WASHINGTON: Thousands of foreign-trained immigrant physicians are living in the United States with lifesaving skills that are going unused because they stumbled over one of the many hurdles in the path toward becoming a licensed doctor here.

The involved testing process and often duplicative training these doctors must go through are intended to make sure they meet this country’s high quality standards, which American medical industry groups say are unmatched elsewhere in the world. Some development experts are also loath to make it too easy for foreign doctors to practice here because of the risk of a “brain drain” abroad.

But many foreign physicians and their advocates argue that the process is unnecessarily restrictive and time-consuming, particularly since America’s need for doctors will expand sharply in a few short months under US President Obama’s health care law. They point out that medical services cost far more in the United States than elsewhere in the world, in part because of such restrictions.

The United States already faces a shortage of physicians in many parts of the country, especially in specialties where foreign-trained physicians are most likely to practice, like primary care. And that shortage is going to get exponentially worse, studies predict, when the health care law insures millions more Americans starting in 2014.

The new health care law only modestly increases the supply of homegrown primary care doctors, not nearly enough to account for the shortfall, and even that tiny bump is still a few years away because it takes so long to train new doctors. Immigrant advocates and some economists point out that the medical labor force could grow much faster if the country tapped the underused skills of the foreign-trained physicians who are already here but are not allowed to practice. Canada, by contrast, has made efforts to recognize more high-quality training programs done abroad.

“It doesn’t cost the taxpayers a penny because these doctors come fully trained,” said Nyapati Raghu Rao, the Indian-born chairman of psychiatry at Nassau University Medical Center and a past chairman of the American Medical Association’s international medical graduates governing council. “It is doubtful that the U.S. can respond to the massive shortages without the participation of international medical graduates. But we’re basically ignoring them in this discussion and I don’t know why that is.”

Consider Sajith Abeyawickrama, 37, who was a celebrated anesthesiologist in his native Sri Lanka. But here in the United States, where he came in 2010 to marry, he cannot practice medicine.

Instead of working as a doctor himself, he has held a series of jobs in the medical industry, including an unpaid position where he entered patient data into a hospital’s electronic medical records system, and, more recently, a paid position teaching a test prep course for students trying to become licensed doctors themselves.

For years the United States has been training too few doctors to meet its own needs, in part because of industry-set limits on the number of medical school slots available. Today about one in four physicians practicing in the United States were trained abroad, a figure that includes a substantial number of American citizens who could not get into medical school at home and studied in places like the Caribbean.

But immigrant doctors, no matter how experienced and well trained, must run a long, costly and confusing gantlet before they can actually practice here.

The process usually starts with an application to a private nonprofit organization that verifies medical school transcripts and diplomas. Among other requirements, foreign doctors must prove they speak English; pass three separate steps of the United States Medical Licensing Examination; get American recommendation letters, usually obtained after volunteering or working in a hospital, clinic or research organization; and be permanent residents or receive a work visa (which often requires them to return to their home country after their training).

The biggest challenge is that an immigrant physician must win one of the coveted slots in America’s medical residency system, the step that seems to be the tightest bottleneck.

That residency, which typically involves grueling 80-hour workweeks, is required even if a doctor previously did a residency in a country with an advanced medical system, like Britain or Japan. The only exception is for doctors who did their residencies in Canada.

The whole process can consume upward of a decade — for those lucky few who make it through.

“It took me double the time I thought, since I was still having to work while I was studying to pay for the visa, which was very expensive,” said Alisson Sombredero, 33, an H.I.V. specialist who came to the United States from Colombia in 2005.

Dr. Sombredero spent three years studying for her American license exams, gathering recommendation letters and volunteering at a hospital in an unpaid position. She supported herself during that time by working as a nanny. That was followed by three years in a residency at Highland Hospital in Oakland, Calif., and one year in an H.I.V. fellowship at San Francisco General Hospital. She finally finished her training this summer, eight years after she arrived in the United States and 16 years after she first enrolled in medical school.

Dr. Sombredero was helped through the process by the Welcome Back Initiative, an organization started 12 years ago as a partnership between San Francisco State University and City College of San Francisco. The organization has worked with about 4,600 physicians in its centers around the country, according to its founder, Jose Ramon Fernandez-Pena.

Only 118 of those doctors, he said, have successfully made it to residency.

“If I had to even think about going through residency now, I’d shoot myself,” said Dr. Fernandez-Pena, who came to the United States from Mexico in 1985 and chose not even to try treating patients once he learned what the licensing process requires. Today, in addition to running the Welcome Back Initiative, he is an associate professor of health education at San Francisco State.

