Census Bureau data released on Wednesday showed that the number of uninsured shrank to 48.6 million people from 50 million in 2010, leaving 15.7 percent of the U.S. population without the most reliable means to pay for doctors, hospitals and life-saving procedures including cancer screenings.

The findings were part of a broader report on poverty in America, showing that the number of U.S. poor held steady, but the income inequality gap had grown.

In terms of health coverage, the United States posted its first improvement since 2007, with broad gains across age, racial and employment groups. Among the biggest winners were young people aged 19 to 25, who are now allowed to stay on their parent's plans under President Barack Obama's healthcare law.

That should come as good news for Obama as he battles for reelection against Republican presidential nominee Mitt Romney, who has vowed to repeal "Obamacare" on allegations that it amounts to a costly, unworkable big-government bureaucracy.

Analysts predict the number of uninsured Americans will fall more significantly in 2014, when more than 30 million people are scheduled to become eligible for coverage under Obama's Patient Protection and Affordable Care Act.

But today, there are still 18 million more people without insurance than in 1987, the earliest year cited by the Census Bureau report. Analysts said 2011's improvement stemmed largely from the impact of a weak economy and a burgeoning elderly population.

"Given the long-run decline in insurance, given the backdrop of increasing inequality, I'm not sure this is good news. But it's better news than we've come to expect," said University of Michigan health economist Tom Buchmueller.

MORE ELDERLY, POOR ELIGIBLE

The percentage of Americans with private insurance was little changed at 63.9 percent in 2011, the first year without a statistically significant decline since 2000. That stability was due largely to a 2.2 percentage point coverage gain among young adults.

"Private coverage rose among those under 25, apparently largely as a result of the health reform law, while private coverage continued to fall among those aged 25 to 64. And the two effects offset each other," said Robert Greenstein of the Center on Budget and Policy Priorities.

The ranks of those who depend on government health coverage swelled by 4 million people, split about evenly between the Medicare program for the elderly and disabled and the Medicaid program for the poor.

Analysts attributed the rise in Medicaid recipients to a substantial drop in income among those at the bottom of the income scale and a continuing trend among employers to reduce health coverage for lower-wage workers.

Medicare's ranks grew as more members of the baby boom generation entered retirement, underscoring concerns about the popular $590 billion program's future finances and its impact on the federal deficit.

Edmund Haislmaier of the conservative Heritage Foundation said the Census report mainly reinforced a picture of stalled job growth, a graying population and growing reliance on government assistance among lower-income people.

"It is similar to what you see in the labor market when the unemployment rate goes down, not because the number of jobs significantly increased, but because people were leaving the workforce - some of whom may be retiring," he said.

(Editing by Michele Gershberg and Todd Eastham)

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