The Congressional Budget Office says the Internal Revenue Service will need $5 billion to $10 billion over 10 years to determine who is eligible for tax credits and other subsidies intended to make insurance affordable. The Department of Health and Human Services will need at least that much to carry out changes in Medicaid, Medicare and the private insurance market, the budget office said.

The law provided $11 billion for community health centers to serve 20 million more low-income people, including many expected to gain coverage under the law. Many Republicans, including President George W. Bush, have supported such clinics.

But Daniel R. Hawkins Jr., senior vice president of the National Association of Community Health Centers, said, “It’s unclear how we will fare in the new climate.”…

“House Republicans cannot enact legislation the president won’t sign,” said R. Scott Lilly, a former Democratic staff director of the House Appropriations Committee. “But the president cannot force them to appropriate money they don’t want to appropriate.”