The union and others are pressing for federal legislation that would limit the number of hours doctors-in-training may work. Current guidelines set by the Accreditation Council for Graduate Medical Education limit interns and residents to an average of 80 hours a week, with no shift exceeding 30 hours.

The researchers say those limits don't give doctors enough time to sleep. A study published last fall, also in the New England Journal, found that interns who spent every third night working in the intensive care unit made 36% more medical errors than interns who kept less onerous schedules. They also made serious diagnostic errors 5.6 times as often as their well-rested counterparts, the study found.

Studies have shown that being awake for 21 hours impairs drivers as much as having a blood-alcohol concentration of 0.08, which is the legal limit for noncommercial drivers in the U.S., said Dennis Wylie, a consultant who analyzes human factors in motor vehicle operation and wrote an editorial accompanying today's study.

"It stands to reason that working for 32 hours would be worse," Wylie said.

But paring back the 80-hour work week would translate into longer residency programs if doctors are to complete the same amount of overall training, said Peter Carmel, a neurosurgeon and trustee of the American Medical Assn.

More important, it would mean finding money to pay for additional interns and residents. Neither Medicare — which funds resident salaries — nor hospitals have the resources, he said. Alternatives, such as nurses or physician assistants, are even more costly than residents, who typically earn $40,000 a year.

"Who's going to pay the additional salaries?" Carmel said. "That is going to be an extremely expensive choice for the public."