By George Georgiopoulos
ATHENS (Reuters) - Greek Prime Minister Antonis Samaras called for support on Wednesday ahead of a tight parliamentary vote that will trigger elections unless he can win backing from independents and smaller parties that have so far rejected helping his coalition.
As the vote neared, Evangelos Venizelos, the leader of centre-left coalition partner PASOK, said he was ready to hold discussions with opposition parties over possible concessions but said his party was ready to go to the polls if needed.
"We are ready for elections but up until the last minute...we will keep hoping that a sense of responsibility prevails," Venizelos told PASOK lawmakers.
He repeated an offer to opposition parties of a seat at the negotiating table with Greece's international creditors and said "we are open to discussing everything, because what we care about is the national interest".
Two key small parties -- Democratic Left, which quit the government last year, and the right-wing, anti-austerity Independent Greeks -- repeated that they would not vote with the government and would prefer a snap election.
The 300 lawmakers in parliament begin the first of three votes to elect a new president at 7.00 p.m. (1700 GMT).
The government is not expected to win Wednesday's vote or a second ballot on Dec. 23, when it would have to secure 200 votes to win but voting will be closely watched as a sign of momentum before a deciding final round on Dec. 29, when the required super majority drops to 180.
"If we can manage to get over 160 in favour of our candidate (on Wednesday), it will be a positive first step," Defence Minister Nikos Dendias told Star TV.
Samaras, whose conservative/centre-left coalition has 155 deputies in parliament, must secure at least 25 votes from the smaller parties and independents for the super majority needed to elect his candidate Stavros Dimas in the final round.
The prime minister's office issued a statement saying the vote was not about his government but about defending the constitution and respecting the office of president.
"It is also to avoid a political adventure that could prove fatal for the country's European course," it said.
The head of state is a largely ceremonial post. But failure to elect a president with a three-fifths majority in parliament triggers early elections, which polls show would probably be won by the radical leftist Syriza party that promises to axe the bailout programme Greece depends on to keep afloat.
Greece's euro zone partners are wary that such a result could trigger trouble in the currency bloc, although it is political fallout rather than financial that is foremost on their minds.
BATTLE FOR VOTES
Both sides in parliament are battling to win over a pool of about two dozen independent lawmakers whose votes will decide the outcome. Of these, seven have said they will support Samaras and eight have declared against, at least in the initial rounds.
As manoeuvring continued, speculation grew over possible alternative proposals, including a deal that could involve a commitment by the government to hold elections later next year in exchange for support in the presidential vote.
A group of at least eight independent and centre-left lawmakers proposed backing a consensus presidential candidate as long as national elections are called in 2015.
In addition to the independents, Samaras would also need the support of at least a few lawmakers from Democratic Left, which has 10 deputies and the Independent Greeks, both of whom reiterated they would vote against the government in all three rounds.
Underlining the drama of the occasion, seven lawmakers from the far-right Golden Dawn party currently in jail pending trial on charges of being members of a criminal association, will be allowed to attend parliament to vote.
Fears of a new chapter of prolonged political uncertainty have sent Greek stocks and bonds crashing since Samaras last week announced the presidential vote would be held this month instead of February. Greek stocks fell over 20 percent in three days last week while 10-year bond yields leapt over 9 percent.
Samaras has warned of a "catastrophic" return to the height of Greece's debt crisis - when it risked being driven out of the euro zone -- if his government falls, while Syriza has accused him of scare-mongering and blackmail to win support.
(Additional reporting by George Georgiopoulos and Lefteris Papadimas; Writing by Deepa Babington and James Mackenzie Editing by Ralph Boulton)