FACTBOX-Key facts about Venezuela's state elections

Nov 19 (Reuters) - Venezuelans vote on Sunday in nationwide elections for governors and mayors in 22 states that will test support for President Hugo Chavez's left-wing reforms in one of the United States' most important oil suppliers.

U.S.critic Chavez's Socialist Party is expected to hold most states and cities but may lose a handful of posts as voters reject crime, corruption and inefficiency.

Bigger losses would be a blow to Chavez, who wants to convince Venezuelans to back a constitutional reform that would let him run for re-election in 2012.

Here are some facts about Venezuela's electoral map:

* Venezuelans will vote for governors and mayors in 22 states, plus the federal district of Caracas. Only the vast and sparsely populated jungle state of Amazonas will not take part, because of a previous electoral conflict.

* The most important races are in the capital Caracas, the densely populated, oil-producing state of Zulia and the coastal state of Miranda that includes swathes of the capital's metropolitan area.

* Zulia is currently governed by Chavez's main opposition rival Manuel Rosales, who came a distant second in a 2006 presidential vote. Chavez calls Rosales a money launderer involved in assassination plots and has called for his arrest. Rosales is now running for mayor of Zulia's capital Maracaibo. The current mayor, a Chavez loyalist, is in a tight race to take the governorship from a Rosales ally.

* Miranda is governed by one of Chavez's closest aides and ex-vice president, Diosdado Cabello, who is up for re-election. He faces a serious challenge from an ambitious young politician, Henrique Capriles, but is expected to hold the state.

* The election in Caracas pits one aging former mayor of the capital against another. Aristobulo Isturiz led street protests that restored Chavez to power after a 2002 coup against him. His rival, Antonio Ledezma, is a hard-line anti-Chavez politician who has boycotted elections in the past. The vote is likely to favor Chavez, especially after the opposition's leading candidate for the post was disqualified over corruption charges in a move condemned by rights groups.

* Chavez's older brother could lose the family's home state of Barinas, currently governed by his father. The loss would be a symbolic blow for Chavez, who has promised public works including an international airport for the vast ranching state.

Accusations of corruption have swirled around Chavez's relatives in the state, but have not yet been seriously investigated.

* Another populous state, Carabobo, has turned into a battleground where a colorful former late-night talk show host and "Chavista" accuses his rival, a dissident former Chavez ally, of links to cocaine traffickers.

Chavez has threatened to call tanks into the streets if the opposition wins the state. (Reporting by Frank Jack Daniel; Editing by Saul Hudson and Xavier Briand)