The last time I went sailing, perhaps the last time ever, I managed to bust a spinnaker pole while trying to jibe on Chesapeake Bay. The skipper's screams still scorch my ears. So I was predictably wary of windsurfing -- until I learned the other day that it has nothing to do with sailing. Among the crucial differences: Nobody orders you about when you windsurf. It is not, as Henry Beard has defined sailing, "the fine art of getting wet and becoming ill while going slowly nowhere at great expense." Windsurfing doesn't encourage you to dress funny. And even expert sailors, transplanted to a sailboard, can't lord it over blushing innocents like me. You don't need to be a sailor to know which way the wind blows. "It's blowing from the south," Alex Bryan said. It turns out he is a sailor, but he wasn't making a big deal of it. On the Virginia side of the Potomac River at Belle Haven Marina, he was teaching the basics of windsurfing. The day was hazy, the wind light: perfect for a lesson. "If you know how to sail," he told his eight students on the dock in Alexandria, "you might understand how a sailboard works, but that doesn't mean you'll be able to work it right away." The sailboard, invented by a couple of Californians in the mid-1960s, is an ambiguous marvel. As a result, the authorities in the District of Columbia are having a hard time deciding whether windsurfing is more like boating, which is permitted on the river, or swimming, which is banned. "It's debatable whether a sailboard is a boat or not a boat," said Lieutenant James Hampton of the D.C. Harbor Police. "Right now, we're waiting for an opinion from the corporation counsel." In the meantime, the cops hereabouts are letting folks windsurf. Below the Wilson Bridge at Belle Haven Marina, where the Mariner Sailing School started classes this summer, there's never been a problem: Maryland authorities, who patrol that part of the river, consider the pastime boating. A cross between a surfboard and a sailboat, a sailboard lacks a tiller but features a mast,which moves every whichaway on a universal joint, and a dagger-board for lateral stability. The standard model, which retails for $600 to $1,000, is 12 feet long and 26 inches wide, weighs about 40 pounds, sports 56 square feet of sail, and is capable of flying at more than 20 miles an hour. The preferred training model is slightly wider and more stable and has a tad less sail. Crouching behind a plastic chart in the middle of a semicircle, like a football coach talking strategy, Alex Bryan made squiggles with black crayon. Drawing arrows to indicate wind direction, pointy ovals to represent sailboards and curves for sails, he quickly filled the white space until it looked like a Kandinsky painting. Somewhere in the converging lines, he assured us, were revealed such mysteries as luffing, tacking and heading upwind. "I want you to get used to surfing more into the wind," he said. "Surfing downwind's too easy." Next Bryan ushered his charges to the ground simulator. It looked to be an outsized twister-board with mast and sail at the center. Bryan climbed aboard, planted his feet about a yard apart -- "You put the arch of your right foot at the base of the mast" -- grabbed something called the inhaul line and righted the assembly with a tug. When he did, the board twisted sideways to the breeze and the sail started to luff -- that is, ripple like a flag. With the inhaul line in his right hand, he took hold of the rubber-cushione tacking. "A sailboard doesn't have a rudder," he said, "so this is how you change direction. Your back is always to the wind. See? It's easy." It looked hard. One by one, the students mounted the simulator to be talked through some basic moves. Otto, a wiry chap with a German accent, and Mike, a sporty-looking fellow almost as tan as Alex, seemed to get the hang of things right away. Ann, after mumbling that she already owned a sailboard and had windsurfed many times -- at which Alex could manage only a double-take -- was more methodical but self-assured. I was the only one who fell off. I tried not to meet anyone's eyes. "Don't worry," the woman next to me said, her accent a clipped patrician. "In the water, it won't turn around so fast." This was Kee Cox, a mother of five from McLean who took up the sport last year, discovered that "it makes me very happy," and now helps instruct at the sailing school. She was to be my protector for the next few hours. She guided me to a sailboard, showed me how to attach the mast -- simply by fitting a plastic tab into a slot -- and ordered me to paddle out onto the Potomac. "Lie down on the board," she said, "just as if it were a surfboard." Not a surfer, I tried to imagine what that would be like. The water was a comfortable 70 degrees; it was also brown and muddy. A fish that had seen better days floated near the surface. While everyone agrees that the Potomac is cleaner than it used to be, there's debate as to whether you'd want to confirm that first-hand. Harbor policeman Hampton says he wouldn't, but Kee Cox, along with other devotees of the sport, says the river's clean enough. Senator Bob Packwood, an Oregon Republican who was Cox's student a few days after I was, holds with the windsurfers. "I've heard that the river's dirty, but it doesn't bother me," Packwooddsaid. "Of course, when I was growing up in Oregon, I swam in so many muddy swimming holes, I figure that if I don't have typhoid by now, I'll never get it." With the sail dragging behind in the water, I paddled out some 50 yards, pushed the sail to the side, found the inhaul line, and stood up on the sailboard. After a second or two, I fell off. I tried once more and fell off once more. This happened half a dozen times before the sailboard drifted back to the marina and I had to start paddling again. After about half an hour, Otto and Mike were gliding hither and yon; Ann was gliding hither. With Cox's help -- "Lean back," she called -- I had just about mastered pulling the sail out of the water, but once it caught the wind, it was still pulling me back in. Another half an hour, though, and I was starting to stay aboard. "I think you've got it now," Cox said. "I think you may be right," I said, before flailing my arms and falling in. I could pull up the sail, hold the boom and swing the mast back and forth, but I still couldn't do all that and talk, too. Before long, I successfully negotiated a slow tack and caught the wind, my board slicing headlong through the water. Alex Bryan glided alongside. "Maxin' out," he said. BOOM & BOARD Within minutes of downtown Washington, two places on the Potomac offer windsurfing lessons. The Mariner Sailing School at Belle Haven Marina, a mile south of Old Town on the George Washington Parkway (768-0018), holds four-hour classes, at a charge of $35 per person, weekdays, evenings and weekends. And next to the Watergate Apartments, the Thompson Boat Center also gives weekend lessons, $35 for four hours, or $50 for two three- hour stints. Call 333-4861 or 836-7873.