RIVERSIDE, Calif. — In the Inland Empire, an economically depressed region in Southern California, President Obama’s health care law is expected to extend insurance coverage to more than 300,000 people by 2014. But coverage will not necessarily translate into care: Local health experts doubt there will be enough doctors to meet the area’s needs. There are not enough now.


Other places around the country, including the Mississippi Delta, Detroit and suburban Phoenix, face similar problems. The Association of American Medical Colleges estimates that in 2015 the country will have 62,900 fewer doctors than needed. And that number will more than double by 2025, as the expansion of insurance coverage and the aging of baby boomers drive up demand for care. Even without the health care law, the shortfall of doctors in 2025 would still exceed 100,000.


Health experts, including many who support the law, say there is little that the government or the medical profession will be able to do to close the gap by 2014, when the law begins extending coverage to about 30 million Americans. It typically takes a decade to train a doctor.


“We have a shortage of every kind of doctor, except for plastic surgeons and dermatologists,” said Dr. G. Richard Olds, the dean of the new medical school at the University of California, Riverside, founded in part to address the region’s doctor shortage. “We’ll have a 5,000-physician shortage in 10 years, no matter what anybody does.”


Experts describe a doctor shortage as an “invisible problem.” Patients still get care, but the process is often slow and difficult. In Riverside, it has left residents driving long distances to doctors, languishing on waiting lists, overusing emergency rooms and even forgoing care.


“It results in delayed care and higher levels of acuity,” said Dustin Corcoran, the chief executive of the California Medical Association, which represents 35,000 physicians. People “access the health care system through the emergency department, rather than establishing a relationship with a primary care physician who might keep them from getting sicker.”


In the Inland Empire, encompassing the counties of Riverside and San Bernardino, the shortage of doctors is already severe. The population of Riverside County swelled 42 percent in the 2000s, gaining more than 644,000 people. It has continued to grow despite the collapse of one of the country’s biggest property bubbles and a jobless rate of 11.8 percent in the Riverside-San Bernardino-Ontario metro area.


But the growth in the number of physicians has lagged, in no small part because the area has trouble attracting doctors, who might make more money and prefer living in nearby Orange County or Los Angeles.


A government council has recommended that a given region have 60 to 80 primary care doctors per 100,000 residents, and 85 to 105 specialists. The Inland Empire has about 40 primary care doctors and 70 specialists per 100,000 residents — the worst shortage in California, in both cases.


Moreover, across the country, fewer than half of primary care clinicians were accepting new Medicaid patients as of 2008, making it hard for the poor to find care even when they are eligible for Medicaid. The expansion of Medicaid accounts for more than one-third of the overall growth in coverage in President Obama’s health care law.


Providers say they are bracing for the surge of the newly insured into an already strained system.


Temetry Lindsey, the chief executive of Inland Behavioral & Health Services, which provides medical care to about 12,000 area residents, many of them low income, said she was speeding patient-processing systems, packing doctors’ schedules tighter and seeking to hire more physicians.


“We know we are going to be overrun at some point,” Ms. Lindsey said, estimating that the clinics would see new demand from 10,000 to 25,000 residents by 2014. She added that hiring new doctors had proved a struggle, in part because of the “stigma” of working in this part of California.


Across the country, a factor increasing demand, along with expansion of coverage in the law and simple population growth, is the aging of the baby boom generation. Medicare officials predict that enrollment will surge to 73.2 million in 2025, up 44 percent from 50.7 million this year.


“Older Americans require significantly more health care,” said Dr. Darrell G. Kirch, the president of the Association of American Medical Colleges. “Older individuals are more likely to have multiple chronic conditions, requiring more intensive, coordinated care.”


The pool of doctors has not kept pace, and will not, health experts said. Medical school enrollment is increasing, but not as fast as the population. The number of training positions for medical school graduates is lagging. Younger doctors are on average working fewer hours than their predecessors. And about a third of the country’s doctors are 55 or older, and nearing retirement.


Physician compensation is also an issue. The proportion of medical students choosing to enter primary care has declined in the past 15 years, as average earnings for primary care doctors and specialists, like orthopedic surgeons and radiologists, have diverged. A study by the Medical Group Management Association found that in 2010, primary care doctors made about $200,000 a year. Specialists often made twice as much.


The Obama administration has sought to ease the shortage. The health care law increases Medicaid’s primary care payment rates in 2013 and 2014. It also includes money to train new primary care doctors, reward them for working in underserved communities and strengthen community health centers.


But the provisions within the law are expected to increase the number of primary care doctors by perhaps 3,000 in the coming decade. Communities around the country need about 45,000.


Many health experts in California said that while they welcomed the expansion of coverage, they expected that the state simply would not be ready for the new demand. “It’s going to be necessary to use the resources that we have smarter” in light of the doctor shortages, said Dr. Mark D. Smith, who heads the California HealthCare Foundation, a nonprofit group.


Dr. Smith said building more walk-in clinics, allowing nurses to provide more care and encouraging doctors to work in teams would all be part of the answer. Mr. Corcoran of the California Medical Association also said the state would need to stop cutting Medicaid payment rates; instead, it needed to increase them to make seeing those patients economically feasible for doctors.


More doctors might be part of the answer as well. The U.C. Riverside medical school is hoping to enroll its first students in August 2013, and is planning a number of policies to encourage its graduates to stay in the area and practice primary care.


But Dr. Olds said changing how doctors provided care would be more important than minting new doctors. “I’m only adding 22 new students to this equation,” he said. “That’s not enough to put a dent in a 5,000-doctor shortage.”