It's too hot to cook. The air is thick enough to knock you over. Isn't it lucky that something thrives on this weather - namely fruit; peaches, plums, melons, cherries and berries. Combine them with year-round standbys like apples, bananas and nuts and dinner is served.

When ripe and sweet, the fruit can be served sliced and completely naked, as long as lemon is added to those that discolor quickly - peaches, apples, bananas. For a light dinner, mix together several fruits and serve with a generous dollop of ricotta cheese, along with hot biscuits, and a dry white wine. Or with the fruit and wine, try some French bread and Swiss cheese or Danish havarti.

Dressing a fruit salad can be quick and simple, too. A small can of unsweetened pineapple chunks, juice and all, will do when topped off with some walnuts. Or add some toasted sesame seeds, and you could almost be in California.

A handy base for another dressing is home-made mayonnaise, prepared with lemon juice rather than vinegar. Light and fluffy, it bears only a slight resemblance to its namesake on the grocery store shelf. For the sweet-toothed, it can be flavored with fruit juice; for those after something heartier, with blue cheese or avocado.

Main course, side dish, appetizer, dessert - fruits is comfortable any place in the meal. Soak strawberries and peaches in wine, they're an appetizer; soak them in brandy, and they're dessert. Served with a choice of dressings, a fruit bowl can suit a variety of tastes at a luncheon. And to top off a meal, summer offers fresh berries and whipped cream.

Some samples follow: FRUIT WITH YOGURT TOPPING (serves 4) 3 peaches, sliced 1 cup cherries, halved and pitted 1 cup blue berries 1 tablespoon lemon juice 1/2 pint to 1 pint vanilla-flavored yogurt 1/4 cup honey 1/4 cup sunflower seeds 1/2 cup raisins

Squeeze lemon juice on the peaches to prevent discoloration. Mix fruit together and divided into individual servings. Top each serving with spoonfuls of vanilla yogurt, then dribble honey over the yogurt. Garnish with raisins and sunflower seeds, or with any of the following: shredded coconut; chopped fresh mint; walnuts, almonds, peanuts, or pecans; silvered candied ginger. PLUM SALAD (4 servings) 4 plums, sliced 1 cup green grapes 2 tablespoons sliced toasted almonds Lettuce Lime French Dressing

Arrange plum slices in a row on a bed of lettuce. Halve the grapes, remove the seeds, and place next to the plums. Sprinkle toasted almonds on top and serve with Lime French dressing. LIME FRENCH DRESSING (About 3/4 cups) 1/4 cup lime juice (4 small limes) 1 teaspoon sugar 1/4 teaspoon sugar 1/4 teaspoon salt 1/4 teaspoon dry mustard 1/4 teaspoon paprika 1/2 cup vegetables oil

Combined all ingredients in a jar and shake well. BLENDER MAYONNAISE (Makes 1 1/4 cups) 1 egg 2 tablespoons lemon juice 1/4 teaspoon dry mustard 1/2 teaspoon salt 1 cup vegetable oil

Break egg into blender jar, add lemon juice, salt and mustard, and blend at high speed until throughly mixed. Removed the top of the jar and while the blender is running at high speed, gradually add the oil in a very slow, steady stream.

Use homemade mayonnaise to make the following dressings.

Honey-Lemon Mayonnaise: To 1 cup mayonnaise, add 1/4 cup honey, 1/4 cup lemon juice, 1 teaspoon grated lemon rind, and 1/2 teaspoon paprika.

Serve with a salad of sliced strawberries and plums, orange sections, and avocado.

Avocado Sauce: Put the meat of a ripe avocado through a sieve. Add to it 1/2 cup mayonnaise, 1/2 cup sour cream, 2 tablespoons lemon juice, 1/4 teaspoon salt and few drops of hot pepper sauce. Makes about 2 cups.

Serve with a salad of fresh pineapple, orange and grapefruit sections, and lettuce.

Pineapple Mayonnaise: Mix together 1/2 cup mayonnaise, 1/2 cup pineapple juice, 1 tablespoon honey, and 2 tablespoons lemon juice. Fold in 1/2 cup whipped cream. Makes 1 1/2 cups.

Serve with tropical salad. TROPICAL SALAD (6 servings) 1 pineapple 2 large oranges 2 papayas Lettuce

The three fruits are sliced in rings, then placed in alternate layers on a bed of lettuce.

To prepare pineapple, cut away the leafy top and the hard outside skin. Slice the flesh into circles and cut out the though inside core.

Pare the papaya and slice it into rings. Carefully remove the black seeds in the center, leaving a star-shaped hole.

Peel the oranges, slice in circles and remove the seeds.

Arrange slices in alternative layers on the lettuce on individual dishes and serve with pineapple mayonnaise. FRESH FRUIT COMPOTE (Serves 8 to 10) 1/2 cantaloupe, sliced in crescents 1 cup strawberries, halved $1 cup sliced peaches or nectarines 1 cup sliced apples 1 cup blueberries 2 bananas, sliced 2 tablespoons lemon juice

Arrange strips of cantaloupe around the inside of a large glass bowl. Toss the rest of the fruit with the lemon and add to the bowl, garnishing with some of the blueberries.

Serve with currant-cream cheese dressing. CURRANT CREAM CHEESE DRESSING (About 1 1/4 cups) 1 package (3 ounces) cream cheese 1/4 cup currant jelly 2 tablespoons lemon juice 1/2 cup heavy cream, whipped

Soften the cream cheese, then mix in currant jelly and lemon juice until smooth.Fold in whipped cream and chill