Greece's leaders battled to salvage a 130-billion-euro (108 billion pounds) EU/IMF bailout on Wednesday, rejecting criticism of their commitment to a punishing austerity package despite staunch opposition to it among voters.

But with mistrust of Athens high, EU sources told Reuters euro zone finance officials were studying whether it was possible to delay part or all of the rescue deal while still avoiding a disorderly default - news which pushed German Bund futures to session highs.

Finance Minister Evangelos Venizelos insisted that Greece would clarify all outstanding issues on a 3.3-billion-euro package of cuts and attacked critics for playing with fire.

After a three-hour conference call among the 17 euro zone ministers to discuss how to proceed, Eurogroup chairman Jean-Claude Juncker issued a statement saying progress had been , but provided few details.

He said the European Central Bank, IMF and European Commission had completed a report into Greece's debt sustainability - a precondition for approving the bailout - and that he expected the Eurogroup to be able to take the necessary decisions on Athens at the next meeting on Monday.

Further considerations are necessary regarding the specific mechanisms to strengthen the surveillance of programme implementation and to ensure that priority is given to debt servicing, he said.

On the basis of the elements that are currently on the table and the above-mentioned additional input, I am confident that the Eurogroup will be able to take all the necessary decisions on Monday 20 February.

One of the outstanding issues had been a written commitment from Antonis Samaras, the leader of Greece's opposition conservative party, that he will stick to the agreed programme if he wins elections expected in April.

Samaras, who is ahead in the polls and widely tipped to be Greece's next leader, delivered that letter on Wednesday.

If New Democracy wins the next election in Greece, we will remain committed to the programme's objectives, targets and key policies, Samaras wrote.

But he insisted the fast-shrinking Greek economy must also be kickstarted into life and reserved the right to adapt details of the package accordingly - a hedge that could prove a sticking point for increasingly frustrated euro zone partners.

Prioritising recovery along with the other objectives will only make the programme more effective and the adjustment effort more successful. Therefore ... policy modifications might be required to guarantee the full programme's implementation, he wrote.

Greece has said it must initiate a debt swap deal with private sector bondholders by Friday to meet a March 20 deadline for 14.5 billion euros in debt repayments. It was hoping to have the euro zone's backing for its second bailout this week. If that backing comes on Monday, it's possible the debt swap could now start in the middle of next week.

STRONG DOUBTS

EU sources said some in the euro zone doubted the commitment of Greece's leaders to austerity, and queried whether it would be enough to bring Greece's debt-to-GDP ratio down from 160 percent now to a target of 120 percent by 2020.

There are proposals to delay the Greek package or to split it, so that an immediate default is avoided, but not everything is committed to, one official briefed on preparations for a euro zone finance ministers call later in the day told Reuters.

They'll discuss the options, he said, adding: There is pressure from several countries to hold off until there is a concrete commitment from Greece, which may not come until after they've held elections. [ID:nL5E8DF2K2]

Samaras' belated commitment to honour the austerity plan may put that plan on the back burner, even if concerns linger.

The euro fell to its lowest in more than a week against the dollar and March Bund futures rose by as much as 60 ticks on the day to 139.12 after the Reuters report.

With every small piece of news that we get from Athens, the situation is becoming better, said an EU diplomat. Whether it will hold all the way through, we can't know.

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PLAYING WITH FIRE

Venizelos earlier insisted there were only a few remaining issues to be resolved on the package of wage, pension and public sector job cuts lashed out at Greece's doubters.

There are now powers in Europe who are obviously playing with fire because they believe ... that not all requirements will be met, and who may even want Greece out of the euro zone, he told reporters in Athens.

Rioters torched buildings across Athens late on Sunday as Greek lawmakers passed the austerity bill, of which around 325 million euros of cuts still need to be identified.

But after a series of broken promises since Athens was first bailed out in May 2010, trust is in short supply.

When you look at the internal political discussions in Greece and the opinion polls, then you have to ask who will really guarantee after the elections ... that Greece will stand by what we are now agreeing with Greece, German Finance Minister Wolfgang Schaeuble told SWR2 radio.

Greece's President Karolos Papoulias, who holds a largely ceremonial role, fought back, saying in a speech:

Who is Mr Schaeuble to insult Greece? Who are the Dutch? Who are the Finnish?

European Central Bank board member Joerg Asmussen said approval by the Eurogroup at regular talks next Monday would allow a sovereign debt swap to be completed in time.

If the Eurogroup (of euro zone finance ministers) is able to make a positive political decision next Monday, the bond swap with voluntary PSI (private sector involvement) can immediately begin and be completed in time, he told Reuters.

Greece is well on its way to suffering one of the biggest slumps of modern history. Output has contracted 16 percent from its peak in 2008 and the cuts will inevitably make that worse.

Prime Minister Lucas Papademos has said that failure to back the bailout would consign Greece to economic catastrophe.

But with many Greeks suffering huge cuts in their living standards and young people burning and wrecking almost 100 Athens buildings in one night on Sunday, some people believe the catastrophe is already under way.

(Additional reporting Harry Papachristou and Lefteris Papadimas in Athens, and bureaus in Paris, London, Brussels and Berlin; Writing by Mark John)