Now that August is here, the end of summer is around the corner. Although it will stay hot for several more weeks, the days are already beginning to get shorter. The stores are filling up with back-to-school displays. You may even be starting to look forward to a new school year. Summer may be winding down . . . but that doesn't mean you can start getting lazy about good summer safety habits.

Today's column is designed to remind you of some ways to prevent accidents at the pool or on the beach, on your bike, on a hike, or just in your own backyard. Water Wisdom

Being around water is one of summer's greatest pleasures -- especially during this summer of '87, with its record-breaking heat wave. But water can be dangerous: According to the National Safety Council, drowning is the second-leading cause of accidental deaths of children below age 14. Car accidents rank first.

If you don't know how to swim, this summer would be a good time to learn. Ask your parents to contact your local chapter of the Red Cross to find out about swimming instruction. If you already know how to swim, you still must be careful at the pool and on the beach.

Always obey the lifeguards. And remember these tips: :: Never swim alone, even if you are a strong swimmer. :: Stay out of the water if you're tired. :: Don't run or fool around at the edge of a pool or lake. Many injuries happen when someone accidentally falls in the water. :: Dive only if you are absolutely sure the water is deep enough. Do not jump or dive into a pond or lake unless you are sure there are no rocks or branches hidden below the surface. :: In the ocean, swim along the shore. Do not swim straight out to sea. :: Stay out of the water during thunderstorms. Bicycle Basics

Summer is a great time for bike riding. To bicycle safely, always wear a helmet. Follow the rules of the road by biking with traffic, not against it. Like car drivers, bike riders must obey traffic lights, stop signs and lane markings.

Be extra careful at intersections, and watch out for cars pulling out of driveways. Nearly three quarters of serious bike accidents happen where driveways, alleys and streets cross each other.

It's also a good idea to make sure your bike is in super shape. This checklist will help. You should be able to answer "yes" to all 10 questions. If you can't, get your bike repaired before you ride it again: :: Is my bike's seat tight? :: Are my bike's handlebars tight? :: Does my bike's headlight work? :: Does my bike's horn work? :: Are the pedals on my bike in good shape? :: Does my bike have a chain guard? :: Do my brakes stop my bike quickly? :: Are there reflectors on my bike? :: Are my bike's tires in good condition? :: Do my bike's wheels have all their spokes? Keeping Your Cool

Like many people in the Washington area, you may have suffered more than usual from the heat this summer. Whether you're playing around the neighborhood or taking a hike with your family in the Shenandoah Mountains, it pays to keep your cool as much as possible. Feeling hot is uncomfortable and sticky; suffering from heat exhaustion or heatstroke can be dangerous.

Your body is designed to regulate its own temperature. That's why you sweat to cool off when it's hot and shiver to warm up when it's cold. But sometimes the heat is just too much. Getting a heat rash, experiencing muscle cramps, and feeling tired and listless are some signs that your body is just too hot.

Dusting your skin with cornstarch helps heat rash. (You can buy powdery baby cornstarch in the section of your supermarket or drugstore that sells products for infants.)

As you might expect, quiet rest in a cool place relieves tiredness. It's also important to drink plenty of water. During extra-hot weather, it's vital to keep your fluid intake high. If you don't drink to replace the liquid you lose by sweating, the chemical balance in your body can be disturbed. That's when muscle cramping and other symptoms set in.

The chemical upset caused by fluid loss is the culprit in serious health problems called heat exhaustion and heat stroke. People with heat exhaustion may feel confused, get sick to their stomachs or even pass out. People with heat stroke may get a high fever, stop sweating, have chills, feel dizzy and even have seizures. When this happens, emergency help from a doctor is required fast.

All these warnings may make you feel that getting through summer is a risky business. But if you use common sense, you can survive the "dog days" of August safely -- and still have fun.Tips for Parents

Publications from the National Safety Council can help reinforce basic accident-prevention practices for your family, no matter what time of year it may be. A summer-related pamphlet, "The Millers Beat the Heat," can be ordered for $1. Send a check or money order; do not send cash. Include a self-addressed business-size envelope with 22 cents postage on it. Write to: Marketing Operations, National Safety Council, 444 North Michigan Ave., Chicago, Ill. 60611.

Catherine O'Neill is a free-lance children's writer in Baltimore.