have begun to regain weight and I an now at 138 pounds and have had to start medication for hypertension again," she said, concluding her remarks.

"When a person goes on a diet, nobody - even doctors - knows what the exact outcome will be," said Dr. Albert J. Stunkard, professor of psychiatry at Stanford University and currently a visiting professor at the University of Pennyslavania. "Dieting is usually a provess of trial and error."

"There are a few predicters whihc we look at to get a general idea of how a patient and a certain diet will work out," added Dr. Stunkard, who recently published the book, "The Pain of Obesity."

"We know that men do better than women in weight reduction. When you're nervous and anxious, you don't do as well.

"We also have determined that if you lost weight on a certain diet before, you'll lose if you diet again," he said. "And if you failed before, you will likely fail if you try the same diet a second time."

The most common approach to weight loss is the traditional low-calorie diet, which usually is followed for a prescribed period with a goal of shedding a specific number of pounds.

Another popular method of weight control is medications that come in a variety of pills, powders and liquids that usually serve to temporarily suppress the appetite or substitue for certain nutrients in the diet.

In recent years, behavior modification has become a widely used approach to weight problems. "Behavior mod" is designated to get to the root of the overweight person's problem through psychoteraphy and nutritional education.

Dr. Lindenmuth, who said he counsels three or four overweight patients each week, has a simple philosphy about obesity.

"The onlyway you can become fat is by consuming more food than your body needs," said Dr. Lindemuth. "And the only way you can lose fat is by consuming fewer calories than your body needs."

Dr. Lindenmuth said that an individual can control his weight by making sure that his calorie intake equals the body's energy needs.

"If too much fuel is consumed, the excess is stored as fat and weight increases," he wrote recently in Vital Signs, a publication of the George Washington University Health Plan. "If too little fuel is consumed fat tissue is broken down to reclaim its stored energy, and weight decreases.

"Thus, all the food you eat has only two possible fates: to be burned as fuel or stored as fat," he said. "This is a basic law of nature," he said. "This is a basic law of nature (the conservation of energy) and can no more be defeated than the law of gravity."

Dr. Lindenmuth said that the key to successful weight reduction is ta closely monitor amount and the kind of food consumed, being carefully not to overload the dier with unwanted calories.

According to the National Academy of Sciences/National Research Council, the "reference" man aged 22 and weighing about 147 pounds should consume only about 3,000 calories a day.The "reference" woman 22 years old and weighing about 127 should consume a maximum of 2,100 calories a day.

Every pound of fat contains approximately 3,500 calories of stored energy, according to Dr. Lindenmuth. "In order to burn up a pound of fat, you must deprive your body of this number of calories," he said. "If you are able to restrict your intake of food sufficiently to deprive your body of 500 needed calories every day, you, you can expect to lose one pound of fat (3,500 calories) every week, and it will take nearly five months to lose a total of 20 pounds of fat (70,000 calories)."

Dr. John C. LaRosa, director of obesity research at George Washington University, said that there are about 200 calorie in one half cup of ice cream, two apples, eight ounces of fruit yogurt, two slices of bread, or two tablespoons of peanut butter.

To burn 200 calories, Dr. LaRosa said, it would require 40 minutes of tennis, swimming, golf (without a chart), or biking at five miles an hour.