Celia Casey, a graduate of the Cordon Bleu in Paris, is offering a series of Tunisian and Moroccan cooking classes at the Alliance Francaise, 2142 Wyoming Ave. N.W. Demonstrations include the techniques of making Bastila, Couscous Tunisien, Tajine de Poulet and Couscous Marocain, among others.The two-hour demonstrations began Jan. 31 and are $15 per class. Contact the Alliance Francaise for registration and information (234-7911)

It's midnight at the oasis

The camels are in the shed

A crescent moon hangs in the starry sky

And everyone is in bed

Dreaming blissfully of the

Wonderful couscous they have just been fed

This particular oasis is in Tunisia, a sparkling, fertile emerald in the crown of North Africa. It offers one of the most healthful, varied and lesser-known cuisines in the world.

Couscous, the staple dish, is of Berber origin. The base consists of finely ground and steamed durham wheat or semolina. It is served with an infinite variety of soups, stews and sauces, from savory to sweet. Some of the most popular contain lamb or chicken, but many of the coastal towns prepare a rich and spicy couscous made with fish soup and vegetables.

This is the perfect dinner to serve a group of fish fanciers. The secret of success is to cook the freshest fish obtainable in the gently simmering soup for no more than five minutes just before serving. Delicately fried fish cakes, perfumed with mint, accompany the feast. Serving instructions follow the recipes.

In North Africa, couscous is prepared in a tedious manner from milled semolina. A few drips of oil are placed in the coarse flour and stirred with the fingers. As the grains collect in balls, they are broken down until each individual grain is coated with oil.

With pre-cooked or "rapid couscous" found in the gourmet sections of many area supermarkets and all Middle Eastern markets, this first step has been completed and the grain only has to be soaked and steamed. There are several different brands available from France, Morocco and Tunisia.

A couscousier is the traditional pot used for preparing this meal. It consists of two sections, the bottom is rounded and holds the soup or stew. The top section is for the grain. It is like a sieve with large holes. The top half fits snugly into the bottom half. Couscousiers are available at most area gourmet cooking equipment stores and some Middle Eastern markets.

An improvised couscousier can be made by placing a cheese cloth-lined colander over a large pot containing boiling water. In either case it is extremely important not to allow the soup or water in the bottom section to touch the top section.

COUSCOUS (6 to 8 servings) 2 pounds (2 packages) couscous 6 cups water Salt to taste

Moisten the couscous with salted water. Let stand for 10 minutes or until the grains swell and all water is absorbed. Rake with fingers to remove any lumps. Place in sieve section or colander over boiling water and steam for 20 minutes. Turn out on a large plate. Rake again to remove any lumps. Return to sieve and steam for another 20 minutes. Remove all lumps before serving.

FISH BOULETTES (Serves 6) 2 pounds fish filets, coarsely chopped (rockfish, sea bass, cod or halibut) 1/2 pound stale white bread (soaked in water and well drained) 3 large eggs 3 tablespoons finely grated onion 1 teaspoon crushed dried mint leaves, or 2 tablespoons finely chopped fresh mint leaves 1/4 teaspoon white pepper Salt to taste 1/2 cup vegetable oil

Combine fish, bread, eggs, onion, mint leaves, pepper and salt. Mix with hand until throughly blended. Shape into balls. Heat oil and fry fish balls until golden brown.

THE BOULLION OR FISH SOUP (6 to 8 servings) 1/2 cup vegetable oil 2 medium onions, sliced 2 cloves garlic, crushed 1 can (6 ounces) tomato paste 2 whole tomatoes, peeled, chopped and seeded 4 medium potatoes, quartered 4 carrots, sliced 1/2 pound fresh pumpkin, cut in 1-inch pieces (or substitute zucchini) Water 1/2 teaspoon cayene pepper or 3 or 4 fresh hot green peppers cut in half 1 cup cooked chick peas Salt and pepper to taste

The fish may be either a combination or any of the following: 2 to 2 1/2 pounds fish filets of rockfish, sea bass, snapper, cod or haddock. Or 1 whole 4-pound fish, with head and tail, sliced in 2-inch slices, or 3 pounds of small whole fish (about 1/2 to 3/4 pound each) can be used.

Heat oil and fry onions and garlic until golden brown. Add tomato paste and tomatoes. Let simmer until blended. Add 1 cup of water and bring to a boil. Reduce heat. Add potatoes, carrots and pumpkin. Cover with water and cook until vegetables are tender.

Add cayenne or hot peppers, chick peas, salt and pepper. Simmer for about 20 minutes. Five minutes before serving time add fish to the simmering soup.

To serve place the grain on one platter. The boullion should go in a tureen or large bowl with a ladle. The fish cakes may be placed on another platter and garnished with fresh parsley. The fish should be carefully removed from the soup and placed on a large serving platter with the vegetables around it or all on one side.

Each individual places some of the couscous on their plate and adds the desired amount of soup. The fish cakes are added, and may be eaten as a separate course. The fish and vegetables comes next.