The ethereal hot souffle long has been considered a hallmark of haute cuisine . Many cooks, however, have never attempted to make one, believing that a dish so impressive must be difficult to prepare. Understanding how a souffle is made can remove a lot of its mystique. In fact, you can enjoy souffles even more once you know how to prepare them without fear of failure.

The literal translation of the word souffle is "blown up" of "inflated." This effect is achieved by the addition of whipped egg whites. Souffles can be sweet or savory, but egg whites are always the essential ingredient that gives them their characteristic texture and appearance. "Bavarians and mousses are sometimes called cold souffles, and they, too contain whipped eggs whites. But the classic souffle is hot.)

In general, a souffle starts with a roux, composed of melted butter and flour, to which milk or another liquid is added. This mixture is thickened with beaten eggyolks. Then the primary flavoring ingredient, such as grated cheese, melted chocolate or pureed fruit, is added.

The final step before baking is folding in whipped egg whites. To whip them successfully, there are few basic rules to follow. When you are separating your eggs, special care must be taken that no bits of yolk or shell get into the whites. They should be at room temperature. Make sure that your bowl and beaters contain no residue of grease. A pinch of cream of tartar will help incresae the volume of machine-beaten egg whites.

The whites are folded gently into the flavored cream sauce until no clumps of white remain. (Do not overfold or beat as air beaten into the whites will escape. You can use more egg whites than called for in most recipes.The resulting souffle will be lighter and puffier.

A souffle should be baked in a souffle dish or a similar flat-bottomed, straight-sided casserole. If the sides are not at right angles to the bottom, the souffle will not rise as high. The dish should be well buttered and for a nice crust, sprinkle the dish lightly with grated cheese or sugar, depending on the recipe.

There is no truth to the popularity held belief that you must tiptoe around your kitchen while the souffle is baking to prevent it from falling. Observe it during cooking and if it is rising unevenly, open the oven door and adjust its position. The souffle should be served as soon as it is removed from the oven; it will collapse shortly if left standing.

When entertaining, you can assemble a main-dish souffle just after guests arrive and bake it while you are serving drinks and hors d'oeuvre. Give notice to move to table about 10 minutes before it is ready.

If serving a dessert souffle to company, do all the steps in advance except whipping and incorporating the egg whites. This can be done while you are preparing after-dinner coffee, and your guests can linger over coffee while the souffle is baking.

Once the basic techniques of souffle-making are mastered, you can vary them with different flavoring ingredients. A cheese souffle, for example, can be enhanced by the addition of chopped spinach, broccoli, mushrooms or crabmeat. But be careful not to overload a souffle with too many ingredients.

Here are two basic souffle recipes with suggested variations to try. CHEESE SOUFFLES (4 servings)

Serve as a main dish for a luncheon or light supper. Round it out with French bread, tossed salad and your favorite wine. 7 tablespoons butter 6 tablespoons flour 1 teaspoon salt Dash of caynenne pepper and paprika 1/4 teaspoon dry mustard 1 1/2 cups milk 1 1/2 cups (6 ounces) Cheddar or Swiss cheese, grated 7 egg yolks 7 to 10 egg whites, at room temperature 1/2 teaspoon cream of tartar

With 1 tablespoon of hte butter, grease the sides and bottom of a 2-quart souffle dish. If desired, dust insides of dish with fresh bread crumbs or additional grated cheese. In a small saucepan, over medium heat, melt remaining butter; blend in flour and seasonings, stirring until smooth. Meanwhile, gently heat milk in another saucepan until hot to the touch. Add milk to flour mixture all at once, stiring brishly with a wire whisk. Continue cooking, stirring constantly, until mixture is thickened and smooth. Add cheese, and stir until melted. Remove from heat, and let cool a few minutes.

Preheat oven to 350 degrees. With electric mixer at medium speed, beat egg yolks until thick and lemon-colored - about 3 minutes. Sitr a little of the cheese mixture into egg yolks, and then gradually stir this mixture into cheese sauce, blending well. Transfer mixture to a large bowl.

Wash and dry beaters thoroughly. Whip egg whites and cream of tartar in another large bowl until stiff but not dry. Using a rubber spatula, carefully fold egg whites into cheese mixture until thoroughly incorporated. Pour mixture into prepared souffle dish, and bake 50 minutes, or until puffed and brown. Serve at once. VARIATIONS

Spinach Souffle: Cook one 10-ounce package of frozen chopped spinach according to package directions; drain very well. Make cream sauce as above, but decrease amount of milk to 1 cup. Add drained spinach along with cheese to cream sauce, and proceed as above.

Mushroom Souffle: Finely chop 1/4 pound of mushrooms, and saute in 2 tablespoons of butter until all liquid has evaporated. Add to cream sauce along with cheese, and proceed as above.

Crabmeat Souffle: Use 1 cup of flaked crabmeat, and decrease grated cheese to 1/2 cup. Add both to cream sauce, and proceed as above. CHOCOLATE SOUFFLE (6 servings) 3 tablespoons butter 1/2 cup plus 1 tablespoons sugar 2 squares unsweetened chocolate (2 ounces) 2 tablespoons strong brewed coffee 2 tablespoons flour 3/4 cup milk Pinch of salt 1 teaspoon rum (or vanilla) 3 egg yolks 5 egg whites, at room temperature Pinch of cream of tartar

With 1 tablespoon of the butter, grease sides and bottom of a 2-quart souffle dish; sprinkle with 1 tablespoon of the sugar. Place chocolate, coffee and 1/3 cup of the sugar in top part of double boiler. Cook over hot water until chocolate has melted; set aside.

In small saucepan, melt remaining butter over medium heat; blend in flour until smooth. Meanwhile, gently heat milk in another saucepan until hot to the touch, and add to flour mixture all at once, stirring briskly with a wire whisk. Add salt, and continue cooking, stirring constantly, until mixture is thickened and smooth. Stir in melted chocolate mixture and rum. Remove from heat, and set aside to cool.

Preheat oven to 375 degrees. In small bowl, with electric mixer at medium speed, beat egg yolks until thick and lemon-colored - about 3 minutes. Add to cooled cholocate mixture, and transfer to a large bowl. IN another large bowl, beat egg whites and cream of tartar at high speed until soft peaks form. Gradually add remaining sugar, and continue beating until stiff peaks form. Fold into chocolate mixture with rubber spatula until thoroughly incorporated. Transfer to prepared souffle dish, and bake 40 minutes, or until puffed and dark brown. Serve at once with sweetened whipped cream, if desired. VARIATIONS

Chocolate-Orange Souffle: Substitute 2 tablespoons of orange liqueur for the coffee; use vanilla instead of rum; proceed as above.

Cherry Souffle: Omit chocolate and coffee. Prepare cream sauce as above. When adding beaten egg yolks to cream sauce, also add 1/2 cup of the sugar, 1 tablespoons of cherry liqueur, 1 teaspoon of cinnamon, 1 teaspoon of vanilla, and 1/2 cup sliced pitted black cherries. Proceed as above.