Of the more than 8,000 physicians licensed to work in the nation’s capital, only 453 of them are primary-care doctors who spend more than 20 hours a week seeing patients, according to a report released Wednesday by the D.C. Board of Medicine.

The number of actively practicing primary-care doctors comes from a survey conducted when doctors renewed their licenses last year. It puts a number on a complaint that patients and health-care providers have long had: It’s hard to find a doctor in Washington.

Health-care experts have long bemoaned the looming shortage of physicians, particularly in primary care. Primary-care doctors will be especially important as a critical phase of President Obama’s health-care law gets underway Tuesday. That’s when Americans who lack medical insurance have their first chance to sign up for coverage under the new health insurance marketplaces that are supposed to open for business.

“It’s likely that will put the squeeze on, and being able to see a primary-care doctor is going to get worse,” said Janis Orlowski, head of the board.

The District has among the fewest uninsured residents of any place in the country: An estimated 42,000 people, or 7 percent of the District’s population, are uninsured.

Officials running the District’s new health insurance marketplace, or exchange, are hoping that another group of people, an estimated 25,000 people who buy insurance on their own rather than getting it from employers, might also use the exchange to find cheaper coverage.

The number of actively practicing primary-care doctors refers to those who practice internal medicine, family medicine, obstetrics and gynecology, and pediatrics. But Wednesday’s figure is considerably lower than the 918 actively practicing primary-care physicians reported in 2010 by the board, when it conducted its first survey of the physician workforce in the nation’s capital.

Orlowski said the most recent survey is more accurate because it focuses on physicians who spend more than 20 hours caring for patients. The earlier questionnaire may also have counted specialists as primary-care doctors, she said.

In general, the District and neighboring Maryland probably have more physicians per capita than elsewhere in the nation, health-care policy experts said. The concern has less to do with how many doctors there are than where they are.

Like in the previous board report, the latest survey found that actively practicing primary-care doctors are clustered in wards 1, 2, 3 and 5, near the city’s hospitals. But many of the District’s uninsured population live in wards 4 and 7, where there are few such physicians.

“If all the physicians are located in Northwest, and only a tiny population is in Southeast or Northeast, then you’ve got access problems,” said Atul Grover, chief public policy officer for the American Association of Medical Colleges. Maps of the District show very few physician offices in wards 7 and 8.

Even if uninsured residents in those wards sign up for new health insurance coverage, “they’re going to have access issues even if you give them an insurance card,” Grover said.

The survey also found that about 25 percent of the 4,790 responding physicians said they thought that the health-care law will have a positive effect on health care in the District.

Nearly all said the main reason would be that implementation of the law would increase access to care.

The survey also spotted some encouraging signs. Among the 453 actively practicing primary-care doctors, 85 percent were accepting new patients. There was also no evidence that doctors were planning to leave the city for Maryland or Virginia.

To conduct the survey, the Board of Medicine sent voluntary questionnaires to 8,466 physicians who renewed their licenses last year. About 56 percent — or 4,790 actively licensed doctors — responded. Of those, 1,354 identified themselves as primary-care doctors and 3,436 said they were specialists.