The Japanese pronounce it TOE-foo, the Chinese pronounce it DOE-foo, and the Americans are eating more of it every day.

Tofu is a bland, custard-like product that has been a source of protein in Oriental diets. Made from curdled soybean milk, it is also known as bean curd.

In the past tofu's use in this country expanded slowly but steadily with the growing popularity of Chinese and Japanese foods, which frequently contain cubed chunks of tofu. Now its sales are climbing sharply. "We project a 25 percent to 30 percent annual growth with virtually no promotion," says a spokesman for Quong Hop & Co., a South San Francisco firm that had been making tofu since 1906.

Tofu is showing up in "health foods" and on vegetarian menus; even non-Oriental American are making it commercially and developing ways to use it in Western dishes. It is available mainly at health-food stores and restaurants and at grocery stores operated by Chinese-or Korean-Americans. An occasional supermarket carries it.

Tofu's rising popularity in the U.S. results partly from the increase in the Oriental population on the East and West Coasts, but much of the demand for it is clearly coming from non-Oreintals. "Our program is to Americanize this food," says Thomas P. Timmins, president and sales manager of New England Soy Diary Inc., a two-year-old company here that is apparently the largest of nearly 50 tofu companies established by non-Orientals in the last three years.

The ambitious Mr. Timmins, who sometimes signs letter "Soy to the world!" likens the future of tofu to the present of yogurt, whcih was once obscure but now is virtually an American staple. He and Stephen Hassell, the company's chairman and product-development manager, envision a time when tofu is served in school lunches, deep-fired or grilled at fast-food stands and substituted for increasingly expensive cheese in hundreds of dishes.

No one is sure just how much tofu is eaten annually in this country, the amount is certainly small compared with meat and poultry-maybe even compared with parsley. Everyone in the industry, however, agrees with Mr. Timmins and Mr. Hassell that the sky's the limit.

"Our sales are increasing because a lot of people are learning to eat tofu for health reasons," says Shizuko Yamauchi, wife of the owner of Matsuda-Hinode Tofu Co. of Los Angeles, the nation's biggest tofu maker, with estimated production of 10 tons daily. Mrs. Yamauchi won't disclose figures.

Tofu picks up flavors easily and is often seasoned with soy sauce and garlic in traditional Oriental dishes. Its popularity as a health food developed after the January 1976 publication of "The Book of Tofu," a volume that famciers describe reverently as "a seminal work." The books sold 65,000 copies and has recently been condensed and reissued as a mass-market paperback by Ballantine Books. It lists hundreds of recipes for making vegetarian dishes with tofu and gives instructions for starting a tofu making shop.

The books inspired entrepreneurs to set up tofu shops in such unlikely places as Wichita, Tampa and Santa Fe. Among those inspired started the predecessor of New England Soy Diary two years ago.

The company now turns out nint tons of tofu a week, up from 500 pounds a week two years ago. It expects revenue of more than $750,000 this year. Mr. Leviton, who like many tofu fans has an almost evangelical zeal for the product, now is working to organize a trade group, the Soycrafters Association of North America.

At the Soy Dairy, tofu is made in equipment bought in Japan. Soybeans, grown organically, that is wihtout chemical fertilizers or pesticides, are soaked overnight in water. When they are at the right consistency, they are pureed in a grinder, mixed with water, steam-cooked, strained to remove pulp, and pured into a large tub.

Then comes the crucial step: A coagulant the Soy Dairy uses, imported Japanese nigari , the residue of sea-water desalination-is carefully hand-stirred into the milky-white soy liquid. Too little nigari will leave a watergruel. Too much will leave the tofu too bitter.

After it is stirred, the tofu is poured into rectangulat pans, and a heavy metal sheet is palced directly on top of it to compress it. It then cools and solidifies. After that, it is cut into one-pound chunks and the chunks are cooled with running water. Each chunk is then packed in a plastic tub with water; the water keeps the tofu from turning brown and developing a hard, inedible crust.

It is in such tubs that you find tofu in the refrigerator of your health-food store. Grocers who carry tofu generally keep slabs of it in barrels of cold water. You should keep tofu refrigerated after you buy it, the Soy Dairy says, and it normally should be eaten within a week of purchase.

Tofu comes in various styles, differentiated mainly by their water content. The Soy Dairy produces both a regular and a firm tofu. Some West Coast tofu makers produce firm and regular tofu and a soft tofu as well. Naturally, firm tofu, whcih contains proportionately more soybean solids and less water, has more protein and high nutritional value than regular tofu, and it costs a little more. It is also easier to cook with because it retains its shape when sliced or stir-fired.

Mr. Leviton, the tofu evangelist, stresses the variety of ways in which tofu can be prepared. In one pamplet he wrote, "Tofu can be grilled, fried, baked, steamed, boiled, scrambled, barbecued, marinated in sauces, crumbled raw in salads, added to soups, and used in many other food items, including casseroles, cheesecake, salad dressing and dips." While 80 percent of the Soy Dairy business now is with health-food stores and health-food restaurants, the company says that acceptance is spreading.

For example, Smith College of North-ampton, Mass., plans to test tofu on students this spring in a variety of dishes. "Most likely we will serve it" next year, says Stanley Rosko, assistnat director of food services. Nearby Hampshire College has been serving tofu for almost two years, mainly in cutlet form.

Two employes of the Soy Dairy demonstrate various tofu recipes to customers in stores. In the past, these demonstrations have generally been in health-food stores, but recently they have been welcomed by Stop & Shop supermakrets in Boston and Cambridge.

As people become more familiar with the product, new recipes keep appearing that use tofu as a substitute for meat or cheese. Judith Rubenstein, a consultant to the Soy Dairy who is pushing tofu to institutions, advocates using it as a substitute for more-expensive ricotta cheese in lasagna recipes. Mr. Timmins says he has received inquiries from kosher restaurants in New York about using tofu instead of cheese in blintzes.

Mrs. Rubenstein says she has been told of one New Englander who slices some tofu every morning, fries it in a skillet, douses it with maple syrup and eats it for breakfast like French toast. CAPTION: Illustrations 1, and 2, no caption