When your parents offer you a special treat, do you rush off to the nearest fast-food restaurant to feast on hamburgers, fries and soda pop? A lot of kids do. Many people make fast-food meals a part of their daily diet. Americans spend $20 billion on fast food every year. That's a lot of french fries.

The food you get at the fast-food place around the corner may be convenient and fun -- but most of it is not good for you. Burgers and fries and the other selections on the fast-food menu tend to be high in calories and fat, and low in nutrients. The Center for Science in the Public Interest, an organization that looks at this sort of thing, says that some fast-food restaurants cook their food in beef fat or other kinds of shortening that change even low-fat foods like chicken, fish, and potatoes into fatty snacks.

You need nutrients for health and growth. You need calories for energy -- but too many calories can make you overweight. You even need fat -- but in very, very small amounts. French fries, a quarter-pound hamburger and a milk shake may contain as much as 1,000 calories -- and about one third of those calories come from fat, not nutrients. That's too much.

Fast foods don't need to be completely off limits. But you should use common sense about eating them. Don't make eating fast food a way of life. Here are some suggestions to help you eat well in a fast-food restaurant:

*Limit eating fast foods to a couple of times a week at most. Order hamburgers without toppings like pickles or ketchup, which contain loads of salt. Use tomatoes, onions, and lettuce instead.

*Order the smallest size of hamburger.

*Remove the skin from fried chicken. With skin, fried chicken is about the fattiest food you can order at a fast-food restaurant.

*Skip the french fries. Eat a baked potato instead; many fast food places serve them now.

*Use the salad bar, but avoid foods with mayonnaise, which contains salt, fat and a substance called cholesterol that can build up in your blood and cause trouble for your heart later on. Nutrition experts and children's doctors encourage kids to get into the habit of eating healthier foods than they can get at a fast-food restaurant. Doctors are concerned because many American kids are overweight. The American Academy of Pediatrics reports that obesity, -- being dangerously overweight -- is the most serious nutritional problem in the United States today.

It's important to develop healthy eating habits early. To work well, to grow, and to resist illness your body needs a variety of nutrients. So remember to eat a selection of things from the basic four food groups every day. The groups are (1) fruits and vegetables, (2) breads and cereals, (3) milk and milk products, and (4) meat, nuts and beans.

Here are some ways to change your eating habits: Reach for carrot sticks, broccoli or unsalted, unbuttered popcorn instead of candy when you want a snack. Instead of drinking sugary soda, quench your thirst with fruit juice or water. For your next birthday party, try carrot cake instead of chocolate cake. Develop a taste for yogurt instead of ice cream.

Have whole-grain cereal for breakfast instead of sugar-coated stuff or doughnuts. For lunch, have a peanut butter sandwich, an orange and a glass of milk instead of a burger, fries and a shake. At dinner, have chicken or fish instead of red meat. And for a bedtime snack, try fruit instead of a chewy granola bar or cookies. Tips for Parents

The American Academy of Pediatrics has released the second edition of "The Pediatric Nutrition Handbook." One section of the book concerns fast foods, and provides some strategies for dealing with the fact that kids do eat these foods, yet still need to maintain a balanced diet. According to recent statistics, one of every 10 food dollars in the United States goes for fast food. The Academy suggests substituting milk, fruit juice or water for soft drinks or shakes, sharing shakes or french fries to reduce the effects of the low-nutrient, high-calorie food, or removing part or all of the bun on hamburgers and other sandwiches to reduce calories. The volume is available for $22.50 from the Academy's Publications Department, 141 Northwest Point Rd., P.O. Box 927, Elk Grove Village, Ill. 60007 or by calling 800-433-9016.

Another resource for keeping your kids on a healthy diet is available from the Center for Science in the Public Interest. The organization has published a poster listing the fat, sugar, salt and calorie content of about 250 fast foods, and fits nicely on a refrigerator door. It costs $3.95, and is available from CSPI, 1501 16th St. NW, Washington, D.C. 20036.