WITH THE exception of blueberries, we naturally assume that food is just not blue. It is a wonder then, that the Southwest has been able to keep its secret so long. The word, though, is slowly getting out. In the land of enchantment, they eat corn that's blue.

Blue corn is a kitchen chameleon. The kernels, a deep bluish-purple, turn pale blue-grey when ground into masa harina or cornmeal. When mixed with water, the batter turns to teal, lavender under some lights. Griddle cakes fry up golden on the outside, turquoise on the inside; cornbread cooks into colorful layers. Blue masa harina has a coarser consistency than yellow or white and makes a more dense tortilla. The corn is said to be sweeter than any other variety when eaten fresh from the cob, although it is seldom served that way.

With the growing interest in regional cuisine and the national surge in the consumption of Mexican foods, it's easy to see why blue corn is going chic. Jane Butel, cookbook author and owner of the New York-based Pecos River Spice Company, sells blue cornmeal to Bloomingdale's in Tysons Corner and White Flint as part of her "Santa Fe Collection." And Ben Leon, business manager of Bueno Foods in Albuquerque, says he regularly ships blue corn products to a boutique in Long Island.

While easterners may make a collective face at the thought of blue tortilla chips with dip, Josie's Tortilla Factory in Santa Fe, N.M., is manufacturing 40 dozen eight-ounce bags of crunchy, corny and very blue tortillas chips a day, small potatoes compared with the 5,000 pounds of Doritos manufactured by one Frito-Lay factory every hour. And, says Leon, newcomers unaccustomed to the color sometimes conclude that his company's blue corn tortillas are outdated yellow ones.

It may, however, be too late for another blue food to make an impression on Americans. The supply of it is dwindling. Blue corn tortillas "may become extinct," says Ricky --Montoya, co-owner of Josie's Tortilla Factory, whose source of the corn--the local Indians--is uncertain after the next two years.

Blue corn is a story of bad timing. Just as the outside world is becoming interested, "the newer generations of Indians don't want to put up" with growing blue corn, says Frank Matta, supervisor of the USDA's Espanola Valley Experimental Station in northern New Mexico. There are only about 500 acres of blue corn growing in the United States, Matta estimates. (In 1982, the total U.S. acreage of edible sweet corn was about 620,000.) And it's grown in only three states other than New Mexico, says Matta--Texas, Colorado and Arizona. Apparently, the patches are primarily for the Indians' own needs. And because the commercial uses are as yet insignificant, sources in those states are hard-pressed to identify growers.

For centuries the Hopi and Navajo Indians have been growing blue corn originally brought from Mexico, but the "old ones have passed away," says Peter Casados, who grows probably the largest amount in New Mexico, a 50-acre plot where his family started growing it 100 years ago. The young Indian who grows up on a pueblo nowadays doesn't want to work on a farm; he has a 9-to-5 job. "It's so much easier to pick it blue cornmeal up in the grocery store," says Joseph Garcia, director of the state's Eight Northern Indian Pueblo Council.

Casados tells why. "It's a lot of work," he says. Blue corn is more difficult to harvest than the white or yellow. The stem is thicker and harder and Casados' six-man harvesting teams have to cut the corn from the stem with hatchets. No modern farm machinery is used. In addition, the yields are lower and the growing season longer.

All this makes blue corn expensive. Leon says he pays $8.50 for 100 pounds of white or yellow corn that he uses for his regular tortillas. The blue costs $22 for the same amount and the finished tortillas have about half the shelf life of the yellow.

Manufacturers such as Butel and Bueno Foods, who need relatively large quantities of blue corn, scramble to develop sources for it, arranging special contracts with Indian farmers. Montoya says she gets dried kernels from the northern New Mexican pueblos of San Felipe and Santo Domingo, where the Indians haul their 100-pound sacks to her factory and bargain for a price.

Madeline Jennings, a dietician at the Gallup Indian Medical Center in Gallup, N.M., who buys blue corn for the hospital, says that to some extent the supply in Gallup, where there is a "very large population of traditional Indians," hinges on the way it's still being sold through "traditional channels." The Indians who continue to grow blue corn still barter at trading posts, she said. So Jennings gets the hospital's supply from a feed-and-seed store, where the local Navajos swap their blue corn for other products.

While the restaurants in northern New Mexico serve open-faced blue corn enchiladas made with blue corn tortillas, the Indians have other uses for the corn.

Blue cornmeal boiled with water, seasoned with sugar or salt and made into a cream-of-wheat consistency is called atole, or mush. It is the Indian version of chicken soup. "It gives you strength. Everybody knows that," said one Indian employe at the Santa Fe Indian Hospital.

The dietician at the Los Alamos Medical Center, Sharon Smith, says that "a lot of patients won't want anything but it when they're feeling bad." Smith says she serves it to cancer patients, and frequently to diabetics as a late-night complex carbohydrate snack.

According to Jennings, the Indians categorize foods needed during the life cycle as weak and strong. Milk, for instance, is thought to be a strong food for babies, and weaker, or not as necessary, for adults. Blue corn is a strong food for all ages. Although there is "nothing medically proved about it," Jennings said, some patients ask for "the mush" three times a day.

Terrence Talaswaima, curator of the Hopi Cultural Center in Second Mesa, Ariz., says that blue corn, along with the white, yellow and red that the Hopis have grown for thousands of years, was given to them through "emergence" of the "earth spirit." Each color corn corresponds to the directions the Indians migrated--blue for north, red for south, yellow for west and white for east.

