When Jean Mills, 73, sees her thyroid specialist at Presbyterian Medical Center, she, like most patients with health insurance, is charged a co-pay - her Keystone plan calls for $40.

But when she sees her primary-care doctor at the city's District Health Center No. 3, she pays nothing - not for a checkup, not for prescription drugs, not for any service at all.

That policy at the city's eight primary-care health centers - free care for everyone, with or without insurance - has recently raised questions of fairness and fiscal responsibility.

The Philadelphia Department of Public Health has proposed - and Mayor Nutter appears likely to include in his budget presentation tomorrow - new fees on a sliding scale for patients without health insurance.

With a budget gap looming and the clinics already stretched, however, how can the Health Department afford not to charge everyone at least something?

Officials say that the clinics have been free because most of their patients, even those with insurance, have little money. But they concede that the practice of not collecting co-pays must be revisited.

"Once you begin to charge one group, you need to look at how you charge every group," said Tom Storey, director of ambulatory health services, as the clinics are known internally.

Health Commissioner Donald F. Schwarz's proposal on fees, posted on the mayor's budget Web site, calls for "new sliding-scale fees for uninsured," with estimated revenue of just over $1 million.

"Rather than going after poor people," said Cathy Scott, president of District Council 47 of the American Federation of State, County, and Municipal Employees, "we think there are lots of other ways that the Health Department could save money."

Scott, whose union represents nurses and other professionals in the health centers, said that well before the uninsured proposal came up, she suggested to Schwarz that co-pays be collected from those who have insurance but that he was noncommittal.

About a fifth of the annual 334,000 patient visits are covered by private insurance or Medicare, so the union estimated that even if co-pays averaged as little as $10, the city would raise about $700,000 - a tiny amount compared to its other suggestions, but still a net positive.

In an interview last night, Schwarz said that part of his proposal, about improved collection of reimbursements, does call for charging co-pays for people with insurance. "We are required by contract to collect them," he said.

In fact, the clinics years ago charged some fees, recalled Lewis D. Polk, who served as health commissioner from 1972 to 1981. The comprehensive, primary-care health centers were created to replace outpatient clinics that were shuttered along with the old Philadelphia General Hospital in 1977.

Invoices were mailed to patients' homes because the health centers, many in high-crime areas, did not want to keep cash, according to officials from that era. People with private insurance or Medicare were billed the appropriate co-pays, while the uninsured were asked to pay on a sliding scale. (Medicaid, the federal-state program for the poor, generally has low co-pays or none at all.)

"They would just send you a bill," recalled Port Richmond resident Bill Arnold, who was uninsured when his family went to Health Center No. 10, on Cottman Avenue, in the mid-1980s. "We were just happy to pay the doctors who took care of us."

But when he lost his insurance again and visited the same clinic several years ago, he said, everything was free.

The bills never brought in a lot of money, said an official who was involved with health centers at that time but did not want to be named because he now runs clinics elsewhere. When officials realized that converting a new computer system to collect the payments would cost more than the payments would generate, they were dropped altogether.

That experience illustrates one of several balancing acts, both political and financial, that health-policy experts say must be considered when charging for care.

On one hand, research shows that co-payments mean "people have some incentive to be careful about the services they use," said Thomas Croghan, a senior fellow and expert in quality of care at Mathematica Policy Research. It also can be hard for elected officials to sell constituents on free services for the poor.

Yet a government goal is to get the poor into care.

"It is perfectly legal to waive Medicare co-pays in cases of financial need," Vicki Robinson, a U.S. Department of Health and Human Services official, said yesterday.

That was part of the city's thinking.

"In the past," said Storey, the clinics' director, "we have opted to forgo the direct charges since our patients are of quite limited means. Now we are faced with a budget crisis that requires us to consider direct charges as a means to continue operation of all eight primary-care health centers."

(Among the more draconian budget proposals given to Nutter are closing three of the centers as well as the city's nursing home.)

Along with fees of $5 to $20 for the uninsured, the Health Department has proposed charging for over-the-counter products such as aspirin and glucose test strips.

Also discussed - but "not part of our current strategy," Storey said - is the idea of charging co-pays for prescription drugs. The health centers filled 671,000 prescriptions for their patients last year, all free of charge.

Stepheni TrottBatipps goes to Health Center No. 2, at Broad and Morris Streets, at least once a month for monitoring of her diabetes and other issues. She has private health insurance but likes her doctor at the clinic near her home.

"I've never been asked for a co-pay, she said. "I'm not opposed. If it meant more revenue and more people would be served, I would pay."

Contact staff writer Don Sapatkin at 215-854-2617 or dsapatkin@phillynews.com.