Americans without health insurance are less likely to be given routine diagnostic tests, less likely to undergo key surgical procedures and more likely to die during their stay in a hospital than those with private medical insurance, according to the first comprehensive look at how financial factors govern hospital care in the United States.

The 35 million Americans without health insurance have long been known to have greater difficulty seeing a doctor and being admitted to a hospital than those with medical coverage.

But the new study, published in today's edition of the Journal of the American Medical Association, is the first to show that the insurance status of patients also makes a profound difference in how well they are treated by doctors after they have been admitted to the hospital.

The researchers stressed that they had no evidence that physicians were behaving unethically or deliberately jeopardizing the health of uninsured patients because of fears they could not pay their medical bills.

"Where it is clear-cut that a procedure or test needs to be done to save a person's life, I have no doubt that that test or procedure is done," said Jack Hadley, co-director of the Center for Health Policy Studies at Georgetown University and lead researcher on the study.

"But unfortunately for people without insurance, there are a lot of situations where this is not so clear-cut. . . . There are borderline situations where medical coverage is likely to be an important consideration" in deciding whether a test or procedure is given.

Health experts said that the findings -- which were based on an analysis of almost 600,000 patient records from around the country -- provide a powerful condemnation of the way in which financial considerations have intruded on the practice of medicine in the United States. Reform of U.S. medical insurance is considered to be a priority in the 102nd Congress.

"One of the myths we keep repeating is that we can't start rationing care in the United States. But studies like this show that we already are," said Jack Needleman, a health policy expert at Harvard University.

"The other myth is that U.S. health care is the best in the world. . . . At its best, U.S. health care is unmatched. But the health care system we have, with the millions of uninsured, is not the best."

People without health insurance are usually able to pay only about half of their medical bills themselves. The other half is generally absorbed by the hospital as a loss.

Because of this, some health experts have wondered whether physicians have tried to provide the cheapest possible care to the uninsured, either to make it easier for them to pay their bills or to limit the losses to the hospital.

The Georgetown study confirmed that doctors treat the two patient groups differently. It found that the uninsured, although they entered the hospital sicker than the insured, tended to stay in the hospital for a shorter period of time and receive fewer diagnostic tests.

They were also far less likely to undergo high-cost medical procedures. Total knee replacements, for example, were 75 percent less likely to be given to the uninsured than to the insured. Hip replacements were 45 percent less likely to be given to the uninsured and coronary bypass 29 percent less likely.

In all, the study concluded, the differences in care provided on the basis of insurance appeared to make the uninsured 1.2 to 3.2 times more likely to die during their stay in the hospital than those with private coverage.

Hadley stressed that this mortality gap may not be solely the result of insurance status, but that other socioeconomic factors could be involved. He and other experts also said that the study's results might reflect the fact that hospitals -- in a bid to make more money -- were giving the insured more care than they needed.