FACTBOX: Immigration in the United States

(Reuters) - Three weeks before Iowa kicks off the state-by-state battle to choose the Republican and Democratic candidates for the November 2008 presidential election, politicians are walking a fine line between appeasing anti-immigration sentiment without turning off Hispanic voters.

Here are some facts on immigration in the United States.

* There were an estimated 34.2 million immigrants in the United States in 2004, according to the U.S. Census Bureau. Of these, 18.3 million came from Latin America, 8.7 million from Asia and 4.7 million from Europe.

* An estimated 11 million to 12 million undocumented immigrants live and work in the United States, roughly one in every 20 workers, according to a study by the Pew Hispanic Center based on government figures.

* Some 1.1 million people were arrested crossing the U.S.-Mexico border illegally in 2006, most of them from Mexico and Central America.

* In 2006, President George W. Bush proposed an overhaul of U.S. immigration laws, offering a path to citizenship for many undocumented immigrants, together with a guest worker program, and tougher border and workplace enforcement.

* The legislation was opposed by Republicans in the House of Representatives who backed a tougher security program but were against any effort to grant citizenship rights to illegal immigrants.

(To read more about the U.S. political campaign, visit Reuters "Tales from the Trail: 2008" online here)

(Writing by Tim Gaynor and Paul Grant)