The shoppers in the Marine Barracks parking lot at 8th and I streets SE -- women with burlap bags, elderly men from nearby porches, suburbanites in search of a bargain -- carefully examined the plump Maryland tomatoes; red-ripe apples in wooden crates; green beans; bushels of beets, scallions and summer squash; earthy sweet potatoes; honeydew melons; and broad-leaf lettuce piled high in glistening stacks.

It was opening day at the People's Cooperative Open Air Market. The event last weekend kicked off a two-month period ending the first week in December in which local farmers and public housing residents will sell fruit, vegetables, eggs, fish and meat every Saturday from 10 a.m. to 3 p.m., giving area residents an opportunity to buy fresh food at below-supermarket prices.

"This is great," exclaimed Brenda Smith of Oxon Hill, Md. "The food is much fresher than in the stores and you can pick your own because it's not prepackaged."

Lavelma Anderson of Howard Road in Southeast, burdened with two heavy bags from a nearby Safeway, said, "I just came from the supermarket. I wish I had come here first. You can't beat these prices: sweet potatoes at 25 cents a pound, green beans at 35 cents. I'll know better next time."

The open-air market is the initial step of a two-stage program funded by an $11,000 grant from the District government, according to Dee Bates, project coordinator for the Poor People's Development Foundation. She said the private, nonprofit foundation, which is organizing the cooperative market program, plans to open three additional open-air markets in the District (tentatively, one in each geographical quadrant) next spring, followed by development of cooperative associations in public housing units citywide by the end of August 1982.

Bates says the development of cooperative food markets in low-income areas is a matter of survival. "The goal is to create a food source of which the general community can avail itself," she said. "Low-income people need an alternative to the inflationary, high prices of the supermarkets and smaller chain stores. The local farmers also benefit: by selling directly to the consumer they eliminate the middleman and thus retain a greater profit."

The Poor People's Develoment Foundation modeled the cooperative food markets on the successful D.C. Farmers' Market, which has been operating on Tuesdays and Thursdays in the RFK Stadium parking lot for just over a year. The 8th and I market, and its planned counterparts, will be smaller than the Farmers' Market, open on weekends for the convenience of working people, and strategically placed throughout the city so those that people without transportation can take advantage of the low prices and high quality of fresh-off-the-farm produce.

Unlike the Farmers' Market, which is for producers only, the cooperative markets will allow public housing residents a hand in the profit making. According to Al Smith, a D.C. Cooperative Extension Service agent, residents of the Arthur Capper and Ellen Wilson public housing developments will be able to purchase vegetables, eggs and grain at or below wholesale prices from local farmers with the foundation's help and sell them at two stands in the open-air market this Saturday. Last weekend, the market's three produce stands were run solely by farmers because the local residents were unable to obtain vending licenses in time for the coop's opening.

Cornbread Givens, president of the Poor People's Development Foundation and chairman of the Mayor's Commission on Cooperative Economic Development, views the participation of public housing residents in the cooperative market venture as the beginning of a multifaceted system of cooperatives that could help low-income people to help themselves.

"We are using food as the initial focus of our cooperative development program," said Givens. "People will always come together around food. Selling at the open-air market will allow the residents to accumulate capital which can be used to develop other cooperatives within the public housing units."

Givens stressed that the residents could use the money they earn in the market and the money granted by the city to form any type of cooperatives they want. He suggested maintenance, management and day-care cooperatives as possibilities, and said the profits could be used for startup services such as leaflet printing, transportation, and technical assistance.

According to Bates, the grant comes from the District government's Escheated Estate Fund -- money from the estates of deceased residents who have no heirs -- which the city uses to fund charitable organizations and to benefit low-income people.