(Reuters) - Greek Prime Minister Antonis Samaras faces a vote in parliament on Monday that will decide whether the country goes to snap elections that could bring the leftwing Syriza party to power and derail an international bailout.

In the most hotly contested vote for president since Greece joined the euro more than a decade ago, the result in the final round of voting is likely to be decided by a small handful of deputies.

If lawmakers fail to elect a successor to 85-year-old Karolos Papoulias, a snap election will be held within weeks. Syriza, leading in the opinion polls, vowed again to renegotiate the joint European Union-IMF bailout Greece needs to pay its bills and roll over its debt.

Syriza leader Alexis Tsipras said he had growing support in other countries struggling in the crisis.

"In Europe, sentiment is changing. Everyone is getting used to the idea that Syriza will be the government and that new negotiations will begin," he wrote in his party newspaper on Sunday.

With financial markets watching closely, former European Commissioner Stavros Dimas, the only candidate in the race, will need 180 votes to be elected. In the previous round of voting, he secured 168 votes, 12 short of the supermajority required.

Greek bond yields spiked sharply earlier this month after Samaras first announced that he was bringing forward the vote for president by two months in a bid to shore up support for his conservative/center-left coalition.

Voting is due to start at midday (0600 ET), with the result likely around an hour later.

Spyros Lykoudis, an independent who voted with the government in the second round before Christmas, said he was not optimistic that the parties would overcome their differences.

"Unless there is a surprise, unless a party changes its stance, I don't expect parliament to elect a president tomorrow given the current circumstances," he told Reuters.

"Nothing can be ruled out, but parties are in any case preparing for elections."

Samaras, who spent much of Sunday following the dramatic rescue of hundreds of passengers from a burning ferry, has appealed to parliament to support his nominee.

But having offered a deal to bring forward elections scheduled for mid 2016 to the end of next year, he ruled out new concessions to the opposition parties and independents expected to hold the key to the result.

Recent polls have shown Syriza has kept its lead over the ruling centre-right New Democracy party but the advantage has narrowed steadily over the past few weeks and Samaras said on Saturday he was confident of winning any election.

A poll on Saturday by the Alco institute showed Syriza leading New Democracy by 3.3 points, a slightly narrower lead than in the previous poll. It put support for Syriza at 28.3 percent and for New Democracy at 25 percent.

However, the outlook is complicated by the weakness of other parties. Samaras' coalition partner PASOK faces severe internal tensions and may split and fail to enter parliament, thus hindering the formation of a stable coalition majority.