NEW YORK—Of the five doctors in the New Albany Medical Group in rural northern Mississippi, only one can accept new patients. He specializes in geriatrics.

“Frankly, as people die off, he replaces them,” said Jason B. Dees, one of the physicians in the group in the Union County seat of New Albany. “We’re all pretty booked, and there’s still more demand.”

The new health care law will give 32 million more Americans the means to visit physicians who might not have the time—or financial incentive—to see them, according to Dees and 17 other doctors interviewed since President Obama signed the law March 23. While they applauded the ideal of greater access to medical care, they didn’t necessarily approve of how Congress decided to deliver it to people.

“They may have very easily given them a card that won’t buy them any more access to health care than they had before,” said Dees, 37, who graduated from the West Virginia School of Osteopathic Medicine in 1999.

The Patient Protection and Affordable Care Act put in motion the largest expansion of health care coverage since the creation in 1965 of Medicaid, for the poor, and Medicare, for people 65 and older and for the disabled. Obama signed a companion measure Tuesday to fully enact the law.

The result will be more patients and less money for doctors already feeling shortchanged by Medicaid and Medicare, said Richard Chudacoff, who applied to the Paris- based humanitarian group Doctors Without Borders after Congress passed the bill.

“If I’m going to do charity work, I’d rather do the charity work of my choosing,” the 50-year-old Las Vegas obstetrician and gynecologist said.

As many as 15 million of those joining the system will do so through Medicaid, according to the Congressional Budget Office. The act establishes a national floor for eligibility— to include anyone making below 133 percent of the federal poverty level— and extends coverage to childless adults, not just children, pregnant women, people older than 65 and the disabled.

Medicaid, paid for jointly by the federal and state governments, is administered by states, most of which have reduced reimbursements to physicians and hospitals since the recession gutted tax receipts. New Mexico trimmed its payments by 3 percent in December and Kansas by 10 percent in January. Fourteen states filed suit on the same day the president signed the law, disputing the constitutionality of burdens imposed on them by its rewriting of the rules.

Many doctors cannot afford to see government- insured patients as it is, according to Chudacoff, who said he accepts people with Medicare on principle, because his mother is covered by the program.

Private insurers generally pay more for services, with the average commercial reimbursement 28 percent higher than Medicare’s in 2008, data from the Medicare Payment Advisory Commission show. Medicaid pays even less—with compensation at 66 percent of Medicare rates for primary care services and at 72 percent for treatment by specialists, according to the Washington- based Urban Institute, a nonprofit group that analyzes social and economic policy.

The law mandates that primary care doctors be compensated for Medicaid services at Medicare rates beginning in 2013.

It is unclear how the law will affect individual physicians’ compensation, which vary widely. A family practitioner earns on average $173,000 annually, according to a 2009 survey by AMN Healthcare Services’ Merritt Hawkins unit, compared with $391,000 for a radiologist, $481,000 for an orthopedic surgeon, $344,000 for an anesthesiologist and $297,000 for a dermatologist.

But salaries tell only part of the story, because many doctors are small-business people who cover payrolls, said Tim Bartholow, a former family practitioner who is a senior vice president of the Wisconsin Medical Society in Madison.

In the 12-doctor clinic in rural Wisconsin where he worked until 2008, 48 cents of every dollar of revenue went to overhead such as rent and salaries, he said. Onequarter of the patients were on either Medicaid or Medicare, which in Wisconsin both reimburse physicians at less than 30 percent of the actual cost of a service, he said.

To cope with the discrepancy, Bartholow and his partners kept their office simple, he said, with painted rather than wallpapered walls and no decor elements such as the fish tanks and waterfalls that he has seen in some waiting rooms.

“If you’re not mindful about what it takes to keep the door open, eventually you won’t be able to stay in business,” he said. “I hear people talk about physician greed. And that can mean, ‘Do I have enough wealth for the latest toy?’ It can also mean, ‘Do I have enough money to pay for my nurse?’ ”