The role of community health centers, which serve about 23 million people, is expected to grow as part of the national health care overhaul. A recent report by the National Association of Community Health Centers found that the nation’s 8,000 centers provide one-quarter of all primary-care visits for low-income people and saves the health care system $24 billion a year. Such low-cost primary care will be critical as more people receive coverage for the first time under reform and centers prepare to serve 40 million patients by 2015. That need led to a big increase in federal funding over the past several years. The stimulus bill gave the centers about $2 billion, and the health care overhaul law increased funding by $11 billion over 10 years. Yet, as Congress and the White House looked for ways to trim back the budget this month,they cut $600 million from that funding. And funding from some states, such as California, has dropped dramatically as state officials are forced to cover shortfalls associated with the recession.