MANY overweight people don't gorge. They're fat -- and stay that way--because they regularly eat a little more than they need. Those extra pounds sneak up, seemingly out of thin air. In theory, if you consume just 117 more calories than you need daily, you'll gain a pound each month, since there are 3,500 calories in a pound of fat. Fortunately, by cutting 117 calories daily--or expending 117 calories in additional activity--you can lose those extra pounds.

One way to easily cut 117 calories out of your daily fare is to use low-calorie substitutes in lieu of mayonnaise, sour cream, traditional vinaigrette, or other salad dressings. Bottled dressings are particularly expensive, calorically speaking. Kraft French has 65 calories per tablespoon. Wish-Bone Italian has 75. Hellman's mayonnaise has 97 calories per tablespoon, although homemade versions aren't usually any less.

By substituting a tasty low-calorie dressing for three or four tablespoons of your regular choice, you can lose--or avoid gaining--a pound a month. It's a small, economical sacrifice when compared to more drastic measures necessary should those pounds add up. But remember, even with low-calorie salad dressings, it isn't always what kind you use, but how much. LOW-CALORIE VINAIGRETTE (Makes 1 cup) 1/4 cup vegetable oil 1/4 cup wine vinegar 1/4 cup lemon juice 1/4 cup tomato juice 1 clove garlic, minced 1/8 teaspoon ground pepper 1/4 teaspoon crushed thyme 1/4 teaspoon salt 2 teaspoons chopped parsley

Mix ingredients well. Store in refrigerator. About 30 calories per tablespoon. THOUSAND ISLAND DRESSING (Makes 1 1/4 cups) 1/4 cup chili sauce 2 tablespoons finely chopped onion 1 teaspoon vinegar 1 teaspoon prepared mustard 1/2 teaspoon salt 1 cup plain yogurt

Blend first five ingredients; stir in yogurt. Store in refrigerator. About 10 calories per tablespoon. HERB CHEESE DRESSING (Makes about 2 cups) 1 cup cottage cheese 2 tablespoons wine vinegar 1/4 teaspoon oregano 1/4 teaspoon basil 1/4 teaspoon thyme Dash garlic powder 1 teaspoon grated onion 1 cup plain yogurt

Beat all ingredients together well. Store in the refrigerator. About 11 calories per tablespoon. OTHER YOGURT COMBINATIONS

Greek: Combine 1 cup plain yogurt with 3 tablespoons lemon juice and 1 teaspoon garlic powder or 2 cloves minced, fresh garlic. About 9 calories per tablespoon.

Dressing for cole slaw: Combine 2 tablespoons chopped parsley, 1 teaspoon dill weed, 2 minced garlic cloves or 1 teaspoon garlic powder and 1 cup plain yogurt. About 9 calories per tablespoon.

Dressing for fruit: Combine 1 cup plain yogurt and 2 tablespoons orange juice concentrate. About 9 calories per tablespoon. LOW-CALORIE COOKED DRESSING (Makes 1 cup) 1/2 cup wine vinegar 3 egg yolks 1/2 teaspoon prepared mustard or 1 teaspoon dried tarragon 1/8 teaspoon salt 1/4 teaspoon cayenne pepper

Heat wine vinegar to boiling. Beat egg yolks over hot water in a double boiler. Slowly add vinegar to yolks, stirring constantly, until thick and smooth. Season to taste with mustard or tarragon, salt and red pepper. The mustard version is good on hot or cold potato salad. Choose the tarragon for mock be'arnaise sauce. About 17 calories per tablespoon. HORSERADISH DRESSING (Makes 3/4 cup) 1/2 cup buttermilk 1 tablespoon vegetable oil 1 tablespoon vinegar 1/2 teaspoon salt Dash pepper 1 teaspoon prepared horseradish 1/2 teaspoon dried tarragon

Combine all ingredients and mix well. Store in refrigerator. An outstanding dressing for spinach salads. About 15 calories per tablespoon.