New York City’s medical powerhouses are keeping the oldest and sickest patients in the hospital longer than their counterparts in other parts of the country. In the process, they are costing the government more money.

The finding, part of a study released yesterday by researchers at Dartmouth Medical School, is causing a stir in the city’s hospital community, which has complained of being under attack and financially shortchanged.

The study, which looked at Medicare enrollees who died between 2000 and 2003 at 4,300 hospitals, found that doctors who kept patients for longer periods of time relied too heavily on the more expensive hospital settings and could have saved Medicare $40 billion if they had been more efficient.

“The predominant factor in the New York market is that you have many more hospitals, all of whom are competing in a medical arms race to expand their capacity and to offer the latest and greatest,” a co-author of the study, Dr. Elliott Fisher, a professor of medicine at Dartmouth, said.

The New York City hospitals included in the study had particularly long lengths of stays compared to both the state and national average.

New York University Medical Center kept patients for an average of 32.1 days in the final six months of their lives – the longest of the hospitals reviewed. At Mount Sinai Hospital, that number was 24.4 days; at New York-Presbyterian Hospital it was 23.8, and at Lenox Hill Hospital it was 29.72. That state average was 20.4 days; the national average was 13.9.

Others studies at Dartmouth have found that patients who stayed in hospitals longer and saw more doctors did not have better outcomes. In fact, in some cases they had slightly worse outcomes, researchers said.

The president of the Greater New York Hospital Association, Kenneth Raske, called the latest study “totally lopsided.” He said it failed to account for the patients who lived and that it was “mathematically inaccurate” because hospitals receive lump sum, not daily, Medicare payments.

“There were fundamental questions that were not answered and to ignore them is to provide only half the story,” Mr. Raske, whose association represents 250 hospitals, said. “If you are going to allege that there are inefficiencies in providing service to those who died, what do you say about service provided for those who lived?”

Hospital executives defended the longer-than-average patients stays. The chief quality officer at New York Presbyterian, Dr. Mary Cooper, said state-of-the-art technology coupled with an academic-driven atmosphere means that doctors are exhausting every treatment option for their patients, which often results in longer stays. Still, she said the hospital uses the six-sigma business approach to ensure that it is running an efficient ship.

The chief medical officer at NYU, Max Cohen, acknowledged the longer-than-average hospitals stays at his institution, but said it was adding value for the community. “You’ve got to keep in mind that this study looked at chronically ill people in the last two year of their life,” Dr. Cohen said. “Our philosophy is that we’re not going to restrict access to care of these patients.”

The chief medical officer at the Centers for Medicare & Medicaid Services, Dr. Barry Straube, said the agency is looking at the problem the report raises and studying the possibility of a system that would financially reward hospitals that can use fewer resources without sacrificing patient care.