Reuters) - Alabama and Mississippi hold presidential primaries on Tuesday, with polls showing three of the four Republican candidates locked in close races in each state.

The stakes are high for former U.S. House of Representatives Speaker Newt Gingrich and former U.S. Senator Rick Santorum, as they fight for support among conservatives and try to cut into the support for frontrunner Mitt Romney.

A win in either of the two Southern states, the latest to hold nominating contests in the race to pick a challenger to face President Barack Obama in the November election, would be a breakthrough for Romney's campaign.

Texas congressman Ron Paul is not seen performing well in either of the open primaries, in which Democrats, Republicans and Independents can vote across party lines. Voter turnout is expected to be high.

Details follow on the two states and the primary races:

Alabama

* Public Policy Polling surveys showed Gingrich, Romney and Santorum were within 2 percentage points of each other, inside the margin of error.

* Alabama sends 50 delegates to the Republican National Convention in Tampa, Florida. They are awarded proportionally for each of the state's congressional districts and also according to the statewide vote.

* In 2010, 68.5 percent of Alabama residents were white, 26 percent black and 4 percent Hispanic, according to U.S. Census data.

* In 2008, 77 percent of Alabama voters in the Republican primary said abortion should be illegal, according to exit polls. Seventy percent said they attended church weekly.

* Unemployment in Alabama was 8.0 percent in December 2011, compared to the national average at that time of 8.5 percent, according to the U.S. Bureau of Labor Statistics.

* Republican presidential candidates who have dropped out of the race will still be on the ballot, including Texas Governor Rick Perry, U.S. Representative Michele Bachmann and former Utah Governor Jon Huntsman. Georgia businessman Herman Cain will not be on the ballot.

Mississippi

* Public Policy Polling surveys showed Gingrich led Romney 33 percent to 31 percent, with Santorum at 27 percent.

* Mississippi has 40 delegates. Of those, more than half will be awarded proportionally, according to the statewide vote and another 12 will be per congressional district, the Mississippi Republican Party website said.

* Sixty-nine percent of those who voted in the 2008 Republican primary identified as Born-Again or Evangelical Christians, according to exit polls. Seventy-two percent of voters also said abortion should be illegal.

* Romney, a former Massachusetts governor, was endorsed by Mississippi Governor Phil Bryant.

* Unemployment was 10.4 percent in December 2011, compared to the national average at that time of 8.5 percent, according to the U.S. Bureau of Labor Statistics.

* In 2010, almost 60 percent of the state's residents were white, 37 percent were black and 2.7 percent were Hispanic, according to the U.S. Census.

(Reporting By Lily Kuo; Editing by Paul Simao)

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