Giving elegance to the common cucumber

''A cucumber should be well sliced, and dressed with pepper and vinegar,'' said Dr. Johnson, ''and then thrown out, as good for nothing.'' Samuel Johnson, who lived in a cool and moist climate, obviously didn't realize that for those of us who live in a hot, dry climate, the cucumber has one great virtue - its high water content. Not for nothing do we say ''cool as a cucumber.''

For nearly 10,000 years mankind has grown the cucumber in hot climates, first in the Far East, then gradually eastward over the millenniums. The Indians, Egyptians, Greeks, and Romans have all appreciated it in turn.

It spread slowly in northern Europe, but the American Indians of the Southwest took to it at once.

During the last century, according to food writer Waverly Root, the cucumber has been widely cultivated in the Sahara. Had Dr. Johnson tasted it there, perhaps he would have had kinder words for it.

Here are some recipes to help keep you cool as a cucumber during the hot summer days. Cucumber and Leek Soup 1 pound cucumbers, peeled and seeded 1 pound leeks, green tops trimmed 3 tablespoons butter 1 1/2 quarts chicken stock 2 tablespoons chopped fresh chervil or parsley 2 tablespoons chopped fresh chives Salt and pepper to taste

Quarter leeks lengthwise almost to roots and wash thoroughly. Coarsely chop leeks. Peel cucumbers, halve lengthwise, scoop out and discard seeds, then cut in slices. Melt butter in large pot and saute vegetables for 15 minutes, stirring often, until soft but not brown. Add chicken stock, cover, and simmer 30 minutes.

Cool, then puree in blender or food processor. Stir in chopped herbs, then salt and pepper to taste. Serve well chilled, garnished with a dollop of sour cream and a sprig of fresh herbs. Serves 6.

This soup is a lighter alternative to vichyssoise and may be enriched with a little cream. Cucumber Salmon Cups 2 cucumbers, preferably thin ones 1/2 cup smoked salmon pieces, chopped 2 scallions, green tops included, finely chopped 1/2 cup sour cream Capers

Peel cucumbers and cut crosswise into 3/4-inch sections, making about 16 pieces in all. Leaving a layer at bottom, scoop out seeds with melon ball cutter , to form cups. Drop into boiling salted water 2 minutes to blanch. Drain well, upside down, and set aside.

Mix together salmon, scallions, and sour cream. Put a spoonful of the mixture into each cup and top with a caper. Chill well before serving.

This is an excellent garnish for broiled or poached fish or summertime salads. Made with small cucumbers, they are good hors d'oeuvres. Cucumber Mousse 2 large cucumbers, peeled and seeded 1 tablespoon unflavored gelatin 1/4 cup lemon juice 3 tablespoons horseradish, or to taste 1/2 teaspoon salt 1/4 teaspoon white pepper 1 cup heavy cream 1 egg white

Puree cucumber flesh in a food processor, blender, or food mill, to measure about 2 cups. Soften gelatin in lemon juice about 5 minutes, then dissolve over gentle heat, stirring constantly. Mix horseradish, salt, and pepper into cucumber puree.

Whip cream until it makes soft peaks, then whip egg white in another bowl with a clean whip. Quickly fold whipped cream into cucumber puree, then add egg white. Pour into a 4- or 5-cup mold, cover with plastic wrap, and refrigerate until set.

To unmold, dip mold into hot water, place serving plate on top, and invert. Decorate with watercress, then slices of unpeeled cucumber, curls of smoked salmon, or whatever you like. Serves 6. Shrimp and Cucumber Salad 3 cups tiny shrimps, cooked 1 cucumber, peeled, seeded, and diced 1/2 cup mayonnaise, preferably homemade 1 scallion, green top included, chopped 2 tablespoons chopped fresh dill 2 tablespoons lemon juice Salt and pepper to taste

Mix together all ingredients. Serve well chilled on crisp lettuce leaves, garnished with a large shrimp. Or for each serving stuff a whole green pepper with the salad and top with a sprig of fresh dill. Serves 6.

Sauteed Cucumbers With Mint

2 large cucumbers

Salt

2 tablespoons sweet butter

2 scallions, green tops included, chopped

4 tablespoons chopped fresh mint

4 tablespoons sour cream or yogurt, optional

Salt and pepper to taste

Slice cumbers, place in a colander, salt generously, and leave at least 30 minutes to draw out liquid, then rinse and dry.

Melt butter in large frying pan and saute scallions until soft. Add cucumber slices and cook about 6 minutes, stirring often, without browning.

Add sour cream, mint, and salt and pepper. Stir well to combine. Serves 4.