WASHINGTON -- A new study says private insurers have an even bigger advantage than recently believed following recent changes in Medicare.

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The study finds the government is paying managed care plans 8.4 percent more per enrollee on average than traditional fee-for-service Medicare. That's about $2.75 billion this year alone.

The study was conducted by researchers at George Washington University and the Commonwealth Fund, which advocates research on health issues. The higher payments result from the Medicare bill that President George W. Bush signed last fall, which gives private insurers a broader role in the program.

"The policy of increasing payments to private managed care plans needs to be carefully monitored to determine if it is achieving its objectives and is making the best use of funds for Medicare beneficiaries," said Commonwealth Fund President Karen Davis.

The extra payments are aimed at increasing enrollment in health maintenance organizations and other managed-care plans, which supporters say will help lower Medicare costs over the long run.

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