Polls show the 47-year-old lawyer could win 40 percent of the vote, potentially knocking his reformist rival Mikulas Dzurinda's centre-right SDKU out of power and possibly out of parliament.

A government led by Fico's pro-European Smer party would assuage Slovakia's euro zone partners who were upset by the outgoing coalition's refusal to contribute to the first bailout of Greece and holding up strengthening of a euro zone rescue fund.

Many centre-right voters, disillusioned by political corruption scandals, are expected to stay away from the ballot box and polls show turnout may fall to a record low of 44 percent, which would help Fico.

Voting started at 0600 GMT and will end at 2100 GMT.

"I still don't know. I would like to vote for centre-right parties but I'm still not decided. There were many scandals, they have stolen the entire country, and that's not good," said Tomas Rigel, 35.

The unrivalled leader of centre-left Smer, Fico says he plans to use tax hikes to maintain welfare and cut the budget deficit, and continue the outgoing cabinet's effort to protect the country's sovereign credit ratings.

Fico, who served one term as the central European country's prime minister in 2006-2010, has pledged to dump Dzurinda's flagship reform - a 19 percent flat income tax - and reel in more from the rich, banks and other firms.

SUPPORT

His plans involve almost doubling a special tax on bank deposits to 0.7 percent, raising the corporate tax to 22 percent, from 19 percent now, and raising the income tax for people earning over 33,000 euros per year.

"If you have record profits, you will pay record taxes," Fico has told election rally crowds.

He has also criticised labour reforms under the previous centre-right government that have made it easier to hire and fire workers, striking a chord among voters afraid of job insecurity.

Rhetoric aimed at poorer, older, and rural voters has served him well in the euro zone's second-poorest country, where 13.7 percent are out of a job.

The minimum Slovak monthly salary is just 327 euros ($430), half of the minimum pay in crisis-hit Greece.

The election comes two years early, after an SDKU-led coalition government collapsed in acrimony last October when one of its junior members, the free-market SaS party, refused to back the expansion of the euro zone's bailout fund.

At the heart of the SDKU's likely electoral rout, however, lies the leaking of a secret service file in December purporting to detail bugged conversations between top politicians and businessmen in which they allegedly discuss kickbacks in return for the sale of public companies in the mid-2000s.

Details of the file, code named "Gorilla", have drawn tens of thousands of outraged Slovaks onto the streets in the past month in a rare display of public anger.

On Friday, police used teargas to disperse a demonstration of around 200 people at the government's offices who threw eggs and shouted "Put the gorilla behind bars".

Police said several protesters were detained.

Dzurinda and other SDKU officials have strenuously denied any allegations of corruption in the file.

"The campaign has been about what has been wrong with Slovakia since its birth. What is bothering us is mainly, apart from a high jobless rate and social issues, corruption," Jan Baranek, a political analyst at Polis Slovakia, said.

The "Gorilla" scandal has marred an otherwise successful track record for Dzurinda, a former prime minister who led Slovakia into NATO, the European Union and paved the way for euro adoption in 2009.

Fico has pledged to form a coalition with one of the four main parties from the fragmented centre right, with the conservative Christian Democrats (KDH) a prime candidate.

But political pundits said if Smer won a full majority in the 150-seat house, he would be likely to end up ruling alone.

Copyright Reuters, 2012