WASHINGTON is a walker's paradise. The District and surrounding suburbs have plenty of scenic pathways, riverside jogging trails and wide sidewalks. Tourists and natives stroll along the Mall between museum stops, commuters get their daily exercise by walking up steep Metro escalators, and others commute to work with their own two feet.

These days, walking isn't only healthy -- it's fashionable and convenient. Athletic shoe companies are designing new lines of walking shoes and newsstands are carrying a new magazine called Walking. Racewalking will become an Olympic event in 1988 and the sport is expected to open for women in 1992.

Racewalking or striding is gaining new participants who like the ease of just walking out their front door and being able to work out without investing in a gym or expensive home equipment. Also, many ex-joggers have traded running for walking because they've suffered too many knee and leg injuries from running too many miles. Walking is gentler on feet, knees and the back. It strengthens your heart and lungs and it's simple, safe and accessible to everyone.

Now, when I talk about walking or striding, I'm not talking about taking a leisurely after-dinner neighborhood stroll. Many experienced walkers are as fast as runners. Strolling will burn a few calories, but you won't get a cardiovascular workout. (You have to walk 20 to 30 minutes as fast as you can to get a good aerobic workout.) A good pace is about 120 steps a minute. At this pace, depending on your weight and the hill incline on which you're walking, you can burn from 200 to 300 calories in just 30 minutes. If you're new to striding, you might not be able to sustain that pace long enough to get the full workout benefit. So start slow. If you take 50 steps a minute, you're in good walking shape and you can increase your pace each week.

Don't push too hard too fast, though. If you can't talk normally while you're walking, slow down. A newcomer's goal could be to walk at least one mile in 15 minutes.

When you step out for a walk, keep your knees "soft" or slightly bent. With each step, you should land on your heels and let your feet roll until you push off with your toes. Start at a slow pace and let your body warm up. Give yourself about five minutes before you're going full speed at 120 paces a minute. New walkers should concentrate mainly on their feet and legs. But remember to stand tall and straight, head erect. Let your arms swing freely. To move from walking to striding you should swing your arms more vigorously and lengthen your stride.

Advanced walkers -- those who've been walking for exercise for at least 10 weeks -- can invest in a pair of hand or wrist weights. Two pounds in each hand is plenty of extra weight. Using weights while walking will increase your heart rate and upper-body muscle tone. Don't ever strap on leg weights,though. Leg weights can throw off your posture and stride and increase leg injuries.

You can also increase your exercise benefits by walking up a 15 degree slope. This requires four times as much effort as walking on a level surface.

Now while you're walking, try some of these upper-body exercises. While walking at a brisk pace, punch the air overhead, first with your right arm, then with your left. Punch with your right as you step with your left leg and punch with your left arm as you step with your right. When you punch, you should feel a lift in your ribcage. Exhale as you punch the air and ignore any funny looks you get from drivers-by. Punch for one full minute, to increase circulation and heart rate and build up shoulder muscles.

Next, continue walking briskly. Place both arms behind your back, keeping your arms straight with your palms facing away from your body. Move your arms in a scissor action. First, scissor your right arm over your left. Then reverse and repeat. Scissor for one full minute while maintaining your brisk pace. This will tone up your triceps.

Then, keep walking while holding your arms close to your body. Bend your elbows and extend your forearms straight in front of you. Your palms should be facing the sky, as if you were carrying a tray with both hands. Now, make fists with both hands. Keep your elbows stationary while you move your fists toward your chest. Then lower your fists to the extended position so that your arms are straight. Continue raising and lowering your arms for one full minute while you walk to tone up your biceps.

To work on your chest muscles, keep walking and extend your arms to the side. Now bend your elbows so that your fingers point toward the sky. Bring your forearms together. Try to resist while you bring your forearms together. More resistance means more muscle toning. Press your arms back to your sides again. Repeat for one full minute.

For more walking tips, write to the President's Council on Physical Fitness and Sports and request their free brochures, "Everybody's Walking for Fitness" and "Walking for Exercise and Pleasure." Address: President's Council on Physical Fitness and Sports, Washington, DC 20001.

Keep it up!