One recent wintry morning, Bonnie Ruth Ervin, 34 and in poor health, climbed out of bed at about 3 o'clock, dressed, and went grocery shopping at an all-night supermarket where she was the only customer. It was a routine trip for Miss Ervin, who weighs 422 pounds and shops at twilight to avoid people staring at her.

For nearly 15 years as her weight has raced out of control, Miss Ervin, a welfare mother with two teen-age sons, virtually has dropped out of the mainstream of society. Except for her night-time shopping, trips to the doctor and rare visits with relatives, she remains a recluse inside her Baltimore home, constantly eating to drown her anxiety.

Doctors have warned her that her gross obesity is seriously impairing her health. Her high blood pressure is growing worse, her blood sugar count is on the verge of turning into diabetes and the arthritis that once was slight and localized is now spreading throughout her body.

"I really want to lose weight so I can lead a normal life again," said Miss Ervin. "But I can't seem to stop eating. I've been on diets - but I end up gaining back all the weight I lose."

Dr. Martin Valentine, who has treated Miss Ervin for several years, said her health is steadily declining. Her only hope, he said, is to shed fully half of her current body weight.

"Bonnie could drop dead any day from cardiovascular complications, the most common cause of death among obese individuals," said Dr. Valentine, an allergist and associate professor of medicine at Johns Hopkins University Hospital.

"She would benefit from vigorous exercise to help burn some of the excess energy," Dr. Valentine added. "But exercise for her at this point would only increase the risk of heart problems."

Miss Ervin, who was of normal weight 15 years ago, shares with millions her love for food, lack of nutritional knowledge and inability to resist her appetite. "There is a little bit of Bonnie Ervin in all of us," one doctor said recently.

Miss Ervin carried her excessive weight for years without experiencing serious health defects. But in recent times, the trips to doctors and hospitals have become more frequent.

Her breasts, which she says weigh nearly 50 pounds each, place an extreme strain on her spinal column when she is sitting or standing. When she is lying down she said the weight of her breasts causes her great difficulty in breathing.

In many repects, Miss Ervin is a classic study in the effects gross obesity can have on the human body. Although doctors continue to argue among themselves over whether obesity actually causes other illnesses, Miss Ervin's case strongly suggests a connection between her extreme over-weight and poor health.

According to statistics compiled by the nation's six largest health insurance companies, there is a direct correlation between the degree to which p person is over weight and the increased chances of a premature death from resulting health complications.

For example, it is estimated that a person who is 10 pounds overweight increases his chances of an early death by 8 per cent; 30 pounds of overweight increases the chances of premature death to 28 per cent; a person carrying 50 extra pounds has a 56 per cent chance of an early death; and a person as much as 90 pounds overweight has a 116 per cent chance of dying early.

If the Metropolitan Life Insurance Company's "table of desirable weights" is used as a standard, Miss Ervin is more than 264 pounds over the recommended weight for her age, height and the body build. By virtue of her weight, her chances of an early death has been increased by more than 200 per cent.

Bonnie Ervin, who is 5 feet 9 has not always been fat. In 1962 when she was 20 years old, Miss Ervin said she had a "decent shape" and weighed a trim 134 pounds, well within the recommended standard.

After a series of severe asthma attacks, doctors recommended that she take regular doses of Prednisone, an anti-inflammatory drug that greatly lessens the effects of asthma and various forms of arthritis.

Since her first dose of Prednisone, Miss Ervin said she has not had another serious asthma attack. But she said the drug did stimulate her appetite and radically altered her eating habits.

Dr. Valentine, who said he observed many other Prednisone patients, noted that although the drug does increase the appetite, but usually not enough to precipitate massive obesity.

Bonnie Ervin said her weak will power was no match for an appetite stimulant. When her appetite signaled her to eat, sheare. At first, she said her eating was in authomatic response to the drug. Later, eating became her only form of recreation, as it gradually eroded her health.

Miss Ervin dropped out of the ninth grade when she was 16 years old, and pregnant with the first of her two sons. Then she worked for several years as a counter girl for a drug store chain.

She gained weight rapidly after she began taking Predisone for her asthma. When she reached 200 pounds, she went to work as a nurse's aide in a private nursing home.

At 350 pounds, when she could no longer tolerate being on her feet for a full work day, Miss Ervin took a part-time job as a school janitor. Three months later her weight increased to 375 pounds and she found she was no longer physically able to work.

