Updated

AUSTIN, Texas -- A surge of Hispanic residents and other population gains have Texas poised to add more congressional clout than any other state, but a partisan fight now looms over exactly where the new seats should go.

Texas is gaining four seats in the U.S. House, twice as many as Florida, the only other state to pick up multiple ones, according to new population figures announced Tuesday by the U.S. Census Bureau. All told, Republican-leaning states will pick up at least 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.

With Texas Republicans using recent elections to fortify their already solid control of the state Legislature, the political process of redrawing the state's congressional map would seem to benefit the GOP, too.

But Democrats say not so fast.

Boyd Richie, chairman of the Texas Democratic Party, said Hispanic and black population growth account for the additional seats, and he vowed to fight for a redistricting plan that takes their numbers into account.

"A legal and fair redistricting process must produce new congressional districts that reflect the Hispanic and African American population growth," Richie said. "Our Democratic numbers may be down, but we are not out. Democrats cannot and will not allow our voices to be silenced in this critical process."

The Census Bureau said 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, the lowest since the Great Depression. The U.S. population grew by 13.2 percent from 1990 to 2000. Michigan was the only state to lose 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, mostly 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.

In all, the census figures show a shift affecting 18 states taking effect when the 113th Congress takes office in 2013. The political power follows the high population growth, shifting toward the south and west and away from the industrial Midwest and northeast.

With reapportionment settled, the far more politically divisive process of redistricting is set to begin. In Texas, both major parties were bracing for a showdown over the state's new residents, beginning a fight that is sure to spark court action. But with Republican supermajorities in the Legislature, the temptation to run the table will be strong.

Rep. Pete Gallego, D-Alpine, said if the federal courts don't intervene to compel fairness, Republicans will likely produce a map that gives their party the advantage in three or perhaps even all four of the new seats.

"It is very easy to overreach when you're holding the map and have the pen in your hand," he said.

Despite the party's recent gains in the November legislative elections, Republicans won't have unchecked authority to draw the state's congressional map to benefit themselves.

Civil rights laws require that the interests of minority voters be protected as district boundaries are redrawn, and Texas is one of the states whose redistricting plans require "pre-clearance" by federal authorities under the Voting Rights Act.

Democrats are also counting on an assist from the Obama administration, which could have a significant voice in the pre-clearance process. It is the first time since the Voting Rights Act passed that the Justice Department will be in Democratic hands during the redistricting process.

Hispanic growth doesn't automatically translate into Democratic growth, though. Two heavily Hispanic congressional seats in South Texas flipped to Republicans this year. There also are several new Latino GOP members about to be sworn into legislative seats.

South Texas Rep. Aaron Pena, who recently left the Democrat Party and became a Republican, said Texas Latinos are more conservative than their counterparts in western states such as California and Nevada.

Pena, who sits on the House Redistricting Committee, said his "educated guess" was that Republicans would get three of the four seats.

"The Hispanic community is increasingly up for grabs," Pena said. "It's truly a swing population."

Texas already had the largest Republican delegation in Congress, holding 20 of the state's 32 seats. In the 2010 elections, the party picked up another three seats, two of them in heavily Latino districts in South Texas. With all the new growth, Texas will now have 36 seats and 38 presidential electoral votes.

Federal lawsuits are essentially guaranteed as part of the process, and if the past is any guide, the courts will have a major say in how the lines are finally drawn. In 2001, the Texas Legislature deadlocked on Congressional redistricting, leaving the federal courts to redraw all the districts. In 2006, the U.S. Supreme Court ordered that new lines be drawn in several districts to protect the rights of Hispanic voters in South Texas.

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.

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 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.

Apart from the respective four- and two-seat gains in Texas and Florida, Arizona, Georgia, Nevada, South Carolina, Utah and Washington are all picking up one new U.S. House seat. 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.

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.