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

* Another hotly contested state for the Democrats, considered a must-win for Clinton. McCain hopes to win the state to pull closer to clinching the Republican nomination.

* Polls close at 0030 GMT. Both Republican and Democratic contests are open to independent voters.

* White working-class voters make up a large share of Ohio's electorate where the focus is on the economy. The state has lost 23 percent of its manufacturing jobs since 2000 and the subprime mortgage crisis has hit hard, with foreclosures climbing 88 percent last year.

* Trade issues and healthcare have been at the forefront of the campaign, especially among Democrats in a state with a high percentage of labour union members.

* Ohio has been a swing state in presidential races, narrowly handing President George W. Bush a re-election victory in November 2004. Democrats picked up a number of statewide offices in 2006, including governor and a U.S. Senate seat.

VERMONT

* Polls close at midnight GMT. Voters do not need to register as Republicans or Democrats to participate in either party's primary.

* The state is known for its liberal politics, with Vermont attracting educated liberals willing to pay relatively high taxes to live in a pristine setting.

RHODE ISLAND

* Polls close at 0200 GMT. Independents can vote in either the Republican or Democratic contest.

* The smallest of the 50 U.S. states, it has been one of the most Democratic states in the nation since the 1930s. Politically moderate Republicans have also fared well in the state.

(Reporting by Deborah Charles, editing by Howard Goller)