"I started getting and I had to stop. I was even having trouble just getting around in the building where I worked," she said. "I was already getting some public assistance. After I quit work, I had to go on the welfare completely." Miss Ervin, now receives a monthly allotment of $269.

Behind closed doors, Miss Ervin continues to do what her doctors have said will eventually destroy her life: she eats her fill. But for Miss Ervin, food and eating are the only luxury that her stark poverty still allows.

Not long ago, Miss Ervin said she lived on a steady diet of pizza, submarine sandwiches, spaghetti, lasagne, chicken and dumplings and hamburgers and milk shakes from fastfood restaurants.

Last year, worried about her health, she enrolled in the Johns Hopkins health and weight clinic, which takes its obese patients through a complete study nutrition, the causes of obesity, the illnesses that can result from overweight.

"I got disgusted on the first night I went," she said. "They tried to weigh me on the hospital scales but the scales only went to 350 pounds. I weighed more than 400.

"They told me I could go across to the hospital laundry and get weighed on the laundry scale or I could go home with one of the othe patients who had a scale that goes up to 800 pounds," she said.

In two months, Miss Ervin said she lost 40 pounds using the behavioral modification approach that encouraged the patient to base the consumption of food on its nutritional value and on the amount of energy needed for normal activity.

For two additional months, Miss Ervin said she was a patient at Baltimore City Hospital, where she was placed on a diet of 600 calories a day. In eight weeks Miss Ervin said she lost 70 pounds.

But in midst of her controlled hospital diet, Miss Ervin said her home was burglarized and she had to leave the hospital briefly to attend to that.

"When I went back to the hospital, they told me I couldn't get back on the diet. They said they were no longer taking Medicaid patients for treatment of obesity," she said.

"Unfortunately, most Medicaid programs do not consider obesity treatment a justifiable use of a hospital bed. Ironically, if a person has an illness which results from obesity, then he can receive help from Medicaid," said Dr. Valentime.

He said that hospital confinement may be the safest and only way that Miss Ervin will be able to lose weight and escape some of her health problems.

"We have thought about using bypass surgery (removal of a section of the small intestines which absorb nutrients from food during digestive process), but the risk is too great," he said.

"We could wire her jaws. But that is very dangeraous in a girl who has asthma," he added. "All that Bonnie really has that could turn her weight problem around is will power."

Although will power has not worked for Bonnie Ervin, it has been used effectively by William Heidel, 20, who has reduced his weight since last June from 400 pounds to 255 pounds simply by refusing to eat.

Heidel, who has been grossly obese for five years, said he first realized that his weight was a major health problem last April.

"I started getting sharp chest pains," he said. "I thought I was having a heart attack. The doctors told me that my overweight could lead to damage of my Kidneys, heart and circulatory system.

"They said that if I kept gaining weight, it would eventually kill me," Heidel continued. "In May I went to a commercial weight clinic. I was the heaviest in my class. Everybody else only needed to lose 35 or 40 pounds. I needed to lose nearly 300 pounds."

Heidel, who once worked as a chef in a spaghetti restaurant, was sent by his doctor to the Johns Hopkins University health and weight clinic.

"I like it at the clinic because there are some people here who are even heavier than I am," said Heidel. "Here the idea is to help us overcome the problem by discovering why we overeat."

After his initial consultations with a nutritionist and pyschologist, Heidel struck out on a low-calorie diet and immediately began losing about four pounds a week.

With each pound he is able to lose, Heidel said he becomes more and more proud of himself and his selfdiscipline. He has shed 10 inches from his waistline. "People don't turn and laugh now when I walk down the street. Now I can get into some decent clothes."

"Once when I weighed 400 pounds. I fell on the street," Heidel recalls. "No one could help me because I was so fat. I had to crawl on my hands and knees across the street to a fire hydrant to pull myself up. I don't ever want to be like that again."

Recently, Heidel gave a talk to patients at his weight clinic who have not been as successful as he. When he had finished, the group of about 40, mostly women, responded with loud applause.

"Bill Heidel, you've done more to sinspore this group than if I had passed out dollar bills," said Dr. Maria Simonson, director of the clinic, and an assistant professor at the Johns Hopkins Medical Institutions. "We would all do well to follow Bill's example.

"Don't come looking for sympathy," she added. "The key to controlling your weight is within yourself. I call it Heidel's Law.' That is, when food comes before you, you must learn to ask yourself, 'Do I want to lose weight or do I want toeat this food?'"