WASHINGTON — Republican-leaning states will pick up a half dozen House seats thanks to the 2010 census, which found the nation’s population growing more slowly than in past decades but still shifting to the South and West.

The Census Bureau announced Tuesday that the nation’s population on April 1 was 308,745,538, up from 281.4 million a decade ago. The growth rate for the past decade was 9.7 percent, a slower pace than the 13.2 percent population increase from 1990 to 2000.

Only one state, Michigan, lost population during the past decade. Nevada, with a 35 percent increase, was the fastest-growing state.

The new numbers are a boon for Republicans, with Texas leading the way among GOP-leaning states that will gain House seats at the Rust Belt’s expense. Following each once-a-decade census, the nation must reapportion the House’s 435 districts to make them roughly equal in population, with each state getting at least one seat.

That triggers an often contentious and partisan process in many states, which will draw new congressional district lines that can help or hurt either party.

Texas will gain four new House seats, and Florida will gain two. Gaining one each are Arizona, Georgia, Nevada, South Carolina, Utah and Washington.

Ohio and New York will lose two House seats each. Losing one House seat are Illinois, Iowa, Louisiana, Massachusetts, Michigan, Missouri, New Jersey and Pennsylvania.

Florida will now have as many U.S. House members as New York: 27. California will still have 53 seats, and Texas will climb to 36.

In 2008, President Barack Obama lost in Texas and most of the other states that are gaining House seats. He carried most of the states that are losing House seats, including Ohio and Pennsylvania. Each House district represents an electoral vote in the presidential election process, meaning the political map for the 2012 election will tilt somewhat more Republican.

For the first time in its history, Democratic-leaning California will not gain a House seat after a census.

Starting early next year, most state governments will use detailed, computer-generated data on voting patterns to carve neighborhoods in or out of newly drawn House districts, tilting them more to the left or right. Sometimes politicians play it safe, quietly agreeing to protect Republican and Democratic incumbents alike. But sometimes the party in control will gamble and aggressively try to reconfigure the map to dump as many opponents as possible.

Last month’s elections put Republicans in full control of numerous state governments, giving the GOP an overall edge in the redistricting process. State governments’ ability to gerrymander districts is somewhat limited, however, by court rulings that require roughly equal populations, among other things. The 1965 Voting Rights Act protects ethnic minorities in several states that are subject to U.S. Justice Department oversight.

The U.S. is still growing quickly relative to other developed nations. The population in France and England each increased roughly 5 percent over the past decade, while in Japan the number is largely unchanged, and Germany’s population is declining. China grew at about 6 percent; Canada’s growth rate is roughly 10 percent.

The declining U.S. growth rate since 2000 is due partly to the economic meltdown in 2008, which brought U.S. births and illegal immigration to a near standstill compared with previous years. The 2010 count represents the number of people — citizens as well as legal and illegal immigrants — who called the U.S. their home on April 1.

White House press secretary Robert Gibbs sought Monday to downplay the possibility that 2010 census results would be a boon for Republicans. "I don’t think shifting some seats from one area of the country to another necessarily marks a concern that you can’t make a politically potent argument in those new places," he said.

States losing political clout may have little recourse to challenge the census numbers. Still, census officials were bracing for the possibility of lawsuits seeking to revise the 2010 findings.

The release of state apportionment numbers is the first set of numbers from the 2010 census. Beginning in February, the Census Bureau will release population and race breakdowns down to the neighborhood level for states to redraw congressional boundaries.

Louisiana, Virginia, New Jersey and Mississippi will be among the first states to receive their redistricting data in February.

The 2010 census results also are used to distribute more than $400 billion in annual federal aid and will change each state’s Electoral College votes beginning in the 2012 presidential election.

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Online:

www.census.gov