On a chilly afternoon at a community clinic in Washington, three young doctors are busily laying the foundation for the health care law’s success.

Jacob Edwards flips through a manual on skin conditions, diagnosing a rash that looks like chicken pox. Jessica O’Babatunde consults her supervisor on treating an adolescent’s obesity, which is literally off-the-charts. And Julie Krueger peppers 3-year-old Daphauni with questions at her physical: How do you spell your name? What did you eat for breakfast? What’s your favorite vegetable? (Cheese.)

They are primary-care residents at Children’s National Medical Center. A third of their class has more than $200,000 each in student loan debt. At the end of residency, they can stay in primary care and earn $29.58 an hour. Or they can specialize and make $74.45. Over a lifetime, a medical student who specializes can expect to earn $3.5 million more.

The Obama administration – and, arguably, the American health-care system – desperately needs them to choose primary care.

Decades of research have confirmed that more specialists leads to more specialty care, which leads to a more expensive system. Now, with the passage of the Affordable Care Act, tens of millions of previously uninsured Americans will be looking for a primary-care doctor. It is no exaggeration to say that the success of the health care law rests on young doctors choosing to do something that is not in their economic self-interest.

The surprise of the health care overhaul, at least thus far, is that so many young doctors are cooperating. The number of American medical students matching into primary care residencies jumped 20 percent between 2009 and 2011, according to the Association of American Medical Colleges.

“Regardless of what people think about the health reform legislation, or what side of the aisle people are on, the debate shone a significant light on the importance of primary care,” says Glen Stream, president of the American Academy of Family Physicians. “There was more attention paid to the importance of primary care, the cost-effectiveness of it and that we’re facing a worsening shortage.”

That worsening shortage, he says, has to do with the economics, with nearly every incentive working against going into primary care.

“No matter what specialty you’re going into, your medical education costs the same,” Stream says. “Think about a medical student who is sort of interested in primary care and has got $250,000 in debt. People are often driven by financial incentives, and you basically get the outcome that you incent. Health care workforce is not different from any other sector in that regard.”

As with specialty doctors, specialty residents bring a hospital more lucrative business. A radiologist will earn a hospital $193 in Medicare reimbursements every hour, a primary-care doctor brings in $101, according to an analysis done for a congressional watchdog agency.

“What hospitals build, in terms of their residency training, has a lot to do with what business they’ll bring in,” says Robert Phillips, director of the Robert Graham Center, which studies health care workforce issues. “If they have a choice between funding a primary-care residency or one in cardiology, the cardiology residency will make them a lot more money. It’s a perfect storm that aligns the incentives against everything other than primary care.”

The greatest threat to the health care overhaul might not be the Supreme Court, which will issue a ruling in June. Or the shifting alliances of an election year. In the end, it’s more likely to be a lack of medical providers. If the law succeeds in extending health insurance to 32 million more Americans, there won’t be enough doctors to see them. In fact, the anticipated shortfall of primary-care providers, by 2015, is staggering: 29,800.

The Obama administration’s options to address that threat are limited. It does have Medicare, which covers the lion’s share of the cost of training medical residents: In 2009, it spent $9.5 billion on residents’ stipends, teaching physicians’ salaries and related expenses. But when Congress passed the balanced budget amendment in 1996, it capped the number of residencies that Medicare can pay for. Since then, hospitals’ slots have been tethered to 1996 levels.

The health overhaul, some hoped, would address that issue. But with the health insurance expansion’s $971 billion price tag – and the Obama administration goal to keep the law’s cost under $1 trillion – money for more slots didn’t turn up.

In the context of a $1 trillion overhaul, the White House’s main effort on this front seems modest: a $167 million sliver of the $15 billion Prevention and Public Health Fund created as part of the health care law.

“It’s good,” Stream says, “but it’s also a drop in the bucket.”

Last summer, the White House launched the Primary Care Residency Expansion at 82 hospitals across the country, with two strings attached: The programs must train residents dedicated to primary care, and the residents must work in underserved areas.

Medical students see good reasons not to sign up, because primary-care doctors often find themselves at the bottom of the pecking order. Research published this year in the journal Family Medicine found that medical students, even those planning to pursue careers in primary care, viewed the work lives of primary-care doctors more negatively than those of other doctors.

When the White House launched its residency program, it wasn’t sure medical students would show up. In fact, they snapped up all 172 slots paid for in its first year. “The thing we were really thrilled about is that all the positions were filled,” said Kathleen Klink of the Health Resources and Services Administration.

Atul Grover entertained such hopes nearly two decades ago as a young medical student who had watched President Bill Clinton and lawmakers battle over national health care legislation.

Health management organizations – which emphasized primary care as a way to limit the use of expensive specialists – were booming. So were primary-care residencies: 40 percent of medical students pursued them in 1997, an all-time high.

“There was a very clear signal,” says Grover, who completed a primary-care residency at the University of California at San Francisco. “If you want to be employed, you need to go into primary care. If you want to drive a cab, take something in anesthesiology.”

The Clinton health-care plan failed. Consumers revolted against HMOs’ limited networks, and the insurance plans rapidly lost market share. As for family doctors? They now earn about $150,000 less, on average, than anesthesiologists, according to the American Medical Group Association.

These days Grover and others say the current primary-care craze could end much the same way. The Prevention Fund’s residency financing runs out in 2015, and administration officials say there are no plans to extend the program.

“What I worry about is young physicians being told for a couple of years that this is totally worth it, and then it doesn’t pan out and then they get discouraged,” Grover says. “Unfortunately, I think we are moving in that direction.”