Sailboaters, bike riders, beer guzzlers and city trysters, long used to the casual pace and plain-jane ways of the Marina Restaurant on Daingerfield Island, will doubtless be surprised to find that when they come for a burger and beer early next month they will be doing so in a place called the After Deck Cafe'. Should they desire a more upscale menu, they can take their seats near the mesquite grill at a restaurant called Potowmack Landing. Even if all they want is a winch for a boat or widget for a bike, they'll get it from a clerk in a new store called, good heavens, the Spinnaker 'n Spoke.

Fortunately the ersatz boutique names are, just about, the worst of it. The new multipurpose facility, set to open in mid-January, is larger and more commodious than the World War II "temporary structure" it replaces on Daingerfield's northern point, and it was handsomely designed by the Washington firm of Giuliani & Associates to take advantage of the amazing long-distance views of the Capitol dome and the Washington Monument and, in the foreground, of the incessant comings and goings at National Airport.

Furthermore, plans devised by the National Park Service for developing the rest of the "island" -- named in the 19th century after a prominent Alexandria land-owning family, Daingerfield has been a lumpish, 100-acre peninsula on the west side of the Potomac for as long as anybody can remember -- are in most respects sensitive to the woodland beauty of the place. These plans, significantly scaled down from grandiose alternative schemes proposed four years ago, foresee a few simple adjustments that should make the park more accessible and convenient for more people while maintaining a healthy balance between human use and natural beauty.

"We decided that Daingerfield Island and Jones Point at the western end of the Woodrow Wilson Bridge should be the north-south anchors of the Alexandria waterfront, and that our main job was to retain as much of the natural green of both places as is possible in an urban setting," comments Michael Donnelly of the Park Service.

This is a good strategy. Treating the nearly three-mile stretch from Daingerfield to Jones Point as a whole ensures that future generations will be able to enjoy a variety of experiences at the river's edge, from urban pageantry to industrial muscle to the peace and quiet of the woods.

The northern part of Daingerfield Island has been used mainly for boating activities since just after World War II. The southern part has been left largely alone, though hidden in the hardwood forest and underbrush are a Park Service nursery and several high mounds of rock, gravel and dirt. By respecting this division the Park Service, with the commendable encouragement of the National Capital Planning Commission, has made sure that one of the region's increasingly rare natural waterfront habitats will remain as inviolate as possible.

The one major change proposed for the southern part of the island is an addition of a bicycle and hiking trail along the Potomac shoreline. This is fine. It will do no harm to the wildlife there, and it will give enterprising visitors a chance to bask in one of the more spectacular sound and light shows the area has to offer -- a most refreshing combination of city life and untouched nature, what with the spectacle of National's incoming jets, the humdrum military-industrial complex of Air Force, Navy and Blue Plains facilities across the river backed by Anacostia's wooded hills, the close-by rocks and trees and, above all, the broad, reflective expanse of the river itself.

On the northern tip of the park, the restaurants, which are capable of serving nearly 350 people at the same time, represent a major change. Obviously the Park Service was trying hard to serve several masters in this part of the plan. The nearly $3 million building was paid for by a private firm, Guest Services Inc., while the government put up approximately $300,000 for parking, landscaping and other improvements. In return for the privilege of operating restaurants at such a desirable location, Guest Services agreed to build and operate certain facilities -- the store, public showers, a multipurpose room -- deemed necessary by the Park Service.

It remains to be seen how this all works out -- whether, for instance, the increase in parking spaces (from about 70 to about 140) will be sufficient to the task -- but in theory the idea of putting this attraction at this particular spot is sound. What may be questionable is the scale of the operation. Will the influx of new visitors ruin the very atmosphere that made it attractive in the first place? This possibility makes the Daingerfield Island experiment worth watching closely. In no way should it be used as a carte blanche for the development of our national parks under a public-private partnership that tilts heavily in favor of the private sector.

But architecturally the new facility has a lot going for it. Its designers (Joseph Giuliani, with Vincent Rogers and Ken Brown) took the challenge of a complicated program and turned it into a crisp, shipshape building that contributes significantly to the visual appeal of the site.

The basis of the design is a galvanic pinwheel plan, with the kitchen and service areas snuggled efficiently in the center and the various public areas given succinct definition on the edges. (The store actually is a separate structure, but it reads as part of a whole). Thus the building is eminently approachable. Nearly surrounded by wood-surfaced decks for outdoor gatherings, it is literally open on all sides.

Adroit treatment of clear glass windows, with many rectangular openings of differing sizes, some of them spectacularly large, adds to the airy impression, both inside and out, while a staggered pattern of shed-like roofs gives the structure a dynamic profile. And the selection of materials -- vertical tongue-and-groove cedar siding treated with bleaching oil, cedar shakes on the roofs and white- or gray-painted trim at the eaves and around openings -- gives the place an appropriately nautical feel.

Clearly, these architects took great care to celebrate the virtues of the site -- its views and the pervasive, ever-changing light. A different design firm (Architectural Workshops, a division of Equipment Manufacturing Co. of Chicago) with a different idea handled the interior finishings of the restaurants. Unfortunately, the results are far from pleasing.

It is, in fact, depressing to compare the spaciousness of the main dining room, from simple ceiling trusses to treated cedar walls to clear glass windows, with the heavy oak furniture and paneling that overcrowd the space. The wood paneling and brass fixtures of the bar area in particular (called, what else, the Ward Room), would perhaps be at home in some dark, downtown den, but they are especially out of keeping with the casual, light-filled spirit of the place and the building.

Still, furniture, fixtures and names can be changed in time. I confidently expect to visit the Spinnaker 'n Spoke in the summer of '94 and find, instead, the Boat Supply Store (bike parts also for sale).