In pursuit of the perfect body, thousands of people, mostly women, are swallowing (quite literally) gallons upon gallons of a red (or orange) liquid which is pre-digested protein.

Most of the people on this protein-sparing fast diet which is said to result in dramatic weight losses of 20 to 30 pounds in a month are eating nothing but the liquid protein three times a day. Some are using it for two meals and eating regular food for the third. They lose less weight.

When this diet is followed under strict supervision of a physician, it is probably safe. When dispensed at the local drug store, with no more than a sheet of instructions, as it is to thousands of people, it can be dangerous.

Experiments with liquid protein as a weight-reducing aid have been carried on at Case Western Reserve University in Cleveland and at Harvard, but it was Dr. Robert Linn who popularized the diet in his book, "The Last Chance Diet."

Dr. Linn, an osteopath who lost 65 or 70 pounds on the diet, began his weight-reduction practice in Philadelphia. Early this year he opened an office in Washington, partly to accommodate many wealthy Washingtonians who had traveled to his Philadelphia office weekly in order to participate in his program. The initial visit is $100 and weekly costs for the liquid protein, the vitamin and mineral supplements and office visits are $60. Dr Linn claims patients because they have kept off their weight for a year.

At least one other physician in town, Dr. Monroe Romansky, also treats patients with his own chemical formula similar to the one used at Case Western Reserve and vitamin and mineral supplements. Dr. Romansky is not prepared to say what the success rate will be at this point.

Before starting the diet under medical supervision, a complete physical examinationis required to ascertain if the patient has any physiological problesm which might be aggravated. During the diet the patient is monitored each week to be sure that none develops.

A diet of these liquid amino acids can throw the body's chemistry out of balance. Generally pregnant women as well as those with kidney problems and malfunctioning livers should not be on the diet.

One of the physicians who developed the program, Dr. George ZBlackburn of Harvard Medical School, said in a magazine interview: "Our major concern is that people will undertake to follow this program on their own. This could be hazardous."

But none of this information has stopped people from buying either Dr. Linn's Prolmn or similar formulations off the druggists' shelves. Some places sell it with a sheet that gives some vague directions for use. Others sell it without any information about potential hazards.

The Apothecary in Bethesda, which sells a product called Pro-Vita for $12.50 plus a vitamin supplement for $9.50, warns potential dieters on an accompanying shet of paper. "It is most important that you are in good health and have no kidney problems or gout."

it explains what to do if a buyer experiences some of the minor side effects of bad breath, constipation, muscle cramps (buy potassium supplement) and says to eat one meal a day consiting of a "satisfying serving" of fish, poultry or lean meat, eggs or cheese and a small serving of certain vegetables. It says to refrain from eating any sweets, starches and alcohol. Many people who need to lose weight have no idea of what constitutes a "satisfying serving" or a "small serving."

Atone Rodman's on a recent Sunday, when the liquid protein had been on sale for $7.99 a quart, there was no literature available. A pharmacy counter employee said the literature "isn't very good. The best thing to do is buy the book (Dr. Linn's) and see a doctor. You shouldn't do this without a doctor," he said.

Most of the containers themselves contain very little information or directions for use, and either no warning at all about the need for medical supervision or very vague ones. The old Linn formulation (he has a new one he uses in his offices now) that is sold in drug stores carries the following warning on the label: "Prolinn may be used as an aide to weight reduction as directed by your physician. Keep out of reach of children."

According to diet specialists, the saving grace for the diets without doctor's supervision is the consumption of the one regular meal a day that most of the protein supplements recommend. With a regular meal-dieters are less likely to do serious harm to themselves by causing a latent condition to flare up.

In addition to vitamin and mineral supplements some patients need varying amounts of potassium. According to Dr. Romansky, they must also drink large quantitites of fluids each day. But one of the products sold as "a nutritional aide to healthful weight reduction," NaturSlim, says the opposite. The directions accompanying the product say to "avoid extra liquid between meals" for the first four days. Without medical supervision, those on the protein-sparing diet can become extremely confused.

Writing in the October 1976 issue of Family Circle, Dr. Linn said: "The protein-sparing fast is a medical program. It's imperative that the doctor know what the patient is medically."

Accompanying Dr. Linn's article were comments from an obesity specialist, Dr. Leonard Haimes, who is president of the American Society of Bariatric Physicians. Dr. Haimes emphasized the importance of pursuing the program "under close medical supervision . . ."

Dr. Haimes also stressed that the diet is "only part of a change in one's lifestyle that must be accomplished in order to have a successful, meaningful maintenance program. The lifestyle changes must include nutrition education, behavior modification, exercise and some method of stress reduction in order to have a lasting result."

Dr. Romansky said: "Diet behavior modification is a very important part of the program. Otherwise the person is likely to go back to his or her old eating habits once the diet phase is over and gain back all the weight which was so difficult to get off."

Asked if he worried about people buying Prolinn off the shelf and using it without seeing a physician, Dr. Linn said: "You can't sell it just directly to doctors because they aren't tuned in to obesity. If you make it too much of a problem for them, they are not going to be so willing to do it.

"We want doctors to utilize the program. The patients can get them to do that.

"I think it is necessary to have my name on it - I don't like it - but it's necessary."

Why it is necessary for Dr. Linn to have his name on as over-the-counter protein supplement is unclear. There are so many others. But there may be another factor in Dr. Linn's decision to sell Prolinn through drug stores. Last December, the New York State Attorney General. Louis Lefkowitz, charged a retail-book store with misleading advertising in connection with Dr. Linn's book "The Last Chance Diet."

According to the Attorney General's office, Walden Book stores' ads were misleading because "they failed to disclose that the use of a protein liquid formula called Prolinn was an indispensible part of the described diet adn that this liquid per se, cannot be obtained except through the author, Dr. Linn."

Walde Books agreed to make a refund to any purchased of the $10 book who wanted it.

In order "not to get into an ethically sticky situation" with the profits from the over-the-counter sale of Prolinn, Dr. Linn said he has donated the trademark Prolinn to the Nutrition Research Foundation, an organization he set up in August 1976. The profits from the sale of the formula go to the non-profit foundation. Last Friday the Foundation raised additional money at a benefit dinner and fashion show held at the Ivory Coast Embassy. According to a foundation press release, its purpose is "the study of current issues relating to nutrition and obesity." Dr. Linn said earlier in the year that a symposium had been planned for the spring, but none has been scheduled yet.