SMACK DAB in the middle of Shaw -- once a gloomy of this city abandoned by merchants -- there is now an ultramodern Giant food store, the first chain-operated supermarket to open in the District of Columbia in 10 years. Not only is this new store defying the general marketing pattern in cities around the country; it is also delighting its long neglected neighbors who through the years have been trundling as best they could -- by bus and by feet, mostly -- to markets in other areas.

Yesterday during the store's second day of business, it was filled with shoppers proudly at home in their own neighborhood supermarket, contributing to an enterprise that is theirs in more ways than one -- 10 percent theirs, to be exact. That is the community's share of the stock. This neighborhood ownership is part of a joint venture with Giant, which owns a third of the stock, and the D.C. Development Corporation, a non-profit group financed by the city's housing authority, which owns the rest. The community's stake in the store goes beyond patronage and ownership too, for Giant's agreement to run the store includes a pledge to staff it with as many neighborhood residents as possible. Already, the opening has provided jobs for about 60 Shaw residents.

The man mainly responsible for this impressive local experiment is Giant's chairman emeritus, Joseph B. Danzansky, whose initiative and doggedness through the years made the project possible. Today his effort has caught the fancy of the new mayor, who says the Barry administration is prepared to help start similar ventures in other parts of the city. Giant, too, is interested.

Anacosta still needs help. In the wake of Safeway's decision to abandon its outlet at 14th Street and Good Hope Road SE, citizens group have spent coutless hours studying and arguing over proposals to operate a new supermarket at the site. But there are no assurances of the kind of sound financial arrangement that is essential to any such venture. Management by a supermarket chain, even a small one with a good track, is preferable to any gamble on a local operator with modest success. Too many neighborhoods have had their hopes raised and then dashed as commercial experiments have failed.

The city's commercial deserts can come alive only with continued vigorous support from Mayor Barry's administration, and with sound proposals that combined private-business expertise, government assistance and strong community organizations.