FACTBOX - U.S. states voting on March 4

(Reuters) - Four states -- Texas, Ohio, Vermont and Rhode Island -- vote in U.S. presidential candidates in party nominating contests on Tuesday. Here are some facts about the vote in each state:

TEXAS

* The Democratic vote is considered a must-win for Sen. Hillary Clinton who is trying to stay alive in her fight against rival Sen. Barack Obama while Sen. John McCain is expected to easily win the Republican vote.

* Voting ends in most of the state at 0100 GMT on Wednesday, with a tiny portion of the state finishing at 0200 GMT.

* Clinton's hopes in Texas rest heavily on her ability to win support from the large population of Hispanics, an estimated 8.3 million people.

* Democrats will send 228 delegates to the national convention in August, the biggest single bloc remaining. Two-thirds of them are granted based on popular vote and one-third based on the outcome of caucuses held after the polls close on Tuesday.

* It's the second most populous U.S. state after California, with the third-largest state economy. Leading industries are trade, real estate and oil and gas.

* Conservatives have dominated both political parties in Texas in recent years, and national security issues are key to voters. All the candidates have touted their foreign policy credentials in the run-up to Tuesday's vote.

OHIO