Weathermen keep talking about the "cold front" that came our way last weekend. It's a perfect example of relativity: since when is 85 or 90 degrees considered cold? But Washington probably hasn't seen anything yet. The "dog days" of August are still ahead."

Maybe the best way to adjust to the heat and humidity of this city built on a swamp is to change your lifestyle by turning night into day: shop for groceries at 8 or 9 p.m.; adopt the Spanish custom of eating a light supper late in the evening. The Spanish take long siestas at noon, a habit Washington might do well to emualte in the summer. (Can't you see the government office buildings clearing out from 12 to 3?) Then they have a snack when they get home from work and eat dinner at 10 or so. If you want to try that, keep the meal light. It isn't a good idea to go to bed on a stomach full of heavy food.

And think about the relative pleasure of lugging heavy grocery bags in the cool of the evening instead of the heat of the midday sun. A few supermarkets stay open for 24 hours so you can shop at 2 a.m. if you are so inclined.

You might also want to cook at night for the next day, or do so early in the morning when the temperature are at their lowest. That way the kitchen will be cooled down when you are serving food and washing dishes.

No matter the time of day, foods during torrid weather should be light. Not only are they more appealing psychologically, but they contain fewer calories. During heat waves most people expend less energy anyway. Fruit and vegetable salads, cold soups, low-fat cheese, hard-cooked eggs satisfy hunger and don't offer a calorie overload.

Drink lots of liquids, preferably water, fruit or vegetable juices or tea with lots of ice. Keep a pitcher of brewed tea in the kitchen so that you don't have to stop to make it and then cool it down before adding ice. (Don't put the tea in the refrigerator because it become cloudy.)

Mary Goodwin, a nutritionist with the Montgomery County Health Department, recommends keeping a container of water with ice cubes in the refrigerator because she explains, children like rituals. "That's more special than just turning on the tap," she said. She also suggested putting a slice of lemon in a glass of water to make it more refreshing. "You may also want to find things to keep the children busy," Goodwin said, and she mentioned having them make various cold drinks with fruits and milk or yogurt or making yogurtsicles, a nutritious form of popsicle.

For some people the loss the salt because of excessive perspiring can be a problem. Unless you are on a special diet, the best way to replace the salt your body has lost is by adding a little more than normal to your foods.

For the cook in the family, the less that has to heated on the stove the better. The oven probably should be abandoned during the hottest weather. Even if you have air-conditioning, oven heat warms up the surrounding air and can make it pretty uncomfortable. It's better to cook on top of the stove or use a toaster-oven or other small appliances that do not give off the kind of heat a stove does.

If all else fails and you're still hot, you might toss around the idea of taking your meals sitting in a bathtub filled with water.

The recipes that follow call for a minimum amount of cooking - all in advance - or no cooking at all. The first is from Pedro Sanjuan, one of the city's most electric cooks. GAZPACHO ALA SANJUAN (8 servings) 2/4 cup olive oil 4 cloves garlic, crushed 1/2 medium onion lightly crushed against the side of the bowl 4 or 5 snips fresh parsley crushed against the side of the bowl 1 1/2 teaspoons salt 1/2 cup vinegar 1 cup red burgundy (about) 2 ripe tomatoes 1 can (16 ounces) whole tomatoes 1 can (24 ounces) tomato juice 1 large, ripe avocado Chives for garnish

In a mixing bowl combine oil, garlic, onion, parsley, salt, vinegar and some of the wine. Pour half this mixture into the blender. Add half the remaining ingredients. Blend until mixture is thoroughly pureed. Pour into another bowl and repeat operation with remaining ingredients. Combine with first batch. Strain mixture through fine wire strainer. Press any residue left in strainer against sides with spoon until only wet pulp remains in strainer, discard residue.

You may choose to use less wine, so do not add all of it to soup. After mixture are blended, add more wine to taste. Adjust salt if necessary. Chill thoroughly. Serve with chopped chives for garnish.

HUMMUS (Middle Eastern chick pea puree) (4 servings) 1/3 cup sesame oil 1/2 cup lemon juice 1 large clove garlic, chopped 1/2 teaspoon salt 1 cup cooked chick peas 1 tablespoon chopped parsley

Combine oil, juice, garlic and salt in blender and blend until smooth. Through opening in cover add a few chick peas at time and continue blending until mixture is smooth. If it is too thick, thin with a little water. Chill and serve sprinkled with parsley with pita bread. BULGUR SALAD (8 servings) 1 cup bulgur 2 cups cold water 1 teaspoon salt 1/2 cup oil and vinegar dressing 2 tablespoons diced green pepper 1/4 cup chopped chives or green onion 1/2 cup diced celery 8 pimiento-stuffed olives, sliced 1 1/2 pounds cooked, creamed shrimp, halved or 3 (6 1/2-or 7-ounce) cans tuna, rinsed and drained 12 cherry tomatoes 1/4 cup mayonnaise of half yogurt and half mayonnaise Crisp salad greens

