Who says you can't have your cake and eat it, too? Or to put it another way, who says if you want to sail you have to own your own boat or rent someone else's?

Down at 600 Water Street SW -- an area finally emerging from planners' studies -- we boatless ones can find the Gangplank Sailing Association, which has just what we need.

The long and short of it is that for $250 for a full-season membership (May 15 through October 31,) you can sail one of the association's seven shiny, new 15-foot Albacore sloops on weekdays, evenings and weekends, with only a phone call needed to reserve one. There are informal races on Sundays. The gaily colored Albacores comprise the largest fleet of boats on the Potomac.

For people who knows how to sail but don't own their own boat, the association offers a perfect middle step: an opportunity to use a versatile craft for pleasure or competition, with no rental fees. Only members are permitted to use the boats. It's also a logical step for people who want to buy a boat but are unsure about whether a day sailer or a cruising boat best fits needs and purse.

An added attraction, of course, is the chance to be around boats and boaters. On a foul dy, talking over beer about sailing can be almost at much fun as being in the boat.

Experienced sailers accustomed to bigger, faster boats will find that the Albacores offer enough challenge to keep them from getting bored. They're fast and plane with the right wind and skipper. They're also good in light air -- of which there is often a surplus this time of year. The boats are equally well suited for the novice sailer. They may be used on the Washington Channel or the Potomac.

The association is limiting membership to 50 people; it also includes free guest privileges. As "Commodore" Giles Kelly puts it, "This arrangement is better than owning a yacht, and it's a hell of a lot cheaper."

There's also no cleaning of the hull in the spring, no bills from the marine supply store for sails, battens, lines, shackles, pins and whatnot. You don't have to remember to pay insurance, registration fee or slip charges, or have a trailer hitch grafted onto the back of your car.

The association also offers private or group sailing lessons at an extra charge for members and non-members who want instruction in these boats or just want to sharpen their sailing skills a bit more, as well as informal social get-togethers during the season.

Boats are docked at the Gangplank Marina on the Washington Channel. As anyone who's driven down Main Avenue in the last couple of years knows, a renaissance has been going on there:

The fish market is still there, as are the waterfront restaurants and the long-time resident Washington Marina Co.; but now the channel is becoming a full-fledged yachting center. The Capital Yacht Club continues to make its home there and will have updated waterfront facilities when Metro construction ceases to tear up its alloted space.

The gangplank is putting in new docks, expanding the number of slips, as well as adding a new building on the pier to house a boutique, a ship's store and a delicatessen where boaters can buy carryout lunches for floating picnics. There is to be office space for a marine insurance firm, an admiralty lawyer and a marine consultant. The new sailing association's activities are just one more step in the transformation along the water.

The National Park Service had docked the Lightship Chesapeake across the way on the Hains Point side. The ship, open to the public for tours, weighs anchor now and then for Alexandria and back, with tourists as its cargo. American University runs sailing classes from the lightship. Red and white O'Day Widgeon sloops owned by the Park Service are kept busy by earnest students trying to stay upright and out of each other's way. No doubt they provide entertainment for riverfront diners and nearby apartment dwellers.

And the new owners of the former Wilson Line are running excursions to Mount Vernon from their dock next to the marina.

For such a short trip from downtown, Maine Avenue is long on atmosphere. There a lot going on and the rebirth promises even more activity, color and fun for boaters or kibitzers. CAPTION: Picture, LOSTS OF PEOPLE SAIL ALBACORES WHILE DECIDING ON A LARGER BOAT; AND A CAPTAIN IS STILL A CAPTAIN. By Bob Burchette.