THE HOTTEST summer day can be cooled by something as simple as the sight of seashells on a windowsill, garden tomatoes, freshly washed and dewy, or a frosty cup of chilled soup, ready for tasting. Chilled soup is a perfect illustration of the importance of the presentation, the "imagery" of food. It can be served anytime, of course, but cold soup is most effective and supportive when served attractively, with subtle flavor, gentle fragrance and cool essence, which contrasts so bracingly with hot weather. Well-chilled soup in a chilled dish definitely has a soothing effect when the temperature is rising. a

Chilled soup has many advantages. It can be prepared early in the day, refrigerated, and can come to the rescue as a light summer lunch or first course at dinner. As a change of pace from the standard breakfast fare of cereal or eggs, try tangy, chilled fruit soup. Chilled soups are easy to make, usually requiring little more than combining ingredients, or a brief whirling in a blender. They are fertile ground for experimentation and a good way to recycle leftovers. Put well-chilled soup in an insulated thermos and it is ready to go on any picnic or boating party.

Here are a few fundamentals for making quick and easy chilled soups: keep in mind that any fruit juice (fresh, frozen or canned) can be used as the liquid, or base for a fruit soup. Just add peeled and chopped fruits to taste, or put the whole works in the blender for a smooth soup. Tomato juice and any combination juices (tomato/beef, tomato/vegetable) can be the base for a vegetable soup. These can be enriched with raw, fresh vegetables pureed in the blender, and vegetable soup base can be made entirely from fresh vegetables whirled in the blender. Experimentation will show what textures and thicknesses are most appetizing. Ice water can be used as a thinner, and milk, buttermilk and yogurt are other liquids to consider.

Remember the importance of presenting chilled soup attractively to gain the benefit of eye appeal. Choose serving dishes that contrast nicely with the color of the soup, garnish with parsley, cress, chives, small whole vegetables, fruits, berries or whatever is appropriate. And chill the serving dishes well before serving the soup to assure cold soup from the first sip to the last. COLD CELERY SOUP (8 servings) 4-1/2 cups sliced celery 2 cups milk 1-1/4 teaspoons salt

Put ingredients in blender and mix thoroughly. Strain through fine strainer, being sure to extract all liquid. Refrigerate. Serve this delicate soup within three hours of refrigerating. Number of servings depends on water content of celery and how much liquid is extracted. Garnish with small, thin celery slices or cress. ICED AVOCADO-CUCUMBER SOUP (3 servings) 1/2 ripe avocado, peeled and cubed 1 cucumber, peeled, seeded, cubed 2 scallions, sliced, including some of green part 1 cup chicken stock 1 cup sour cream 2 tablespoons lime juice Salt and Pepper to taste Chopped chives for garnish

Place all ingredients except chives in blender and liquefy. Chill mixture at least 8 hours. Serve topped with chopped chives. CHILLED STRAWBERRY SOUP (4 servings) 2 pint boxes fresh strawberries, washed and hulled 1 cup orange juice 1-1/4 teaspoons instant tapioca 1/8 teaspoon ground allspice 1/8teaspoon cinnamon 1/2 cup sugar 1 teaspoon grated lemon peel. 1 tablespoon lemon juice (or more) 1 cup buttermilk Paper-thin lemon slices

Set aside 6 strawberries. Puree remaining berries in blender. Strain into 4-quart saucepan and add orange juice. In a small bowl, mix tapioca with 4 tablespoons pureed strawberry mixture. Add to saucepan with allspice and cinnamon. Heat, stirring constantly until mixture comes to boil. Cook 1 minute or until thickened. Remove from heat. Pour soup into large bowl. Add sugar, lemon peel, lemon juice and buttermilk and blend well. Slice reserved strawberries and fold into soup. Cover and chill at least 8 hours. Serve in well-chilled melon halves. Float thin lemon slices on each serving. CHILLED SHRIMP SOUP (6 servings) 1/2 pound shrimp, cooked peeled and coarsely chopped 1/2 finely diced cucumber 1 tablespoon minced fresh dill 1 tablespoon prepared mustard 1 teaspoon salt 1 teaspoon sugar 1 quart buttermilk

Mix together the shrimp, cucumber, and the seasonings. Stir in the buttermilk and chill thoroughly. Serve in chilled soup plates. PEACH SOUP (4 servings) Very ripe peaches, enough to fill 2 cups when pureed 2 tablespoons lemon juice 2 tablespoons sugar, or to taste 1 bottle dry white wine 1 small bay leaf Pinch of salt Mint leaves for garnish

Peel and puree peaches in blender. Put the 2 cups puree in a deep bowl, sprinkle with lemon juice and sugar. Cover and let stand 20 minutes. In the meantime, bring the wine, salt, and bay leaf slowly to a boil. Simmer for 1 minute or so, then strain. Leave it until cold. Then stir the wine into the puree. Serve. Garnish with mint leaves. COLD PUREE OF CARROT SOUP (4 servings) 4 large carrots, peeled and quartered 1 large onion, quartered 2 cups chicken broth Salt and pepper to taste 1 tablespoon sherry or marsala wine 1 cup milk Chopped chives or parsley for garnish

Simmer carrots and onion in broth until carrots are tender. Place in blender with salt, pepper, wine and milk. Blend until smooth. Chill several hours or overnight. Garnish with chopped chives or parsley. CHILLED VEGETABLE SOUP (makes about 2-1/2 quarts)

This soup is best served no sooner than a day after it is made. Will keep for a week in the refrigerator, and freezes well. 1 pound cucumbers 2-1/2 pounds tomatoes 1/2 pound green peppers 1/2 pound red onions 3/4 teaspoon chopped hot peppers 2garlic cloves 5 tablespoons red wine vinegar 1 cup oil 1-1/4 tablespoons salt 2-1/2 cups water

Peel cucumbers, remove hard core from tomatoes, remove seeds and stems from peppers. Peel onion. Cut all vegetables into large bite-size pieces and put in large bowl. Add vinegar, oil, salt, hot pepper, garlic and water. Stir. Put in blender by batches and mix until smooth. Refrigerate. wThis soup is best served very cold.