Not long ago, fresh Chinese vegetables were sold exclusively in Chinese grocery stores. In the regular supermarkets, bean sprouts were only in cans and snow peas were confined to the frozen food department.

Today, most well stocked markets offer a variety of Chinese goods. The produce section now features full heads of leafy Chinese or napa cabbage, flanked by the dark green thicker stems of bok choy. There are fresh snow peas, gingerroot, water chestnuts and bean sprouts. Finally, so it seems, mainstream America is being introduced to a diverse selection of fresh Chinese vegetables.

The Chinese classify vegetables into three main categories: root, leafy and fruit. Root vegetables include carrots, taro, daikon radish, bamboo shoots, water chestnuts, lotus roots, and ginger root. The leafy category extends to vegetables like cabbage, watercress, mustard greens and spinach. For fruits, the Chinese include tomatoes, eggplants, winter melon, bitter gourd and cucumbers.

To preserve the fresh flavors, crunchy textures, and vibrant colors of many of these vegetables, Chinese cooks favor methods like stir-frying, blanching and steaming. Traditionally, although these habits are slowly changing in the Orient, vegetables are not eaten raw for hygenic reasons, but they are frequently served cooked in cold salads and noodle dishes.

Eileen Yin-Fei Lo, author of "The Chinese Banquet Cookbook" (Crown Publishers, 1985), who lives in Montclair, N.J., is encouraged by the widening selection of Chinese vegetables available in supermarkets, but she still prefers to travel twice a week to Chinatown in New York City to purchase ingredients for her classes and family. In a telephone interview, Lo, who grew up on a farm in Canton, China, offered some valuable information on selecting fresh vegetables.

"I always tell my students that picking vegetables is like choosing a son-in-law," she says. "The same care and time must be used. Vegetables should be nice and fresh, have bright colors, with a smooth skin that's not wrinkled or yellow. When buying Chinese or napa cabbage, the whiter the color, the better the cabbage. And there should be no black or brown specks on the leaves. For fresh water chestnuts, you should squeeze them one by one to make sure they aren't soft or rotten. I store them in a brown paper bag in the refrigerator for up to two to three weeks.

Lo also offered several tips for cooking fresh Chinese vegetables:

Ideally, the vegetables should be cooked as soon as possible to preserve their fresh flavor. Don't buy them too many days in advance.

When stir-frying a firm vegetable like broccoli, cook it first until tender in boiling water and then immediately refresh in cold water.

Keep a bowl of cold water at hand near the stove and when a little moisture is needed, just sprinkle some water into the hot pan to create steam.

For stir-frying, heat the pan as much as possible before adding any oil. When adding the oil, add the minced flavorings -- like gingerroot -- with salt, at the beginning so it will coat the food.

The following glossary provides basic information on the most commonly available Chinese vegetables offered at well stocked supermarkets and at Chinese grocery stores.

Bamboo shoots: For some unknown reason, fresh bamboo shoot is rarely available here and the canned version doesn't compare to the fresh. Choose those marked "winter" bamboo shoot on the can for superior quality and always blanch shoots in boiling water for 5 seconds then refresh in cold water before using.

Bean sprouts: Most Americans are familiar with the standard bean sprouts which come from green mung beans. Chinese are also fond of larger soybean sprouts, which are found in most Chinese grocery stores. Soybean sprouts are cooked in stir-fried dishes, soup and stews. Mung bean sprouts may be served cooked in stir-fried dishes or uncooked in salads and cold platters.

Chinese broccoli: Chinese broccoli differs from its American cousin in both appearance and flavor. It is more slender and slightly bitter. Remove the outer skin and trim the leaves before blanching the thicker, more mature stalks in water.

Chinese cabbage: Bok choy, baby hearts of cabbage and napa are all members of the extensive Chinese cabbage family. Napa, with its broad, leafy head is more appropriate for dumpling fillings, soups, casseroles, pickles and stir-fried dishes. Tientsin or celery cabbage, a longer, less leafy variety, is popularly stir-fried, braised and cooked in soups. Bok choy, with its thicker stalk and leafy stems, is best stir-fried, in soups and casseroles. And the miniature hearts of cabbage are excellent stir-fried or in soups.

Chinese chives: Chinese garlic chives, available in Chinese markets sporadically throughout the year, have slender, flat leaves and a pungent garlicky flavor. Primarily, they are stir-fired, cooked in soups, or chopped and used in dumpling fillings.

Coriander (Chinese parsley): This flat-leafed parsley has a strong, slightly musky flavor. Keep it refrigerated with its roots in water and add it sparingly as a flavoring in soups, salads and cold platters.

Chinese eggplant: Chinese eggplant with its slender body and purple or white skin is sweeter and more tender than the larger, western variety. Select plump, smooth ones and use steamed, stir-fried or deep-fried.

Ginger root: There is no substitute for the fresh version of ginger, a tuber rhizome which grows underground. At different times throughout the year, a more tender "spring" version with a transparent skin and delicate flavor, is available. Choose smooth, plump roots and store them unpeeled in a jar or pot of sand.

Chinese mushrooms: Fortunately, fresh Chinese mushrooms are now available seasonally in most supermarkets. Fresh shiitake mushrooms, which have a slightly smoky flavor, are delicious stir-fried and in soups. In their dried form, shiitake mushrooms take on a more pungent flavor that is best considered as a seasoning. Oyster mushrooms, which are thick, meaty and somewhat mild in flavor, are delectable in soups, stews and stir-fried dishes. Enokiitake mushrooms, with their long stems and delicate caps, have an almost sweet flavor which is at its best in salads, soups or stir-fried dishes.