Combine the bulgur, water and salt and bring to boil. Reduce heat; cover tightly and simmer 15 minutes. Drain. Pour oil and vinegar dressing over hot bulgur. Chill at least an hour or overnight. Add remaining ingredients except greens to bulgur and mix well. Chill thoroughly. Serve on the salad greens. CHICK PEA SALAD (4 to 6 servings) 2 cans (1 pound, 4 ources) chick peas, drained 1 medium onion, chopped 1/2 cup sliced sweet gherkins 1/2 cup sweet pickle liquid Salt and freshly ground black pepper 3 tablespoons wine vinegar 2 whole pimientos, cut up

Combine ingredients and mix lightly. Chill overnight. Garnish with additional pimiento, if desired. EGG AND AVOCADO SALAD (4 servings) 4 ounces crumbled blue cheese 2 ripe avocados, cut in strips and dipped in lemon juice 1 large head leaf lettuce, broken into pieces 4 hard-cooked eggs, sliced 1 cup garlic-flavored oil and vinegar dressing

Gently mix together the cheese, avocados, lettuce and eggs. Then loss with dressing and serve. SARDINE AND FETA SALAD (4 servings) 1 head leaf lettuce, broken into pieces 1 cup chopped celery 2 cucumbers, peeled and chopped 2 small onions, thinly sliced 4 medium tomatoes, sliced 1 green pepper, chopped 10 black olives, sliced 1/2 pound feta cheese, crumbled Juice of 4 lemons 2/3 cup olive oil 1 can sardines, drained 2 teaspoon oregano

Gently mix together the vegetables and feta cheese. Chill. Combine the lemon juice and olive oil. When ready to serve, toss the salad with the dressing. Garnish with sardines and sprinkle with oregano. BLUEBERRY SOUP (Makes about 5 cups) 1 pint fresh blueberries, washed, stems removed Peel of one lemon 4 cups water

1/2 cup dry vermouth 6 to 8 tablespoons sugar 3 whole cloves 1 stick cinnamon 1/4 cup fresh orange juice 1 cup sour cream

Combined all ingredients except sour cream in pot and cook over medium heat until frust burst and softens. Remove lemon peel, cloves and cinnamon and puree the liquid, about a cup at a time, in blender. Chill thoroughly, for several hours or overnight, Serve, topped with sour cream. STUFFED EGGES (12 halves) 6 eggs, hard-cooked 1 teaspoon Dijon mustard 1 tablespoon minced onion 1/2 clove minced garlic Dash cayenne pepper 2 tablespoons minced celery 3 tablespoons mayonnaise 1/2 teaspoon lemon juice Salt and freshly ground black pepper to taste

Shell eggs, cut in half and remove yolks. Mash yolks with remaining ingredients and fill whites with the mixture. Garnish with paprika. COLD CUCUMBER SOUP (6 to 8 servings) 4 tablesspoons butter 1/2 cup green onion 3 cups peeled, chopped cucumber 3/4 cup diced potatoes 4 cups chickens broth 1 cup watercress leaves Salt and pepper to taste Dash hot pepper sauce 2 cups sour cream or yogurt Minced chives

Melt butter in skillet. Saute green onions in butter until they are wilted. Add the cucumbers, potatoes and broth and simmer 15 minuted. During last five minutes add watercress leaves. Season to taste with salt and pepper. Puree in blender, chill. When cooled add hot pepper sauce and sour cream. Chill again for at least two hours or longer. To serve, garnish with chives. SHERLEY KOTEEN'S VICHYSQUASH (4 servings) 1 zucchini, the size of a large cucumber 2 tablespoons snipped fresh dill or 2 teaspoons dried dill 10 sprigs watercress, including stems 3 ounces cream cheese 1 cup low-fat milk 1 tablespoon olive oil 3 tablespoons finely chopped onion 1 small clove garlic, chopped 3/4 to 1 teaspoon curry power 2 teaspoons lemon juice 1/4 teaspoon ginger Salt and freshly ground black pepper to taste

Combine all ingredients in blender and blend until mixture is smooth. Chill thoroughly and serve ice cold garnished with sprigs of watercress.

The following two recipes are from "Love At First Bite," by Jane Cooper, (Alfred Knopf, $3.50) a cookbook for children that has for more nutritious recipes in it than most kids' cookbooks. YOGOFROOSICLE

Combine plain yogurt with defrosted frozen juice concentrate and whatever proportions desired, beginning with equal amounts. If you want it sweeter, add more juice. For every 2 cups of yogurt-juice mixture you can add one of the following if you like: 1 small can crushed pineapple; 1/2 cup apple juice; 1 cup mashed bananas; 1 tablespoon grated orange or lemon peel; 1 cup crushed berries; 1 cup peeled, chopped peaches.

Blend ingredients in blender and either spoon into plastic molds or paper cups. Place in freezer . IF using paper cups, let mixture harden until it is thick and slushy. Then insert a popsicle stick in center of each cup. Return to freezer and freeze until popsicles are hard. To eat from paper cup, peel off paper. Hold plastic mold under hot water to loosen. BLACK AND BLUE BERRIES (1 or 2 servings) 1 cup black or blueberries 1 cup soda water 2 tablespoons honey or sugar 1 teaspoon lemon juice 3 or 4 pieces of ice

Place berries, soda, honey and juice in blender and mix at medium speed until well blended.While blender is still on, remove center of the cover and drop in ice cubs; blend until completely crushed. Variation: 2 cups cold milk, 1/2 teaspoon almond extract, 4 teaspoons honey or maple syrup, 3 or 4 ice cubes.