Whether there is a national shortage of primary care providers is a matter of considerable debate. Some researchers contend the United States has too many doctors, driving overutilization of the system.

Image Massachusetts primary care practices like this one in Amherst have been trying to manage an influx of new patients. Credit... Christopher Capozziello for The New York Times

But there is little dispute that the general practice of medicine is under strain at a time when there is bipartisan consensus that better prevention and chronic disease management would not only improve health but also help control costs. With its population aging, the country will need 40 percent more primary care doctors by 2020, according to the American College of Physicians, which represents 125,000 internists, and the 94,000-member American Academy of Family Physicians. Community health centers, bolstered by increases in federal financing during the Bush years, are having particular difficulty finding doctors.

“I think it’s pretty serious,” said Dr. David C. Dale, president of the American College of Physicians and former dean of the University of Washington’s medical school. “Maybe we’re at the front of the wave, but there are several factors making it harder for the average American, particularly older Americans, to have a good personal physician.”

Studies show that the number of medical school graduates in the United States entering family medicine training programs, or residencies, has dropped by 50 percent since 1997. A decadelong decline gave way this year to a slight increase in numbers, perhaps because demand is driving up salaries.

There have been slight increases in the number of doctors training in internal medicine, which focuses on the nonsurgical treatment of adults. But the share of those residents who then establish a general practice has plummeted, to 24 percent in 2006 from 54 percent in 1998, according to the American College of Physicians.

The Government Accountability Office reported to Congress in February that the per capita supply of primary care physicians actually grew by 12 percent from 1995 to 2005, at more than double the rate for specialists. But the report also revealed deep shifts in the composition of primary care providers.

While fewer American-trained doctors are pursuing primary care, they are being replaced in droves by foreign medical school graduates and osteopathic doctors. There also has been rapid growth in the ranks of physician assistants and nurse practitioners.