George Hamilton's approach to nutrition is biblical: He takes large doses of 10 vitamins and minerals for six days, and on the seventh he abstains. Wonder Woman Lynda Carter washes down her prepackaged eight vitamin and mineral pills with a gallon of sugarless lemonade. Sen. Strom Thurmond, 78, pops vitamins A, B, C, D and E at his office every morning. "They give me a little more zip," he explains.

These prominent Americans have joined other celebrities like author Judith Krantz and tennis pro Bobby Riggs and an estimated 20 million ordinary citizens in the astonishing and growing mega-vitamin craze. It is based on the controversial theory that large quantities of vitamins—up to 100 times the recommended dietary allowances—will bestow exceptional health and vitality.

Encouraging such a belief is Dr. Richard Passwater, 43, a Maryland biochemist and author of five best-selling books on nutrition. He claims that mega-vitamin therapy can not only add 15 years to a person's life, but also help prevent a shopping list of ills from colds to cancer. "No one under 80 should get heart disease," Dr. Passwater says, "and if you have enough vitamins and no genetic defects you can stop a cancer cell from ever forming."

Passwater's enthusiasm is not shared by many of his medical colleagues. "We all need vitamins," says Dr. Elizabeth Whelan, executive director of the American Council on Science and Health, a consumer-education group. "But just because a little is good doesn't mean a lot is better." Even Passwater sounds a cautionary note. "Not everyone's stomach can tolerate a sudden concentration of vitamins," he says, adding that mega-vitamin therapy should begin sensibly.

Passwater advises eight hours of sleep, plenty of exercise, no smoking, limited alcohol and a balanced diet with vitamin supplements that do not exceed the recommended daily allowances. Then, he says, "if you're interested in optimum health, think about supervitamins."

Of the 50 to 60 essential vitamins, minerals and amino acids that the body does not manufacture itself, Passwater thinks the following are the most important (in the dosages he recommends):

Vitamin A. Up to 25,000 IU (international units) daily. The RDA is 5,000 IU. Passwater warns that doses exceeding 100,000 IU may be toxic.

Vitamin B. An average 50 milligrams of each of the 11 different B compounds except B12 (50 micrograms). That is up to 25 times the RDA.

Vitamin C. 2,000 mg., as compared with the RDA of 60 mg.

Vitamin E. 400 IU; the RDA is 10. Selenium, an essential mineral. 100 micrograms; the RDA is no more than 200 mcg. Zinc. 25 mg., 10 mg. over the RDA.

Dr. Passwater's endorsement of vitamin B15 (pangamic acid) is his most provocative. It is not really a vitamin, but a mixture of chemicals and minerals that varies from one company's product to another. In a recent court case one of the best-selling brands, manufactured by FoodScience, was found to contain an unsafe food additive—dimethylglycine. One of the chief witnesses against B15 was Dr. Victor Herbert, president of the American Society for Clinical Nutrition, an organization of physicians and scientists. In laboratory tests Herbert found dimethylglycine to be a possible cancer-causing agent. "Passwater is talking nutrition nonsense," Herbert says. "B15 is a fake." Passwater rejects the charge: "The court was given misinformation." He predicts the case will be appealed on the grounds of new evidence.

Passwater is not without supporters in the scientific community, most notably two-time Nobel Prize winner and vitamin C proponent Dr. Linus Pauling, 79. He says Passwater is "reliable, with a good background and knowledge." Passwater, in turn, praises Pauling as "a genius and my hero." Another mega-vitamin therapy champion is Dr. Roger Williams, 87, a biochemist and former director of the Clayton Foundation Biochemical Institute at the University of Texas in Austin. Williams says he is "looking forward to a change" in the medical establishment's attitude. "They're coming along," he adds, "now that some of these vitamins are proving to be beneficial."

Passwater was born in Wilmington, Del., the son of a textile worker and a housewife. As a child he recalls "reading chemistry texts the way other kids read comics." Graduating from the University of Delaware with a degree in chemistry, he got his Ph.D. from Bernadean University in Las Vegas.

A biochemical researcher since 1959, Passwater runs the Solgar vitamin company's nutritional research center. In addition he tapes daily spots on health for two New York radio stations. The Solgar center is located a mile from Passwater's home in Ocean Pines, Md., where he lives with his wife, Barbara, and their two sons, Richard, 13, and Michael, 10. The entire family follows Dad's recommended mega-vitamin program. Even the Passwaters' poodle, Nepo, gets a high-potency multivitamin.

Passwater remains undaunted by the controversy over his theories. "There's no way you can take vitamins and say, 'Gee, I'm not developing heart disease today,' " the doctor admits. "You won't know that until 20 years later. But you will know about your energy levels. Your body chemistry will improve and you'll feel better. And," he adds, with a smile, "if it makes you feel better, do it."