WASHINGTON — The United States faces a shortage of as many as 90,000 physicians by 2025, including a critical need for specialists to treat an aging population that will increasingly live with chronic disease, the association that represents medical schools and teaching hospitals reported Tuesday.

The nation’s shortage of primary care physicians has received considerable attention in recent years, but the Association of American Medical Colleges report predicts that the greatest shortfall, on a percentage basis, will be in the demand for surgeons – especially those who treat diseases more common to older people, such as cancer.

In addition to the growing and aging population, full implementation of the Affordable Care Act in all 50 states would increase demand for doctors as more people are covered by insurance. But Obamacare’s impact will be small – just 2 percent of the projected growth in demand, the organization said. The supply of doctors also will grow but not nearly as quickly as the need, officials said.

“An increasingly older, sicker population, as well as people living longer with chronic diseases, such as cancer, is the reason for the increased demand,” Darrell Kirch, the AAMC’s president and chief executive, told reporters during a news briefing.

The organization called on Congress to raise the federal cap on slots for medical residents at teaching hospitals by 3,000 annually, at a cost it estimated would be about $1 billion per year. The government funds its share of training each U.S. physician – estimated at about $145,000 annually – via the Medicare program. Currently, those hospitals train 27,000 to 29,000 doctors each year.

In 2013, there were about 767,000 doctors practicing in the United States, the report stated.

Policymakers have debated the doctor shortage for years, with some arguing that certain types of doctors are clustered in cities and affluent areas, leaving rural and poor Americans critically underserved. The government runs programs to encourage doctors to practice in shortage areas.

In a 2013 paper in the journal Health Affairs, Linda Green, a mathematician who studies the health care system, argued that the projected shortage of primary care doctors may not occur. The move toward larger practices enable physicians to take on more patients.