By Renee Maltezou and John Stonestreet
ATHENS (Reuters) - Greece's two political heavyweights will have undecided voters in their sights on Monday in a final televised head-to-head debate before national elections, both seeking the elusive soundbite that might break a deadlock in opinion polls.
With Sunday's ballot looming, the leftist Syriza party of former prime minister Alexis Tsipras and the New Democracy conservatives led by Vangelis Meimarakis have been stuck in the same place in the surveys for several weeks - virtually neck and neck and well short of parliamentary majority.
Their respective personal popularity ratings have also stagnated around or slightly below 45 percent.
Both men have so far given loyal voters little reason to switch allegiance, having devoted much of their campaigns to trading accusations over the country's ailing economy, institutionalized corruption and responses to the refugee crisis.
But voters yet to decide which party to back or intending to abstain altogether - up to a fifth of the electorate according to some polls - offer a clearer target.
"This debate is crucial mainly because of the big number of undecided voters and those who don't want to vote," Dimitris Mavros of pollsters MRB said. "The question is who will be more convincing."
Voted into office in January on an anti-austerity platform, Tsipras forced Sunday's election by resigning in August, trying to quell a rebellion in his party and win a stronger mandate to implement austerity measures under a 86 billion euro ($97.3 billion) bailout he initially opposed.
'MORE LIVELY' THIS TIME?
Neither he nor Meimarakis impressed commentators during a seven-party televised debate on Wednesday that many dismissed as a damp squib - but organizers are promising more drama this time.
"We made an effort to make it more lively," said a member of the all-party committee that decided the terms of Monday's debate, in which the leaders will fire questions at each other as well as facing them from reporters and the moderator.
Tsipras is expected to reiterate his claim that scandal-tainted New Democracy administrations helped bring about the current crisis, while Meimarakis will again accuse Syriza of crippling the economy, pollsters said.
Both men have said they are anxious to avoid a second round of elections, though the former prime minister insists Syriza will have enough support to govern without New Democracy, while Meimarakis has repeatedly talked up the possibility of a grand coalition.
Such an alliance "would go against nature", Tsipras told state ERT broadcaster on Sunday.
Chances of him winning Sunday's poll outright look slim.
The few polls this month that have taken account of undecided voters' preferences have also been unable to split the two parties, putting both on around 31 percent - still well short of the 36.3 percent that took Syriza into office in late January.
But Tsipras' insistence on rejecting a grand alliance could still prove decisive, pollsters say, citing evidence from weekend surveys that this drove a small swing in Syriza's favor, with Meimarakis' focus on a coalition making him appear weak.
Meimarakis recovered his poise during a news conference on Sunday, Mavros said.
"If he maintains that stance tonight, he may reverse the trend that we saw in polls over the weekend," the pollster said.
"Or Syriza may win it all tonight."
($1 = 0.8835 euros)
(Additional reporting by Michele Kambas Editing by Jeremy Gaunt)