FACTBOX - Possible U.S. Republican vice presidential candidates

(Reuters) - Republican Arizona Sen. John McCain, who has clinched his party's nomination for the November presidential election, must choose a running mate.

Following is a list of Republicans who have been mentioned as possible vice presidential candidates, in alphabetical order:

* Charlie Crist, 51 - The Florida governor helped McCain win the nomination with his endorsement and might help him in an important battleground state that could go either Republican or Democratic in the November election. The charismatic former Florida attorney general, who notched an easy first term gubernatorial victory in 2006, is a vibrant campaigner. But he could face trouble with the more conservative wing of the party because of questions about his views on abortion.

* Mike Huckabee, 52 - The former Arkansas governor battled McCain for the party's presidential nomination and was the last major candidate to withdraw. The Baptist preacher is a social conservative who has support from the party's evangelical Christian base and is strong in the South.

* Bobby Jindal, 36 - Louisiana's governor and the first Indian-American elected head of a U.S. state. The Oxford-educated conservative would add youth and diversity to the Republican ticket. His domestic health policy experience would be a plus, but he might be seen as being too young, especially in contrast to 71-year-old McCain.

* Tim Pawlenty, 47 - The two-term Minnesota governor and early and steadfast McCain supporter could help with a Midwestern battleground state. Pawlenty would appeal to social conservatives but he is not well-known on the national stage.

* Robert Portman, 52 - A former congressman from Ohio who was the U.S. Trade Representative and budget director under President George W. Bush. A fiscal conservative, Portman could give McCain needed economic policy strength and would help in Ohio -- an important battleground state.

* Mitt Romney, 61 - The former Massachusetts governor lost the nomination to McCain. But Romney might have problems because of questions about his Mormon faith and because he once supported abortion rights. The businessman, who pumped about $35 million of his own fortune into his presidential bid, could do the same for a vice presidential campaign or help McCain with fund-raising. The former head of a private equity firm who also ran the Salt Lake City Winter Olympics, Romney would bring management experience to the ticket.

* John Thune, 47 - The senator from South Dakota would appeal to conservatives but McCain may not want to choose another senator as his running mate. After narrowly defeating the leader of the U.S. Senate Democrats, Tom Daschle, in 2004, Thune was seen as a giant killer, which gained him clout in the party. However he is also not very well known nationally.

(Reporting by Deborah Charles and Peter Cooney, editing by Patricia Zengerle)