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WASHINGTON, Sept 10 (Reuters) - The number of people living in the United States without health insurance rose to 46.3 million in 2008 from 45.7 million a year earlier, a U.S. Census Bureau official said on Thursday.

David Johnson, who heads the Census Bureau's housing and household economic statistics division, told a telephone conference the data were collected in March of 2008 -- before the sharp economic downturn in the latter part of the year which saw many more people lose jobs and health insurance.

The new census numbers could feature in arguments over President Barack Obama's plans to overhaul the U.S. healthcare system and dramatically expand medical insurance coverage.

Johnson said that anyone who had insurance earlier in the year and lost it because of unemployment in the latter part of 2008 would have been counted in the report as having medical coverage -- meaning next year's uninsured numbers could be far worse.

The data showed that the number of people who were covered by private insurance fell between 2007 and 2008 and those enrolled in government health programs rose.

The report said that between 2007 and 2008 the number of those with private coverage fell to 201 million in 2008 from 202 million in 2007. The number of people enrolled in government programs climbed to 87.4 million in 2008 from 83 million in 2007, it said. (Reporting by Donna Smith; Editing by Sandra Maler)