WASHINGTON -- Even as President Barack Obama's health care law expands coverage and transforms the way millions get medical care, it will have little effect on the total U.S. health care bill, a new government report finds.

Health care spending is expected to continue to surge over the next decade, hitting about $4.8 trillion in 2021, independent economists at the federal Centers for Medicare and Medicaid Services estimate.

That is up from $2.8 trillion this year and will push health care spending to nearly 20 percent of the U.S. economy by the beginning of the next decade.

The new estimates -- the latest annual projection from the federal government -- undermine claims by critics that the law will dramatically drive up health care spending. At the same time, they underscore some of the law's limitations.

"The growth rate of national health spending is projected to be fairly similar with or without the Affordable Care Act," said Sean Keehan, lead author of the report.

Total health care spending over the next decade will be about 1 percent higher -- or about $478 billion -- as result of the law, even with the federal government spending hundreds of millions of dollars to guarantee nearly all Americans coverage for the first time.

After the law is fully implemented in 2014, total health care spending is expected to grow more slowly than it would without the law, the report said.

The economists estimate that 30 million more people will gain coverage

Many of those people are expected to qualify for federal subsidies that will be available to people making up to four times the federal poverty line, or $92,200, for a family of four.

But the new estimates also show how little the law will do to fundamentally change the trajectory of health care spending.

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U.S. health spending likely to keep rising, with or without Obama's plan