Once a week, Ethel Milton used to take two buses from her apartment in Shaw to get to a supermarket in Cleveland Park. Her neighbor, Emma Dickens, 70, walked 10 blocks to a Safeway and Minerva Breedlove, another neighbor, shopped in Maryland where she worked.

Yesterday, all three women simply walked across the street from their homes for the opening of a new Giant supermarket at the O Street Market, 9th and O Streets NW.

The new store is the first major chain supermarket to open in the District of Columbia in 10 years, and its opening marks the return of the area's most successful supermarket chain to the inner city at a time when more and more middle-class blacks and whites are returning to once-shabby center-city neighborhoods.

In an innovative arrangement, the new Giant store will be jointly owned by Giant Food Inc., Shaw residents and a nonprofit corporation funded by the city government.

The Giant store is the centerpiece of the long-delayed O Street Market urban renewal project and symbolizes the transformation that has occurred in Shaw, once the city's worst slum, since the riots destroyed its major shopping areas along 7th Street.

The riots left Shaw badly scarred, with a glut of empty buildings, a high crime rate, an unsavory reputation and an overwhelmingly poor black population.

But today, whites make up 30 percent of its population, according to some estimates, and homes there sell for $60,000 to $80,000. It fast is becoming one of the city's most sought-after addresses.

"It's the good times for Shaw," D.C. Major Marion Barry said yesterday as he joined Shaw residents and Giant officials in cutting a white satin ribbon to open the new 24-hour-a-day store.

Milton Nicholas, chairman of the Shaw community group that has a 10 percent interest in the store, and Israel Cohen, Giant's president and chief executive officer, both stressed the need for community support if the store is to survive.

"With this joint venture, which is rare in this country, comes certain responsibilities," Nicholas said. "There is the responsibility to support this store, because some of its profits go back to the community."

"The only way this project will succeed is if both Giant and the Shaw community share mutually in the responsibility required," said Cohen in opening the company's eighth city store and the first in 11 years.

That responsibility requires "our mutual commitment to cleaniness, orderliness and fairness," Cohen said. "I promise you Giant will do its part."

Giant officials said they did not come to Shaw because of the changing racial makeup of the neighborhood but because it was a neighborhood in need of a store.

Like other big supermarket chains, it recognizes that an inner city store faces pilferage and vandalism problems unless the community helps maintain it.

In July, for instance, Safeway announced it would close its Anascostia store in December because the store was too small, its profit margin too low and pilferage too high.

In coming back to Shaw, the Giant store has to stock an array of products to meet the needs of its two diverse groups of customers -- poor blacks and upwardly mobile whites and blacks.

The store has a "gourmet foods" section with cavier, pickled mushrooms and Swedish pancake mix and a "gourmet produce" section with pomegranates and papayas. But it also stocks pork and beef neckbone, large galvanized trash cans and large packages of rice and beans.

"You have to please both [the poorer blacks and the more affluent whites and blacks]," Al Dobbin, senior vice president in charge of operations, said of the store's selection of products. "But it's not a unique store," he said, adding that all people eat basically the same food.

Dobbin said Giant was able to build a store in Shaw because the city had a large tract of land available after the old houses and stores that surrounded the old O Street farmers market were demolished for urban renewal.

New grocery stores usually need an acre of space for the store and three to four acres for parking, he said. The new store takes up three-quarters of an acre and eventually will have about 125 parking spaces, about 50 less than a suburban store that is not located in a shopping mall. Officials think the store can get by with fewer parking spaces because of its volume of walk-in customers.

The building is owned by Jim Adkins, who was selected by the city four years ago to restore the 93-year-old O Street farmers market and redevelop the rest of the block. Adkins leases the building to the three partners.

Adkins contracted with the construction division of Giant to build the store so that it would look like all other Giant stores.

Giant only has a one-third ownership in the store. The Shaw Community Development Corporation, Nicholas's group, owns 10 percent, and the D.C. Development Corporation, anonprofit group funded by the city housing department to encourage housing and business development, owns 57 percent.

The three operate the store under the name of Shaw Community Supermarket Inc., which signed an exclusive management contract with Giant to run the store. Giant will make all decisions on store operations and employes but the partners will make decisions on improvements to the store, said a Giant official.