When Dr. Brad Bellotte began his surgical residency at Allegheny General Hospital five years ago, his usual schedule put him on call every other night.

That meant he would arrive at the hospital at 5 a.m., work through the day and the night and through the next day before leaving at 6 or 7 p.m. Sometimes he'd leave as late as 10 p.m. At 5 a.m. the following day, he was due back at the hospital to begin the marathon again.

"That was kind of as bad as you can get," he said yesterday. Working for 120 of the 168 hours in a week meant he had little time for sleep. Nonetheless, he said, "I think it made me better, made me more efficient."

Thanks to changes adopted nationwide two years ago, most residents now work no more than 80 hours a week and no more than 24 consecutive hours.

Plenty of studies have shown that sleep-deprived workers are more likely to make mistakes, but medicine is a peculiarly demanding profession, and doctors have continued to debate whether the reduced hours actually translate into improved patient care.

Now, a pair of studies by the Harvard Work Hours, Health and Safety Group published in today's edition of the New England Journal of Medicine suggest that shorter hours indeed have beneficial effects.

One study, in which physicians and nurses observed first-year residents in intensive care units, found that those working the traditional schedule made 36 percent more serious medical errors than those who worked more limited hours.

One doctor, preparing to drain fluid from between the lung lining and the chest, was about to insert a needle into the left side of the patient's chest when a senior resident intervened and pointed out that the fluid actually was on the right side of the patient's chest.

In another instance, a doctor admitted a heart patient but failed to recognize that the patient also had Lyme disease. In another case, the doctor ordered an antibiotic to which the patient was allergic.

The second study found that first-year ICU residents on the limited schedule slept almost six more hours each week and had less than half of the attention failures on duty of residents on the traditional schedule.

In an accompanying editorial, the journal editor, Dr. Jeffrey Drazen, said the studies convinced him that it was time to replace the traditional system -- which made each doctor personally responsible for the patients he or she admitted -- with a team approach that allows doctors to get more sleep.

Dr. Carolyn Clancy, director of the federal Agency for Healthcare Research and Quality, likewise said the research led by Dr. Charles Czeisler, clearly shows that changing the design and structure of hospital practice is essential to improving patient care.

Dr. Eric Marderstein, chief surgical resident at UPMC Presbyterian, agreed that the article represents one step toward understanding the impact of the new work hours, "but I wouldn't call it conclusive."

"I'm still not completely convinced that the system is safer," he said. Extra sleep can certainly aid a doctor's performance, he said, but the shorter hours also mean doctors are handing off more patients to their colleagues for continued care. "And there's no good way to transmit 100 percent of the information necessary," he said.

"It's very difficult to stay up all night and work all day the next day," Marderstein said. The reduced hours thus are a benefit to the residents. "But the actual benefit to the patient is hard to measure," he contended.

Marderstein has done research on patient safety, reviewing adverse events at Presbyterian and trying to ascertain why they took place. In most cases, he found inexperience played the biggest role. But he acknowledged that patient medical records don't include information about how much sleep a physician had.

AGH's Bellotte, a neurosurgery resident and former chief resident, noted that the hospital has only six neurosurgery residents to provide coverage seven days a week . (Neurosurgeons serve six-year residencies, and AGH starts one new resident each year.) Cutting back hours for each resident creates scheduling headaches and reduces the number of physicians in the hospital, he said.

The reduced hours also mean residents have less time to learn necessary skills. Bellotte said neurosurgery residencies, which recently were extended from five to six years, may have to be extended yet again to compensate for the shorter hours.

Schedules that acknowledge a doctor's biological need for sleep will force physicians to develop better ways of sharing responsibility for each patient, Drazen said. Each physician on a team must learn the essential information about each patient, and that information will need to be stored in a standardized and accessible format.

"We must be more than awake -- we need to be awake and informed," Drazen wrote.