In the late '60s when she was an impoverished New York actress, Lisa Tracy discovered vegetarianism. Vegetables and grains were cheaper than meat, and the wisdom of the day held that they were healthier, too. So Tracy began to follow what she calls a "rudimentary form of macrobiotics" -- trying to get all her nutrients from a complex mixture of grains, legumes, beans and vegetables.

The diet was too strict, and eventually she "fell off the wagon." In the mid-'70s she tried again, this time allowing herself plenty of milk, cheese, eggs and a little fish. But even that didn't last.

So Tracy, now an editor at The Philadelphia Inquirer, decided to approach meatless eating in three stages. Stage 1 -- drop red meat; stage 2 -- drop chicken; stage 3 -- drop dairy products. "Right now I'd say I'm between stages two and three," says Tracy. But it's important, she feels, to be able to shift between stages without guilt.

Lisa Tracy's experience, which led to her new how-to book, "The Gradual Vegetarian" (M. Evans and Company, $17.95), probably mirrors the experience of millions of would-be vegetarians. Most people don't have the willpower to live an entirely meatless life, even if they wanted to.

But a growing number of semi-vegetarians -- people who eat less meat, more vegetables -- are becoming a decisive force in shaping the nation's taste in food. And it's possible that their way of eating may be the healthiest of all.

Gallup surveys done for American Health show that semi-vegetarianism is a trend. Late last year, in a survey on the impact of the health movement, Gallup found that 24 percent of those polled now eat less meat than they used to. When applied to the U.S. population, that's 40 million adults. And fully 44 percent eat more fruits and vegetables.

Now a second-stage poll on food habits shows the reasons for the shift. Gallup phoned 1,033 Americans in January to ask about their dietary beliefs. Right away, they made it clear they are not hard-line vegetarian purists. Only 3.7 percent of Americans now G say they consider themselves to be vegetarians.

But tens of millions of Americans, the new survey shows, agree in principle with the movement away from meat. A clear majority, 52 percent, believe that "no one really needs to eat meat more than once or twice a week." More than one-third (37 percent) believe that "vegetarians are probably healthier than most Americans." And a majority of 72 percent disagree with what used to be the standard notion: "The vegetarian diet -- one without any meat, poultry or fish -- is just a fad that will pass."

Nutritionists and doctors have studied vegetarians, and found that they're generally well-nourished -- and have less chronic disease than the rest of the population. Doctors have recently tested vegetarian diets as a treatment for heart disease, hypertension, early-stage kidney disease and other ills. And they've told the whole population to eat more complex carbohydrates, less protein and less fat -- in other words, a semi-vegetarian diet.

The health evidence is so persuasive that it's become the main motivation for new converts to vegetarianism. That's a change. Most people used to become vegetarians "to solve the world hunger problem, or for spiritual reasons or animal rights," says Paul Obis, founder and editor of Vegetarian Times magazine of Oak Park, Ill. But now, he says, health has become the number one reason his readers have given up meat.

If it were just healthy, like cod liver oil, meatless fare wouldn't be catching on. But today's vegetarians have also shown that meatless meals don't have to be ascetic.

Vegetarians are now producing a chic, fresh, tasty cuisine that even semi-vegetarians can enjoy. The hottest meal ticket in San Francisco is Greens, a gourmet vegetarian restaurant that has offered such delicacies as zucchini fritters with tomato sauce and sliced avocado; Swiss chard and spinach soup with parsleyed creme Chantilly; an Alsatian Gruyere and cumin tart; and strawberries in puff pastry for dessert.

Even some airlines are now creating good-tasting vegetarian meals, and United reports that requests for meatless dishes have quadrupled in the last few years. Perhaps most important, vegetarian cookbooks have undergone a renaissance. There are now books on Chinese, Indian and Italian meatless cookery, and home-grown best-sellers with rich illustrations and gourmet recipes. Among the most popular authors: Madhur Jaffrey, expert on Eastern cooking, and Californian Mollie Katzen.

Finally, just as vegetarian recipes are getting more popular, so are "vegetarian" foods -- soy products developed as meat or dairy substitutes. Some food marketers believe that tofu (derived from soybeans) may soon become as popular a "health food" as yogurt. One tofu product -- the ice-cream substitute Tofutti -- has already become so popular that Gloria Vanderbilt has come out with her own designer brand of tofu: "Glace." And David Mintz, the millionaire inventor of Tofutti, is diversifying into tofu burgers, tofu sauces and dressings, tofu pies and tofu egg rolls.

Vegetarians have become our nutritional pacesetters by bringing together health and taste in a new way. It's a recent match, and one that became possible only with changes in nutritional knowledge.