Daikon radish: This vegetable, with its long, white body and green stem is relished in soups, salads, stir-fried dishes, stews and savory pastries.

Yard-long string beans: The Chinese grow a variety of string beans that are longer and more tender than our western green bean. Stir-fried, deep-fried or served in a salad, yard-long beans have a lovely flavor.

Water chestnuts: As with bamboo shoots, the flavor of fresh water chestnuts is far superior to that of the canned. The tough brown outer skin should be removed before cooking and the meat should be blanched 10 minutes before using in a savory dish. Canned water chestnuts should be blanched briefly in boiling water as well to remove the tinny flavor.

Winter melon: As with most melons, the seeds and innards of this vegetable are removed before it is stir-fried, stuffed with meat or carved and served with soups. The flavor of the flesh is slightly sweet.

HOT AND SOUR CABBAGE (6 servings)

1 large head Chinese napa cabbage, weighing about 3 pounds

1 1/2 teaspoons salt

1/4 cup sesame oil

10 thin slices ginger root

3 to 4 dried red chile peppers, cut to 1/4-inch pieces and seeds removed

FOR THE SEASONINGS:

2 1/2 tablespoons clear rice vinegar

2 tablespoons sugar

1 tablespoon soy sauce

Separate the cabbage leaves and rinse lightly. Drain thoroughly and cut away and discard the stem portion of each leaf. Cut the leaves into 2-inch squares. Place the pieces in a bowl, add the salt, toss lightly, and let stand 20 minutes. Pour off any liquid that has accumulated and drain the cabbage pieces on paper towels. Place the cabbage in a mixing bowl.

Heat wok or heavy skillet with lid and add sesame oil. Heat until just smoking and add ginger root and chile peppers. Remove from heat. Cover for about 20 minutes, or until it reaches room temperature. Strain out flavorings, reserving the oil. Mix oil with the seasonings, stirring until sugar dissolves. Add mixture to cabbage and toss lightly to coat. Chill for several hours before serving.

STEAMED EGGPLANT FINGERS IN A SPICY PEANUT SAUCE (6 servings)

2 pounds Chinese eggplant or young Italian eggplant

FOR THE SPICY PEANUT SAUCE:

1/4 cup soy sauce

1/4 cup sesame oil

3 tablespoons rice wine

2 tablespoons smooth peanut butter

2 tablespoons Chinese black vinegar, or 1 tablespoon worcestershire sauce

1 1/2 tablespoons sugar

2 tablespoons minced scallions

1 tablespoon minced garlic

1 tablespoon minced ginger root

1 teaspoon chile paste

Trim the ends of the eggplants and cut them in half lengthwise. Cut the halves lengthwise into strips about 1/2-inch wide and 3 to 4 inches long. Arrange the pieces in two 10-inch quiche pans or pie plates. Place the pans in the bottom of two 12-inch steamer trays and cover.

Fill a wok with water level with the bottom edge of the steamer tray; heat until boiling. Place steamer trays over boiling water and steam for 15 minutes, or until eggplant pieces are tender when pierced with a knife. Reverse the order of steamer trays midway through the steaming. Let the eggplant cool slightly and transfer to a serving dish. Combine the peanut sauce ingredients and serve with the eggplant.

RAINBOW VEGETABLES IN A GARLIC SAUCE (4 servings)

3 medium-sized yellow or red peppers, rinsed, cored and seeded

1/2 pound fresh snow peas, ends snapped and veiny strings removed

FOR THE SEASONINGS:

1 tablespoon minced ginger root

1 tablespoon minced garlic

FOR THE SAUCE:

1 1/2 tablespoons safflower or corn oil

1 tablespoon sesame oil

1 1/2 tablespoons rice wine

1 cup very thinly sliced fresh shiitake mushrooms

1 cup 1-inch sections scallion greens

3 tablespoons soy sauce mixed with 1 tablespoon sugar

Cut the peppers lengthwise into matchstick-size shreds. Rinse the snow peas. Prepare the seasonings and mix.

Heat a wok or a heavy skillet and add the safflower or corn oil and the sesame oil until very hot. Add the seasonings and stir-fry 10 seconds until fragrant.

Add the peppers and the snow peas and toss lightly over high heat, stirring constantly. Add the rice wine and continue cooking for about 1 minute. Add the fresh mushrooms and the scallions and continue cooking for another 30 seconds. Add the soy sauce mixture.

Toss lightly over high heat for an additional 10 seconds to coat thoroughly and remove to a serving platter.

SAUCY GREEN BEANS (6 servings)

2 pounds yard-long string beans (If unavailable, substitute regular green beans and increase the cooking time slightly.)

FOR THE SAUCE:

1/4 cup soy sauce

1 1/2 tablespoons sugar

3 tablespoons rice wine

1/2 cup water

FOR THE LEEKS:

2 tablespoons safflower or corn oil

1 cup minced leeks or scallions

1 teaspoon sesame oil

Trim the ends of the string beans and cut them into pieces about 3 inches long. Combine the sauce ingredients.

Heat a heavy wok or skillet and add the safflower or corn oil. Heat the oil until very hot and add the leeks. Stir-fry for about 1 minute over high heat and add the string beans. (Add a little rice wine if the mixture is too dry.) Add the sauce and heat until boiling, stirring constantly. Turn the heat to low, cover and cook for about 12 minutes, or until the beans are tender. Uncover and turn the heat to high. Cook until the sauce has reduced to a glaze and add the sesame oil. Toss lightly and transfer to a serving platter. Serve hot, at room temperature, or cool.

From "Chinese Season" by Nina Simonds (Houghton Mifflin, 1986, $19.95)