THE SEASON has arrived when we begin to think about winter sports. The fun of a winter day may be found speeding down a snow-covered mountain on a pair of skis.

The feel of the cold wind blowing in your face and the tingle of a cold nose and cheeks hardly can be surpassed by any other winter endeavor. Almost anyone who can stand can learn to ski with only a couple of lessons. Nonetheless, skiing should be approached with some precautions: Being in the right condition and wearing the right clothes are important.

Downhill skiing requires good leg and upper body strength. In particular, it develops agility and balance. Cross-country skiing is probably the best single form of aerobic activity. It puts enormous demand on both upper and lower extremities. It is easier on the joints than running and uses more muscles than any other endurance exercise. You can burn up to 1,000 calories in an hour if you work exceptionally hard. Yet, cross-country skiing can be an extremely mild form of exercise if you do it slowly and gently.

Injury rates in downhill skiing depend on a skier's ability as well as on the level of conditioning. Accidents are more common when using longer skis than with shorter ones. Furthermore, higher speeds contribute to the possibility of injury. One of the most common injuries is the thumb sprain, which can be prevented by not strapping the ski pole to the wrist. The knee is also very vulnerable to injury during skiing. Improved strength in the muscle groups of the legs, abdomen and back will help reduce the risk of injury.

Many exercises can be used to condition one for the ski slopes including polimetrics, isometrics and isokinetics. Bench stepping, standing squat lunges, sitting-front leg raises and skating are just a few of the beneficial exercises that will develop the muscles used in skiing. Examples of exercise that can be used to improve agility and balance are the stork, the pogo hop and box jumping.

A few weeks before you hit the slopes, a good conditioning program will help you feel stronger, be more agile and have better balance skills.

Here are three exercises that will help you increase strength and flexibility for both downhill and cross-country skiing.

WALL SIT --

Lean your back against the wall with your feet in front of you and your knees bent in a 90-degree angle. Your arms and hands are relaxed by your sides. The spine should be straight with each vertebrae trying to touch the wall. Press your lower back into the wall; thus working your abdominal muscles. You should feel this in the front of your thighs. Hold this sitting position for a count of 15. Work up to one minute. Repeat twice a day.

THIGH FIRMER --

Sit up straight with your left leg extended (foot flexed), right knee bent (foot flat on floor) and hands on floor supporting you in back. Slowly move left leg up and down for 30 seconds. Switch legs and repeat. You should feel the workout in the front of your thighs, also it helps strengthen the muscles around your knee. Repeat twice a day.

LUNGE --

Stand tall. Take a giant step forward with your right foot. Bend your right knee until it forms a perfect right angle. Your knee should be directly over -- not in front of -- your ankle. Try to keep your left leg straight. Try to hold the position for 30 seconds. Stand up and switch legs and repeat. You should feel a good stretch in your legs. Repeat twice a day.

Before you put on your ski boots, warm up for 5 to 10 minutes of easy movements to increase the blood circulation through the body. Run or march in place, climb stairs, anything to warm up the muscles. Then stretch to increase your range of motion. Now you are ready for more vigorous activity. After you ski, remember to cool down by slowing down gradually.

Cold weather calls for special care when you are outdoors for long periods of time. One major hazard for skiers is hypothermia, the loss of the core body temperature. Hypothermia depresses the central nervous system, which results in an inability to shiver, sleepiness, and eventually coma. In addition, the lower temperature allows a lower metabolic rate, which further complicates temperature control of the body. Hypothermia is a life-threatening situation that requires medical care.

Skiers should dress in layers so that the amount of clothing can be adjusted as the temperature changes or as the body produces heat through exercise. Several layers of clothes allow air to be trapped between the layers and are warmer than one bulky garment. Cotton next to the skin is best because it absorbs moisture. Next use down, because it retains air, which is a greater insulator. Then add a top layer of nylon or some other wind-breaking material. A good wool hat is important to retain heat and will insure protection from losing too much body heat. In general, choose clothing that is lightweight yet allows for movement during skiing.

Contrary to some beliefs, exercising in cold weather will not "frost the lungs." Cold air picks up moisture and heat before it reaches the lungs. Your throat may be a little raw the first few days, but your body will soon adjust.

Racing down the slopes and cross-country skiing in the bright sunlight can give a dimension of pleasure to the cold days of winter. Being out of doors releases tensions built up from that closed indoor feeling. The child comes out in all of us when we go out to play in the snow. The thrill of winter need never grow old when we learn the sport of skiing.