"People think one thing or another about this marina - they take one look and they either fall in love with it or they think it's the absolute pits."

George Stevens swung an arm in a wide arc over the little spit of land on the Potomac he comes to work on every morning.

Stevens is a partner in the Belle Haven Marina's sailboat rental service and Mariner Sailing School. Belle Haven, a few miles south of Old Town Alexandria on the George Washington Parkway, is one of a kind.

"We charge the lowest slip rentals anywhere in the area," Stevens bragged. "A dollar a foot for a slip and $15 a month for the moorings. Needless to say, everything is full."

But full of what?

Some of the weirdest floating and used-to-be floating contraptions imaginable make Belle Havenn home: battered old wooden cruisers, home-made trimarans two-thirds under water and dinky little sailing boats that have more freeboard than sail area. The owners spend half their time cleaning the jet soot off the decks - leavings from the National Airport fleet that roars overhead.

The scene doesn't bother Stevens. He's one of the ones who loves it here.

His fleet consists of a dozen sleek Flying Scots, which are very nice compromises between family daysailers and racing boats, plus a pair of Hobie cats and a smattering of Sunfish.

He suggested I come down some day when the wind was up and rent one of the Scots, take it an hour or so downriver and visit George Washington's Mount Vernon mansion the old-time way - by water.

It sounded good then and looked even better on a day that dawned clear, cool and breezy. It was blowing 15 knots out of the north and gusting to 20 and 25.

"You won't have trouble getting down there today," said Stevens."Getting back is something else again."

He squired me out to one of the moored 19-foot Scots in his powerboat, rigged the sails and pointed across the water.

"See that little stick off the point? That marks a mudflat. Go to the left and you run aground. Go right of the stick and you're all clear. Every one of my students knows that mudflat - intimately."

We set sail, he jumped back aboard the powerboat and I was off on a colossal series of reaches downriver. The foliage was brilliant midsummer green on both banks; whitecaps graced the muddy water. This was really sailing.

Good sailing, for sure, until Discovered the centerboard was stuck down and the machinery to grind it up was fouled. I clamped the rudder down with a jury-rig involving the bloom crutch and a paddle, then climbed under the foredeck to unfoul the rig, all the while scooting along downwind under full sail.

I almost had it fixed when the wind shifted and the boat swung wildly. I leaped back out and ran to the tiller but before I got ther I watched my self-tending rig collapse and the paddle flip overboard.

This set the stage for a series of uncontrolled turnabouts and maneuvers to recover the paddle. The first turnaround set me thinking.

"My word," I thought. "Where did all this wind come from?"

When the boat swung upwind I discovered it was heeled to the maximum, even when I spilled wind by keeping the mainsail loose.

"Long beat home," I thought, looking at the two or three miles I'd already traveled.

After a few misfires the boat finally swept by the paddle, which I collected. It was time to head back upstream. It was invigorating, in a word. A flying Scot is a fine boat, and one of the reasons for it is that she carries a lot of sail. One confused Scotsman in an unfamiliar Scot has his hands full keeping her right side up in breezes like that.

At last Stevens' muddy point hove into view and I swung wide areound the shoal, careered into the mooring area and, when faced with the requirement to stop, did the only manly thing and ran her hard aground. Stuck, I waited for Stevens to come to the rescue, which he did.

Later he and I went out again and we hauled back and forth below the Woodrow Wilson Bridge. It was a whale of a fine sailing day and we had a whale of a sail.

Belle Haven is something of a find for serious sailors - fine close-in place to sate the appetite for water and wind-borne thrills.

The rental fees for the Scots ( $19 for two hours weekends; $16 on weekdays) are modest, and it's even less per hour for longer sails. The Scot handles four adults easily, and Stevens puts on restrictions on downriver destinations. "We haven't had anybody fail to come back yet," he said.

For novices, his Mariner Sailing School offers week-long and shorter courses after which the average student can handle a rental boat.

Steven grew up racing Scots in the Potomac River Sailing Association at the Washington Sailing Marina. He knows the waters upstream and down, and many of his co-workers and instructors grew up racing against him.

His is a friendly little circle of serious racing sailors, right close to home. CAPTION: Picture, BOUNDING ALONG THE POTOMAC TOWARD GEORGE WASHINGTON'S HOUSE. By Angus Phillips.