Cereal is only one way that blue cornmeal and water can be prepared. Although the process is a laborious one, the Hopi Indians still grind blue corn on a stone metate to make tiki, a paper-thin bread. Diluted with more water, it is made into a soup, or served as a drink. Some, like Leon of Bueno Foods, drink it in the morning instead of coffee.

Following are some sources and recipes for making blue food:

Bloomingdale's, White Flint and Tysons Corner. $3 for 12-ounce bag of blue cornmeal.

Bueno Foods, P.O. Box 293, Albuquerque, N.M. 87103. 505-243-2722. Sells blue corn tortillas and blue cornmeal. Write for a price list: Attention: Dorothy; or order by phone.

Josie's Best Tortilla Factory, 1130 Agua Fria, Santa Fe, N.M. 87501. 505-983-6520. Blue cornmeal ($1 a pound), masa harina ($1 a pound), tortilla chips ($1.21 for an eight-ounce bag). To preserve freshness, tortillas ($1 a dozen, without shipping charges) must be sent air-freight, which is expensive unless large quantities are ordered. Other orders must be prepaid for cost of item, plus 4.5 percent tax and $2 for handling. Freight costs are billed on arrival.

Peter Casados, P.O. Box 852, San Juan Pueblo, N.M. 87566. For one pound of blue cornmeal, send $1.25, plus $1.25 postage and handling. NAVAJO BLUE CORNMEAL GRIDDLE CAKES (Makes about 24 pancakes) 1 cup blue cornmeal 1 1/4 cups boiling water 1 tablespoon butter, melted 2/3 cup milk 1 1/2 tablespoons molasses 1 egg, beaten 1/2 cup all-purpose flour 2 1/2 teaspoons baking powder 1 teaspoon salt

Add cornmeal to boiling water and stir until blended. Add butter, milk, molasses and egg to the mixture and mix until smooth. Sift flour, baking powder and salt together. Add to the cornmeal mixture and mix until well blended. Spoon into pancakes and fry on a hot griddle until golden brown on both sides. BLUE CORN BREAD (8 to 10 servings) 1 1/2 cups blue cornmeal 1/2 teaspoon salt 1 tablespoon baking powder 1 cup chopped onion 1 cup sour cream 1/2 cup butter, melted 1 1/2 cups grated cheddar cheese 4 jalapeno peppers, minced

Mix together cornmeal, salt, baking powder and onions. Add sour cream and butter and mix until well combined. Pour half of the batter into a greased 9-by-9-inch baking dish. Sprinkle half the cheese over the batter, then the minced peppers, then the remaining cheese. Cover with remaining batter and cook at 350 degrees for 1 hour, or until a knife inserted in the center comes out clean. BLUE CORN CHEESE ENCHILADAS (Makes 6) For the tortillas: 1 1/8 cups blue masa harina or blue cornmeal 3/4 cup warm water, approximately For the sauce: 3 tablespoons olive oil 1/2 large onion, chopped 4 cloves garlic, minced 4 small green chilies, peeled and diced (or less to taste) 1 pound cooked, peeled and chopped tomatoes 1 cup tomato juice 1/4 teaspoon oregano 1/4 teaspoon basil 1 cup chicken broth 1 tablespoon cornstarch, dissolved in water For the filling: 10 ounces grated sharp cheddar cheese 1/2 cup sliced black olives 3 scallions, chopped Chopped parsley For the garnish: Chopped lettuce and tomatoes

To make the tortillas, toss masa harina or cornmeal and 1/2 cup water until mixture is well combined. Add more water if dough seems particularly dry and crumbly. Mix with the palm of your hand until mixture holds together, about 10 minutes. (The dough will not become smooth, but will be grainy and will separate when touched.) Set aside for about 30 minutes.

To make the sauce, heat the olive oil in a skillet. Saute' the chopped onion and garlic. When the onion is transparent, add the diced chili, the tomatoes, tomato juice and the herbs. Simmer for about 5 minutes, then add the chicken broth.

Dissolve the cornstarch in a little water and stir it into the sauce. Let it cook slowly for about 15 minutes. Sauce should be thick and pulpy.

To form tortillas, divide dough into 6 balls, each about 2 inches in diameter. If you do not have a tortilla press, place ball between 2 squares of waxed paper. Roll out to a 1/4-inch-thick circle 6 or 7 inches in diameter. Trim the edges if necessary. If using a tortilla press, place dough ball on waxed paper on tortilla press. Cover with waxed paper and press.

Carefully remove the top sheet of waxed paper and invert the tortilla onto an ungreased medium-hot skillet. As the tortilla becomes warm, remove the other square of waxed paper. When the tortilla is hot on top, turn on the second side and heat until it has a dry appearance, about 1 1/2 to 2 minutes. Repeat procedure for each tortilla. Wrap each in aluminum foil or thick toweling to keep warm.

To prepare the filling, place the cheese, olives, scallions and chopped parsley on separate plates. Place tortillas on an ungreased cookie sheet. Spread an equal amount of sauce over each tortilla and arrange the filling ingredients one at a time on top of it; first the olives, then scallions, then parsley, then cheese. Broil until cheese melts, about 2 minutes.

Place on plates and garnish around the edges with lettuce and tomato.

Adapted from "The Vegetarian Epicure"