The death last week of singer Karen Carpenter, which may have been linked to her battle with eating disorders, has prompted a flurry of frightened phone calls to area centers where anorexia nervosa and bulimia are treated.

Jerilyn Ross, senior clinical associate of the Compulsive Eaters Program of Washington, says she has heard from about a dozen patients who, she says, "were jolted" by the implications of Carpenter's death on their own situations.

"Our patients, quite frankly, are frightened," says Judith Asner of the Center for Treatment of Eating Disorders, "but some of them said that even though they were terrified, they rationalized that they were so worthless it wouldn't matter if they were dead."

Anorexia nervosa, compulsive self-starvation, and the binge-purge practice known as bulimia (from Greek word meaning "ox hunger") are related but separate eating disorders. They have become almost epidemic in the past decade, and bulimia especially has been an underestimated phenomenon largely because its victims do not look sick and because it is a closely guarded secret among its troubled practitioners. It is often seen in ballet troupes and among models, but occurs, specialists now realize, throughout the female population. (Most but not all victims of the two disorders are women and young girls.)

Only recently have victims of these life-threatening illnesses "gone public" with their problems. Actress Jane Fonda recently admitted to bouts of self-induced vomiting in the early days of her career. Most recently, Cherry Boone O'Neill, daughter of singer Pat Boone, has described her own anorexia problem in a book, "Starving for Attention," the latest in a series of public confessions about the conflicts of a cultural preoccupation with thinness, or, as one victim put it, "chocolate cake on one page and a diet on the next in every magazine you read."

A researcher in Chicago showed recently that Playboy centerfold models had become thinner, year by year, since the magazine's inception, and in one survey, even elementary school children indicated they believed "thin" was good and "fat" was bad.

Victims of anorexia or bulimia share a phobia about being fat, have seriously distorted perceptions of body image and low self-esteem, even though a typical victim is usually bright and often successful.Many anorexics start their compulsive diets after someone's casual reference to "chubbiness" or "pudginess" or "baby fat." It has been suggested that just such a passing comment in a concert review precipitated Karen Carpenter's problem. Anorexia nervosa usually is characterized by periods of self-starvation and compulsive exercise. The typical anorexic is visibly underweight and usually looks as though she is starving to death as, in many cases, she is. Nevertheless, she still sees herself not only as fat, but often disgustingly fat.

The victim of bulimia, sometimes called bulimarexia, is not perceptibly overweight or underweight. She is typically above average in intelligence and income, attending college or engaged in a demanding career. (The Journal of Behavior recently estimated that 10 percent of all female college students are seriously bulimic.) Bulimia is principally characterized by periods of binging (up to 10,000 calories at a time--a grocery bagful of food) followed by self-induced vomiting or excessive use of laxatives or diuretics or a combination. She typically guards her secret, even from husband or lover, for years because she is painfully, helplessly aware her behavior is "gross," yet not so gross as the fat she irrationally fears. For reasons still not clearly understood by therapists, the behavior becomes addictive. New discoveries about the relationship between food and brain chemistry are the subject of some study, as is the relationship of bulimia to hypoglycemia, a condition in which blood sugar is too low.

Anorexics are also known to engage in binge-purge behavior, but more often they simply fast for long periods at a time.

The end result of either syndrome can be weight control, of course, but also cardiac arrest.

Dr. William R. Ayers, medical director of the Georgetown Diet Management Center, which has a special program for eating disorders, explains that there can be two basic ways in which the heart is affected adversely . One, he says, is because "the heart muscle, like all muscles, requires basic nutrition," and when fat reserves are used up the body must convert protein to burn as energy.

The heart, Ayers points out, also has some special requirements that involve electrolyte balance--to keep it beating. The key electrolyte is potassium, interacting with calcium, magnesium and sodium.

In the process of normal digestion, the body converts protein into amino acids to break down nutrients. As the food is digested, these amino acids are reabsorbed as they pass through the intestinal tract. If the food is vomited before it leaves the stomach, these essential amino acids are lost, along with potassium that is highly concentrated in stomach acids. There can be further loss of protein through excessive use of laxatives, which speed the transit time of food through the system. Diuretics, which increase the excretion of fluids, cause dehydration and further loss of electrolytes. Any of these practices can weaken the heart, cause irregular heartbeats or eventually cause the heart to stop beating. Moreover, because stomach acids are lost, the body's acid-to-base ratio is unbalanced, which can be a long-term cause of incomplete digestion--and heart muscle damage--even when the abusive eating disorder no longer occurs.

"Of course," says Ayers, "the body has reserves in all these areas, but they are limited. There could be much individual variation . . . a person with a life-long problem clearly has much less margin of safety than someone with a recently acquired problem."

Dr. Michael Ebert, clinical director of the National Institute of Mental Health, who oversees a research program on eating disorders, notes that a study done by Dr. John Gottdiener, now a cardiologist at the Washington, D.C., Veterans Administration Hospital, demonstrated that "the size and muscle mass of the heart actually decreases" when the body is starved. Ebert emphasizes that "it is not nearly so much a danger when the victim is under medical care. It is a very serious disorder and this, the way Karen Carpenter died, is the way anorexia victims die--sudden death."