* PM Robert Fico, political novice Andrej Kiska square off
* Some voters fear Fico's party would get too powerful
* His party would nominate new prime minister if he wins
By Jan Lopatka
PRAGUE, March 15 Slovaks vote on Saturday to pick a new president in an election that will either cement Prime Minister Robert Fico's power in the central European country or usher in an independent.
A Fico victory would give his centre-left Smer party full control of all the main power centres, even if the Slovak constitution does not grant the president himself a huge political role.
Fico, 49, took Slovakia into the euro zone in 2009 and has kept the country of 5.5 million friendly to investors despite levying extra taxes on banks and utilities.
But the prospect of him further consolidating power - Smer already has a parliamentary majority and enjoys one-party government - worries those Slovaks who would like to see checks and balances to counter corruption and give more independence to the justice system.
This gives a fighting chance to Andrej Kiska, a businessman-turned-philanthropist whose chances to beat Fico have grown in the latest opinion polls.
Analysts say Fico, still the favourite, leading by 9-15 points in most opinion polls in the past weeks, would be tempted to increase the powers of the president if he wins.
"He is a man of unlimited ambition," said political analyst Grigorij Meseznikov. "If he has the strength in parliament, the next day he will want to change the constitution (to get more powers)."
The president already has the power to name or approve some of the main figures in prosecution and judiciary. This has led to some political clashes in the past.
Rule of law is a key concern for investors in the country that has lured big foreign manufacturers including carmakers Kia and Volkswagen.
Kiska, 51, made millions of dollars in consumer credit companies which he sold a decade ago, setting up a charity to help families with ill children.
Saturday's first round is unlikely to produce an outright winner, who would need over 50 percent of the vote, but should send Fico and Kiska into a run-off on March 29.
Polling stations will open at 7 a.m. (0600 GMT) and close at 10 p.m. (2100 GMT). Results are expected overnight.
Slovak voters have shown they can unite behind an underdog. Outgoing president Ivan Gasparovic was elected for the first of two five-year terms in 2004 because voters united against former authoritarian prime minister Vladimir Meciar.
Other candidates in Saturday's vote - a handful of politicians from the fragmented centre-right opposition - lag Kiska by a double-digit margin and Fico by at least 20 points.
Fico would have to give up his post of prime minister if he wins, but his Smer party holds a majority in parliament and would simply replace the former lawyer with another Smer nominee.
A possible choice is Robert Kalinak, the interior minister in the current cabinet and a longtime member of the party that Fico founded. (Editing by Robin Pomeroy)