The federal government predicted Monday that the supply of doctors who specialize in treating critically ill patients probably won't keep up with the demand of the country's aging population.

That's important, some groups say, because more doctors with such expertise could help save lives and money.

Critical care doctors, or intensivists, make up an evolving specialty, and one of the newest specialties to be certified under the American Board of Medical Specialties. About 2,000 such doctors specialize in treating patients in the nation's intensive care units.

In 2003, Congress asked the Health Resources and Services Administration to analyze whether the country would have enough critical care doctors. The agency projected two demand scenarios. Under the lowest projection, the expected supply of 2,800 critical care doctors in 2020 would meet demand.

But the agency said that scenario is unlikely. More hospitals are expected to increasingly staff their ICUs with critical care doctors. A larger percentage of ICU patients are likely to be seen by critical care doctors. As a result, 4,300 such doctors may be needed by 2020.

The government agency said lawmakers may want to establish some financial incentives to attract and retain more critical care doctors. It said financial recommendations went beyond the scope of the report, but some groups have called for more money for training. They also have called for expanding the J-1Visa Waiver program, which would let more foreign doctors practice in the United States, and they have called for an expansion of the National Health Service Corps, which pays for health professional's education in exchange for work in underserved areas.

Trade groups representing critical care doctors said increasing their ranks is important for the nation's health care system.

"The HRSA report is clear," said Dr. Peter D. Wagner, president of the American Thoracic Society. "The number of patients who are critically ill is growing. The number of critical care specialists trained to treat these patients is not keeping pace. A shortage is not only imminent but upon us, and, unless steps are taken to address the shortage, patients with life-threatening diseases and others being cared for in ICUs will suffer."