UPDATE 1- U.S. group says health premiums hit by uninsured

*Study says cost shifting raises insurance premiums

*Advocate says insured have financial stake in overhaul

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By Donna Smith

WASHINGTON, May 28 (Reuters) - U.S. families with health insurance are paying an estimated $1,017 more in annual premiums to pay for healthcare for the uninsured, according to a report released on Thursday.

The report by Families USA, an influential healthcare reform advocacy group, said doctors, hospitals and other health providers try to recover the cost of uncompensated care by increasing charges for those with private insurance. Insurers pass those costs to consumers in the form of higher premiums.

The report is likely to be used by lawmakers to help them make the case for an overhaul of the U.S. health system aimed at containing soaring costs and expanding medical coverage to the uninsured.

Ron Pollack, Families USA executive director, said the report shows that even those with employer-provided health insurance have a stake in expanding coverage to an estimated 46 million without insurance.

"That hidden health tax hits America's businesses and insured families hard in the pocketbook," Pollack said at a news conference. "They therefore have a clear financial stake in expanding coverage in health care reform this year."