* Census data shows population shift to South and West
* Democratic-leaning states lose U.S. House seats
By John Whitesides
WASHINGTON, Dec 21 (Reuters) - Republican-leaning states in the U.S. South and West will gain political clout from U.S. population figures released on Tuesday, dealing a blow to President Barack Obama and his fellow Democrats that could linger for years.
The Census estimates show a population shift from Democratic-leaning states in the Northeast and Midwest to Republican strongholds like Texas, Utah and South Carolina, giving those states more seats in the U.S. House of Representatives.
The new figures, also could play a role in the 2012 White House race. The number of House seats determines each state's representation in the Electoral College, which is used to elect a president.
The release of the figures kicks off the once-a-decade, state-by-state fight over redrawing congressional lines to ensure each House district represents roughly the same number of people, as required by the U.S. Constitution.
The process, known as redistricting, is intensely partisan in many states as the parties fight to draw the boundaries in a way that makes each of the 435 House districts more reliably Republican or Democratic.
States that gained seats must determine where to place the new districts, with the dominant party in each state looking for maximum political advantage. States that lost seats will decide which districts to combine, meaning some House incumbents will have to face each other in the 2012 election.
"Now everyone can start to figure out who has a target on their back," said Tim Storey, a redistricting expert at the National Conference of State Legislatures.
The figures were released by the Census Bureau in its 2010 national population survey, conducted every 10 years.
Much of the population shift came from more Democratic states won by Obama in the 2008 presidential election to more conservative states won by Republican presidential candidate John McCain.
Of the eight states that gain at least one seat, five were won by McCain. Staunchly Republican Texas will gain four House seats, helped by a growing Hispanic population, while Arizona, Utah, Georgia and South Carolina -- all reliably conservative -- will pick up one each.
Three states won by Obama in 2008 gained seats -- Florida, which picks up two, and Washington and Nevada, which gain one each.
In 2008, Obama won eight of the 10 states losing seats, including New York and Ohio, which will lose two each. Losing one seat will be Iowa, Illinois, Missouri, Pennsylvania, Louisiana, Massachusetts, Michigan and New Jersey.
The states won by McCain that lose a seat are Missouri and Louisiana, which suffered a population drop after Hurricane Katrina in 2005.
The changes in House apportionment mean Obama could face a slightly tougher electoral map when he seeks re-election in 2012.
"If it was a really close race for the White House, this could be the difference," Storey said. (Editing by Vicki Allen)