A doctors group expects a serious shortfall of family physicians in at least five states by 2020.

Population growth and rising numbers of elderly people in Nevada, Arizona, Florida, Texas and Idaho will make the need in those states most critical, said Dr. Perry Pugno of the American Academy of Family Physicians.

"As Americans age, they need more health-care interventions, and primary care is the most cost-effective way to help them maintain their health," Pugno said.

The number of U.S. medical graduates going into family medicine has been falling — by more than 50 percent from 1997 to 2005 — with many young doctors preferring specialties that pay better and offer more control over work hours.

The group scheduled a rally in Washington, D.C., on Wednesday, timed to coincide with the release of its workforce report, which estimates the number of family doctors must grow by 39 percent during the next 14 years to keep up with the nation's needs. All states will need more family doctors by 2020, the report says, with Nevada topping the list.

The doctors group wants Congress to increase Medicare payments to family doctors to help ease the shortage, Pugno said. The group also urges voters to question candidates about health care, an issue as important to those polled by the group as the war in Iraq and terrorism, Pugno said.

There are about 100,000 licensed family doctors in the United States, a number that has been growing slightly because doctors stay in the workforce longer, said Dr. Larry Fields, president of the American Academy of Family Physicians.