PORTLAND, Maine — More than 500 people could lose their only source of health care if an India Street clinic can’t soon find a way to pay its bills.

The Portland Community Free Clinic, at 103 India St., offers primary and some specialized medical care to low-income Cumberland County residents without health insurance. For nearly two decades, the clinic was supported by a partnership between Mercy Hospital and the city.

But Mercy stopped its contribution of about $200,000 a year in 2011, and city funds dried up at at the end of September.

“We’re living on fumes,” said Caroline Teschke, Public Health Department program manager and administrator of the clinic. “Our need is urgent.”

Mercy and the city both continue to provide in-kind support. The hospital donates diagnostic, lab and referral services, while the city’s Public Health Department provides office space, liability insurance and other help.

“We want to be supportive, because the clinic is really an asset for Portland,” Health and Human Services Director Doug Gardner said.

But after picking up the cost of clinic staff salaries during the first quarter of its 2013 fiscal year, the city didn’t have the money to help past September.

“The hope there was that the three months would give us some breathing room until we found another strategy,” Teschke said. “But three months is not very long.”

Both Mercy and the city had hoped the clinic’s population could be served through other programs, including the federally qualified health center at 180 Park Ave. But the clinic’s patient load continues to remain above 500.

One of the reasons is that its after-work hours and lack of red tape often make it the only option for patients, Teschke said.

The clinic serves a population that falls into what Teschke calls “the poverty doughnut-hole” — earning too much to be eligible for public-health programs such as Medicaid, but not enough to afford health insurance on their own.

Clinic patients can earn no more than 250 percent of the federal poverty level, which represents a full-time wage of about $13.50 per hour for a single person.

“If you’re really poor, right at the bottom, then there is a system for you and someone to help,” she said. “But if you’re just a little above, then you’re in the swamp. Sure, there are low-cost [medical] services, but even low cost is a high barrier for people with almost no money.”

More than 100 physicians, nurses, counselors and others volunteer to keep the clinic in operation. And a fundraising group, the Friends of the Free Clinic, has sprung up to help.

Meanwhile, Teschke is applying for charitable grants and seeking other sources of funding. She said the clinic needs about $100,000 a year to remain open.

“We’ve leaned and meaned this budget down so that we can operate on $9,000 or $10,000 a month, but the need is solidly there,” she said. “Without the clinic, these patients will wind up in the emergency room.”