Windsurfing combines the challenges of surfing, sailing and waterskiing. The sailboard weighs under 60 pounds and can go wherever there are water and wind.

It is spartan - a 12-foot polyurethane board, a 14-foot fibreglass mast, a dagger-board, and a 56 square-foot sail. Hardly the thing for the white-creased-trouser sailor.

Sailing is done standing and there are no lines for sail trimming, only body weight and muscle. The mast mounts on a joint that swivels for sailing sail up or downwind.

The Windsurfer was designed in 1967 by Californians Hoyle Schweitzer, a computer analyst, and aeronautical engineer James Drake. Schweitzer, then 36, started in his back yard, building boards for his neighbors. He sought a boat that would "retain the adrenalin of surfing and freedom of sailing, while eliminating the hassles of both." Within two years he went full time; now over 10,000 Windsurfers have sold here and perhaps 130,000 in Europe. It is the largest single-design sailboat in the world.

Learning to windsurf taxes one's enthusiasm for what seems from shore to be a simple skill, but success makes it all worthwhile. "I had been towed in twice, almost run down by speedboats, and swamped by a 100-foot ferryboat," said one newcomer. "I kept plugging away because I knew once I got it, it would be one hell of a ride."

European Hans Lechleitner says the windsurfer feels like "a leaf in the wind."

But not a leaf drifting lazily in the breeze. Windsurfers are the fastest single-hulled sailboats in the world. At the Weymouth Speed Trials in England, the most noteworthy annual clocking event, a European sailboard windsurfer went a phenomenal 19.1 knots in a 24-knot wind. In yatchting's 1977 One-of-a-Kind Regatta the Windsurfer finished second in the centerboard class only for lack of wind. It passed all others when the breeze picked up.

One of the windsurfing world champions is Robbie Naish, a 14-year-old, 120-pound Hawaiian. There's a long-distance record held by native Marylander Ken Winner, who this spring sailed 100 miles along the Florida coast in just under 6 1/2 hours. The wind was blowing about 20 mph; he averaged 16.

The Mid-Atlantic windsurfer dealer is Pauli Pinkney, a 67-year-old retired research chemist. He and wife Mary, 64, keep busy year round teaching and racing.

Pinkney usually is nattily attired in shorts, shirt, shoes, socks, hat and sunglasses; his windsurfing prowess keeps him dry.

Asked why the sport has attained such phenomenal popularity in Europe, Pinkney said, "The Europeans have a completely different attitude towards health and sports than I think most Americans do. They're more willing to exert themselves and windsurfing is work. So many times when I'm saling, people come and ask me, 'Don't you get tired?' or 'Where do you sit?' Of course I get tired, but I don't sit down when I play tennis, either. That's what makes the sport so gratifying to me. It's frequently exhausting, sailing out there in high winds all afternoon, but it's always a challenge. I love to get people interested."

The essence of windsurfing is the challenge. Even if your first moment of success is lasts only 20 seconds, the experience will not be forgotten. It is feeling one with the wind. It is to the water what hand-gliding is to the skies. The body becomes a link between wind and sea, absorbing the motion and force while experiencing the freedom of a leaf drifting in the breeze. CAPTION: Picture, GOING BARE OUT THERE: WINDSURFING CHAMPION MATT SCHWEITZWER SAILS, SURFS, STRAINS AND STARES SIMULTANEOUSLY. Photo by Windsurfer.