Community health centers treat 22 million Americans and account for an estimated one-fourth of all primary care visits by low-income people. Research shows they save the health system money. President George W. Bush doubled the program; President Obama's initiatives are expected to double it again.

Yet the centers - and their 700,000 patients - could be facing new obstacles in Pennsylvania.

Gov. Corbett's draft plan expanding Medicaid to cover more than 500,000 uninsured people lets insurers exclude community health centers from their networks.

It also changes the longtime funding formula, effectively cutting by more than half the reimbursements these centers would receive for new patients.

"With their financial picture already fragile, losing revenue just as patients are increasing is rolling the dice in a potentially dangerous way," said Natalie Levkovich, executive director of the Health Federation of Philadelphia, a collaboration of more than 40 city and suburban clinics.

These centers - Federally Qualified Health Centers - are providers of choice for the uninsured.

"We believe there is tremendous value in FQHCs," said Eric Kiehl, a spokesman for the Department of Public Welfare, which oversees Medicaid in Pennsylvania. With a big coverage expansion, Kiehl said, the administration hopes the uninsured "will now have a [private] doctor to go to to get some of those basic services . . . and not have to rely so heavily on the FQHCs."

Many share that belief. Evidence suggests just the opposite.

In the three years after Massachusetts reformed its health system in 2006, providing a template for "Obamacare," the number of patients served by local clinics rose 31 percent, researchers reported in the the Archives of Internal Medicine. Uninsured patients who initially sought out health centers because they could be treated for little or nothing did not want to leave.

"People said this was their first choice," said lead author Leighton Ku. "They offered the type of services they wanted," were nearby, and understood the language and culture. And the centers, unlike many private doctors, considered it part of their mission "to take on the surge" of newly insured patients, said Ku, director of George Washington University's Center for Health Policy Research.

The clinics are designed for underserved communities. They often include primary care, behavioral health, pediatrics, dental, nutrition, and social work. Perhaps for that reason, according to another study Ku cowrote, total medical costs, including hospitalizations, averaged 24 percent less for the centers' patients than for those of similar backgrounds who saw other providers.

Their patients, however, are far more likely than wealthier people to have hard-to-manage medical conditions - maybe untreated for years - like diabetes and depression, often in combination.

"We do really well at what we do. We know our patients," said Susan Post, executive director of the Esperanza Health Center in North Philadelphia. Two-thirds of its 11,000 patients are on Medicaid.

To pay for the extra care, Medicaid programs nationwide add supplemental payments to make up the gap between what Medicaid pays and what the care costs. That payment represents 56 percent of what Esperanza receives for Medicaid patients.

Corbett's draft alternative to Medicaid expansion cuts out the supplemental payment.

The change does not apply to current Medicaid patients; if it did, administrators said, some nonprofit clinics would close. Still, taking on new patients for less than half the pay would likely limit their ability to expand, and would force service cuts, they said.

The Philadelphia Department of Public Health runs eight health centers that treated 83,000 patients last year. The city foots the bill for the 53 percent who have no insurance. The vast majority would be eligible for coverage if Pennsylvania expanded Medicaid.

As envisioned by Obamacare, the federal government would pick up 100 percent of the city's tab for those patients through 2016, gradually falling to 90 percent. Corbett's plan would use the same federal money to subsidize commercial insurance policies for the same population, while killing supplemental payments to the clinics.

It also would eliminate a federal requirement that health centers be in insurers' networks.

If they took up that offer, it could mean no reimbursements for clinics that serve a large slice of the new patients the Affordable Care Act was meant to cover. Independence Blue Cross, the largest regional insurer, declined to say what it might do.

Kiehl, the state welfare agency spokesman, said the changes reflected the governor's overall theme of relying on the private market. "That is the way all other providers work with commercial coverage," he said.

Kiehl said officials were working as quickly as possible to review more than 1,000 public comments on the draft before submitting a final version to the federal government.

At Esperanza's newest location on North Sixth Street recently, new patient Marissa Melnyck, 35, a mother of two, described minor chest pains and reviewed her history, which included diagnoses of bipolar and post-traumatic stress disorders.

"Mentally, I think I'm in a good spot," she said. She works part-time preparing tax returns. Medicaid covers her drugs and two weekly therapy sessions, individual and group, about 100 a year.

One part of Corbett's draft that affects current recipients as well as new ones would cut that benefit to a maximum of 40 or 50 sessions, depending on whether a patient is low- or high-risk.

Asked whether there would be a way to get more, the state spokesman said patients could appeal to insurers for an exception.

215-854-2617 @DonSapatkin