Words of wisdom you won't find in Mao's little red book

''When the water goes 'glug, glug,' it is heated. . . .'' ''Use your fingers to stir - all the cooks in China do. . . .'' These comments are not from Confucius or from Chairman Mao's little red book. But to students in Lucy Lo's cooking classes in Hong Kong, they are just as wise and meaningful.

Mrs. Lo, an ebullient Hong Kong cooking authority, gives lectures and practical demonstrations regularly at the Towngas Centre in Causeway Bay.

Her classes, called ''Cooking With Lucy,'' are popular with local Chinese, resident foreigners, and tourists who want Chinese cooking lessons at the source - in Hong Kong.

Everyone likes her breezy style in both Cantonese and English, her enthusiasm , and her obvious skill in her field. She talks as she demonstrates, and it is difficult to tell which moves faster, her words or her cooking chopsticks.

As she prepares two dishes, moving from one to the other, she gives her students practical advice: ''Rub the steamed tofu bean curd with hoisin sauce with two fingers. Rub it as gently as you would your own skin.''

Her background information: ''The nicest bamboo possible comes from Taiwan. It has no holes.'' One of her poetic asides: ''Soy sauce - this is my life song!''

She also explains the origin of a particular dish. ''Tong Por Pork - that's named for Tong Por. He was a poet, and he liked good food.''

Mrs. Lo conducts her classes in a small theater in the Towngas Centre, a fact she finds amusing.

''Cooking demonstrations have a little bit of theater in them anyhow, don't you think? You must convey your own enthusiasm and show the novice that cooking is both fun and an art.''

With Mrs. Lo it is obviously both. Her round face is expressive, her throaty voice full of chuckles and wry comments. She tastes one dish as it nears completion, closing her eyes and murmuring, ''Beautiful!''

Each participation lesson lasts two hours; lectures are an hour and a half. During the class I observed, two dishes were prepared - Deep Fried Bamboo and Tong Por Pork.

Mrs. Lo works quickly, explaining: ''How can you be a good and quick cook? Experience and practice.'' Her own cooking began during World War II, when she observed and helped several professional chefs in Canton. She has been teaching for the past 12 years.

When the cooking is finished, students take plates and serve themselves from each dish, along with rice and tea. Most recipes taught are Cantonese, with a sprinkling of those from Peking, Shanghai, and other provinces.

''We are mostly from Canton here in Hong Kong,'' Mrs. Lo explains, ''and we don't like food spicy hot. If we cooked as they do in Sichuan, the Cantonese wouldn't eat it. That's why I cut down on the amount of chili pepper in a recipe. We don't need such hot food in South China.''

For information about Mrs. Lo's courses, write: The Towngas Centre, Leighton Centre, 77 Leighton Road, Causeway Bay, Hong Kong, or telephone Miss Chan, 5- 761535. A single demonstration lesson costs about $3.50. There are five other Chinese cooking classes, with other Chinese teachers.

This Peking dish is served at the Peking Garden restaurant in Hong Kong, but, as Lucy Lo tells her class, ''You can make it less expensively at home.'' Lucy Lo's Deep Fried Bamboo 4 6-ounce bamboo shoots, fresh or canned, in 1-inch slices 1 cup peanut or vegetable oil 2 to 3 ounces preserved cabbage leaves, shredded, washed, and dried 1/4 teaspoon powdered sugar 1/2 teaspoon sesame oil 1 ounce caramelized walnut, cut in pieces 1 large clove of conpoy (similar to shredded, dried scallops, available in a Chinese market)

If using fresh bamboo shoots, parboil shoots for 1/2 minute. Dry canned or fresh bamboo and deep fry it in 1 cup boiling peanut oil.

Deep fry cabbage leaves in same oil until crispy. Remove to a plate. Sprinkle powdered sugar and sesame oil over the cabbage. Toss lightly.

Sprinkle walnut bits and fried shredded conpoy or scallops over the top. Place bamboo shoots on top and serve immediately. Serves 4. Long Por Pork 3 cups peanut or corn oil 6-8 pieces bean curd, halved 3 1/2 cups water 1 1/2-2 pounds pork loin 1 large piece ginger root, shredded 4 tablespoon dark soy sauce 1 1/2 teaspoon sesame oil 2 tablespoons red rice paste 1 chicken cube 1 tablespoon sugar 8 ounces bamboo, shredded 2 stalks scallions, cut coarsely

Bring 3 cups cooking oil to a boil. Deep fry halves of bean curd until golden brown. Remove from oil, drain, and put on a large plate.

Heat 3 cups water to a full boil and add pork and shredded ginger. Parboil 3 minutes. Remove to a separate plate. Make marinade of 1 tablespoon soy sauce, 1 teaspoon sesame oil, and red rice paste and cover pork with it. Leave 10 minutes.

Measure 2 cups of oil (from that used for the bean curd frying) and bring almost to a boil. Deep fry pork in oil until golden brown. Drain, then steam over boiling water 2 hours or until tender. Cool, and cut into 2-inch squares.

Make sauce of 1/2 cup water, 3 tablespoons soy, chicken cube (mashed to dissolve it), 1 tablespoon sugar, and 1/2 tablespoon sesame oil. Mix well and pour over pork.

Put shredded bamboo and scallions in a deep, heatproof dish inside a steamer. Add pork and sauce on top, cover and steam for 1/2 hour. Serve hot. Serves 4. Braised Beef With Ginger 2 cloves garlic, minced 3 slices fresh ginger root, chopped fine 1 teaspoon sugar 4 tablespoons dark soy sauce 1/2 teaspoon salt 1/4 teaspoon black pepper 2 scallions, cut in 1-inch pieces 2 pounds chuck beef 3 tablespoons vegetable oil 3 cups water

Combine garlic and ginger root. Add sugar, soy sauce, salt, pepper, and scallions. Mix well.

Sear beef on all sides in hot oil in a heavy skillet. Remove meat from skillet and cut into 2-inch long slices. Return beef to skillet. Lower heat, add garlic mixture and continue cooking 3-5 minutes.

Bring water to a boil and add to beef. Bring to a second boil, cover, and simmer 1/2 to 3/4 hours or until beef is tender. Serve hot, with a side dish of boiled rice. Serves 6.

In the following recipe, Mrs. Lo uses pomfret. But equally good for deep-frying are bluefish, carp, halibut, haddock, mullet, sea bass, trout, whitefish, or pike. Fried Fish With Black Bean Sauce 2 lb. fish, cleaned, scaled, but kept whole Salt 1 tablespoon fermented black beans 1 clove garlic, minced 2 tablespoon dark soy sauce 1/2 teaspoon sugar 1 teaspoon peanut oil 2 slices ginger root, shredded 1/2 teaspoon salt 2 scallions, cut fine 2 to 3 cups peanut or vegetable oil 1 egg, beaten 2-3 tablespoon cornstarch

Wash fish and pat dry with paper towels. Score fish on each side with 3 diagonal slashes well spaced. Sprinkle fish with salt and rub it in.

Mix together fermented black beans and minced garlic. Mix well and add to soy , sugar, peanut oil, ginger, salt, and scallions. Blend well and set aside.

Heat 2-3 cups vegetable oil (enough to cover fish) in skillet or wok large enough to hold the whole fish.

Dip whole fish into beaten egg and then dredge in bowl of cornstarch.

Deep-fry fish over medium-high heat for 4 minutes per side, then turn heat high and continue frying 1 minute more per side. Fish should be golden brown, but be careful not to overcook. Drain and cover with black-bean sauce. Serve immediately. Serves 4.