AUSTIN, Texas - Far from burdening the health care system, immigrants are helping to subsidize medical care for native-born Americans, according to a Harvard/Columbia University study weighing in on one of the flashpoints in debate over immigration. The report, released Monday and appearing in the current issue of the American Journal of Public Health, concludes that although many immigrants pay Medicare payroll and other taxes, they receive less than half as much health care as native-born families. Immigrant children, in particular, receive 74 percent less health care than U.S.-born children. Latino immigrants had the lowest health expenditures. The federal government will soon start paying $1 billion through 2008 to hospitals and doctors for providing emergency care to illegal immigrants. In May, hospitals, doctors and ambulance services in Arizona and other border states were able to start billing the federal government for emergency care they provide to illegal entrants. Arizona will receive up to $45 million a year for the four fiscal years that began last Oct. 1. Payments will be retroactive to that date, the government promised in May when it issued reimbursement guidelines. The Harvard/Columbia report, however, leaves unanswered questions about the impact illegal immigrants have on health care costs. Proponents of strict immigration control often argue that illegal immigrants are a drain on health care, but there is little definitive data to support that argument. "These findings help refute the popular mythologies that immigrants are placing a disproportionate burden on the health care system," said Sarita Mohanty, a physician who led the study while she was at Harvard. Researchers said the findings argue against proposals to restrict immigrants' eligibility for care, because such policies would save little money and place many - particularly children - at grave risk. The study does not indicate how much is spent on care for illegal immigrants because it was based on federal surveys that do not break out illegal immigration status. "That's the big criticism," said one of the study's co-authors, Olveen Carrasquillo of Columbia University's College of Physicians and Surgeons. But he said researchers probably would have found greater disparities had they been able to focus on undocumented immigrants. Many illegal immigrants also pay federal taxes, but most lack health insurance and receive even less health care. "If anything, we would have found even lower health expenditures for the undocumented," Carrasquillo said. As the nation's immigrant population has surged, states, lawmakers, taxpayers and hospital executives have expressed concern that illegal immigrants impose huge burdens on states' health care systems. Though most of the nation's uninsured are U.S.-born, hospitals write off as much as $2 billion a year in unpaid bills to treat illegal immigrants, according to some estimates. A federal Government Accountability Office study, however, concluded it is impossible to determine costs for treating the undocumented, because medical care providers rarely ask patients about their immigration status. Federal law requires hospitals, public or private, to treat all emergency room patients, regardless of their ability to pay.