The counterargument for making it easier for foreign physicians to practice in the United States — aside from concerns about quality controls — is that doing so will draw more physicians from poor countries. These places often have paid for their doctors’ medical training with public funds, on the assumption that those doctors will stay.

“We need to wean ourselves from our extraordinary dependence on importing doctors from the developing world,” said Fitzhugh Mullan, a professor of medicine and health policy at George Washington University in Washington. “We can’t tell other countries to nail their doctors’ feet to the ground at home. People will want to move and they should be able to. But we have created a huge, wide, open market by undertraining here, and the developing world responds.”

About one in 10 doctors trained in India have left that country, he found in a 2005 study, and the figure is close to one in three for Ghana. (Many of those moved to Europe or other developed nations other than the United States.)

No one knows exactly how many immigrant doctors are in the United States and not practicing, but some other data points provide a clue. Each year the Educational Commission for Foreign Medical Graduates, a private nonprofit, clears about 8,000 immigrant doctors (not including the American citizens who go to medical school abroad) to apply for the national residency match system. Normally about 3,000 of them successfully match to a residency slot, mostly filling less desired residencies in community hospitals, unpopular locations and in less lucrative specialties like primary care.

Over the last five years, an average of 42.1 percent of foreign-trained immigrant physicians who applied for residencies through the national match system succeeded. That compares with an average match rate of 93.9 percent for seniors at America’s mainstream medical schools.

Mr. Abeyawickrama, the Sri Lankan anesthesiologist, has failed to match for three years in a row; he blames low test scores. Most foreign doctors spend several years studying and taking their licensing exams, which American-trained doctors also take. He said he didn’t know this, and misguidedly thought it would be more expeditious to take all three within seven months of his arrival.

“That was the most foolish thing I ever did in my life,” he says. “I had the knowledge, but I did not know the art of the exams here.”

Even with inadequate preparation, he passed, though earning scores too low to be considered by most residency programs. But as a testament to his talents, he was recently offered a two-year research fellowship at the prestigious Cleveland Clinic, starting in the fall. He is hoping this job will give residency programs reason to overlook his test scores next time he applies.

“Once I finish my fellowship in Cleveland, at one of the best hospitals in America, I hope there will be some doors opening for me,” he said. “Maybe then they will look at my scores and realize they do not depict my true knowledge.”

The residency match rate for immigrants is likely to fall even lower in coming years. That is because the number of accredited American medical schools, and therefore United States-trained medical students, has increased substantially in the last decade, while the number of residency slots (most of which are subsizided by Medicare) has barely budged since Congress effectively froze residency funding in 1997.

Experts say several things could be done to make it easier for foreign-trained doctors to practice here, including reciprocal licensing arrangements, more and perhaps accelerated American residencies, or recognition of postgraduate training from other advanced countries.

Canada provides the most telling comparison. Some Canadian provinces allow immigrant doctors to practice family medicine without doing a Canadian residency, typically if the doctor did similar postgraduate work in the United States, Australia, Britain or Ireland. There are also residency waivers for some specialists coming from select training programs abroad considered similar to Canadian ones.

As a result, many (some estimates suggest nearly half) foreign-trained physicians currently coming into Canada do not have to redo a residency, said Dr. Rocco Gerace, the president of the Federation of Medical Regulatory Authorities of Canada.

In the United States, some foreign doctors work as waiters or taxi drivers while they try to work through the licensing process. Others decide to apply their skills to becoming another kind of medical professional, like a nurse practitioner or physician assistant, adopting careers that require fewer years of training. But those paths present barriers as well.

The same is true for other highly skilled medical professionals.

Hemamani Karuppiaharjunan, 40, was a dentist in her native India, which she left in 2000 to join her husband in the United States. She decided that going back to dentistry school in the United States while having two young children would be prohibitively time-consuming and expensive. Instead, she enrolled in a two-year dental hygiene program at Bergen Community College in Paramus, N.J., which cost her $30,000 instead of the $150,000 she would have needed to attend dental school. She graduated in 2012 at the top of her class and earns $42 an hour now, about half what she might make as a dentist in her area.

The loss of status has been harder.

“I rarely talk about it with patients,” she said. When she does mention her background, they usually express sympathy. “I’m glad my education is still respected in that sense, that people do recognize what I’ve done even though I can’t practice dentistry.”