For more than 40 years, Providence Community Health Centers has performed a vital role in this city by providing medical care to many of its poorest citizens. Some 20 percent of Providence residents use the health centers' network of seven clinics for medical and dental services, relieving demand for charity care on the state's nonprofit hospitals, said Merrill R. Thomas, the chief executive of the nonprofit organization, which was established in 1968. Now the health centers are assuming an even greater role in one of the city's most distressed neighborhoods, Upper South Providence. With a combination of private and public financing that includes the use of historic tax credits, the group is building a 40,200-square-foot clinic on a three-and-a-half acre full-block site on Prairie Avenue, a street long associated with blight and economic despair. The clinic is to be the cornerstone of a medical-retail complex that will include a separate, stand-alone Walgreens drugstore and a rehabilitated brick factory that Lifespan, the state's largest hospital network, has agreed to lease for office space and possibly medical services and educational programs. In all, the $38 million project will have some 95,200 square feet of commercial and retail space in three separate buildings: the health center, which will be new construction, and two historic buildings that will be renovated and expanded. Demolition of the site's non-historic structures took place over the summer, and the health center's ground-breaking is planned for early next year. The development is poised to be a rare economic success story for Upper South Providence, a mostly residential community of some 5,000 people, most of them black and Hispanic, which was largely overlooked in the so-called Providence Renaissance that reshaped the downtown section of the city in the 1980s and '90s. It has the support of the city's Historic District Commission and Department of Planning and Development, as well as that of elected officials who represent Upper South Providence. 'The area I represent probably has the highest unemployment rate in Rhode Island,' said Luis Aponte, a Providence councilman whose district includes part of South Providence. Aponte said his constituents welcomed the development and were eager to take advantage of any job opportunities it might bring. 'It's a good news story with lots of promise,' he said. 