(Adds Maduro quote, paragraph 6, details)

By Andrew Cawthorne and Leon Wietfeld

CARACAS, Dec 10 (Reuters) - Venezuelans voted on Sunday in mayoral races that the ruling Socialist Party looked likely to sweep, deepening opposition divisions and consolidating President Nicolas Maduro's position ahead of a likely 2018 re-election campaign.

Major opposition parties boycotted the polls for 335 municipal mayors across the South American nation of 30 million people, protesting a system they say serves Maduro's "dictatorship."

But some small parties in the Democratic Unity coalition dissented and ran candidates, confusing opposition supporters already disillusioned at the failure to weaken Maduro in months of protests that took 125 lives earlier this year.

Under his rule since 2013, Venezuela has endured one of the most profound economic meltdowns in Latin American history.

"If we're going to change the government, we need to do it democratically," said 81-year-old retiree Raul Ocana. "It was a huge mistake (by opposition parties) not to participate."

After the Socialists notched surprise wins in October gubernatorial elections, the government urged supporters to repeat the feat on Sunday to increase the party's current share of roughly 70 percent of mayorships.

"If you want to know what democracy is, come to Venezuela," said a buoyant Maduro, casting his vote in Caracas.

State agencies have pressured voters to participate in elections this year, particularly in the July 30 vote for the all-powerful Constituent Assembly, which the opposition also boycotted.

Some government employees said on Sunday they were being flooded with text messages urging them to show they had voted by posting their ID numbers to state-run websites and to upload pictures of voting centers to social networks.

"They won't leave us alone," said a government ministry employee who requested anonymity. "It's worse than ever."

Opposition activists said the government abused state resources, including bribing people to vote with handouts of food vouchers worth 500,000 bolivars - more than a monthly minimum wage or about $5 at the black market wage.

Voting lines observed by Reuters reporters around Venezuela appeared much thinner, however, than at past elections.

'ABSTENTIONISTS WILL REGRET IT'

The Socialists were also hoping to win a rerun of the October gubernatorial election in western Zulia state.

Opposition leader Juan Pablo Guanipa won that governorship in October, but the election was annulled and he was barred from holding office after he refused to swear allegiance to the pro-Maduro legislative superbody.

Former Zulia Governor Manuel Rosales ran on the opposition ticket, but Guanipa supporters and other sectors of the opposition boycotting Sunday's vote have called him a "traitor."

Yon Goicoechea, an opposition activist running for mayor in the wealthy Caracas suburb of El Hatillo, said it was self-destructive for larger anti-Maduro parties to abstain and hand political victories to the Socialist Party.

"There's reticence to participate because the national election board doesn't offer guarantees or impartiality," Goicoechea, who is just out of jail for alleged coup-plotting, told Reuters. "But the solution cannot be giving up the right to vote.... The abstentionists will regret it within two weeks."

Maduro's approval ratings have fallen by half since he was elected in 2013 following the death of late Socialist leader Hugo Chavez, his mentor and predecessor.

Despite the nation's economic problems and the accusations of squashing democracy, Maduro is enjoying a political upturn after the October gubernatorial vote.

He is expected to be the Socialists' candidate in the 2018 presidential election and maintains support among party loyalists like retiree Jose Flores, 71.

"I'm voting for democracy - it's a way of showing other countries that there's no dictatorship here," Flores said outside a voting center on the poor west side of Caracas. "On the contrary, what we have is peace and democracy." (Additional reporting by Johnny Carvajal and Deisy Buitrago in Caracas; Maria Ramirez in Puerto Ordaz; Anggy Polanco in San Cristobal; Tibisay Romero in Valencia and; Mircely Guanipa in Paraguana; Editing by Lisa Von Ahn and Peter Cooney)