Greek Prime Minister Lucas Papademos faces a critical task of convincing international lenders and political party leaders on Sunday to agree to the stringent terms of a 130 billion euro ($171 billion) rescue plan to stave off looming default.

Greece on Saturday warned it had just one day left to clinch the bailout plan with political leaders and impatient lenders who accuse it of dragging its feet on promised reforms.

There is great impatience and great pressure not only from the three institutions that make up the troika but also from euro zone member states, said Finance Minister Evangelos Venizelos on Saturday after what he called a very difficult conference call with euro zone counterparts.

The moment is very crucial. Everything should be concluded by tomorrow night.

Papademos, who failed to resolve all issues in talks with lenders on Saturday, is due to call in the socialist, conservative and far-right party leaders in his coalition on Sunday to seek their blessing for reforms in the bailout.

Athens has wrangled without success for weeks with lenders and private bondholders on the bailout package and a debt restructuring plan, putting itself dangerously close to bankruptcy as 14.5 billion euros of debt falls due in mid-March.

In an apparent warning to Greek political leaders opposing key reforms, Venizelos said the patience of European partners and the International Monetary Fund (IMF) footing the bill for Greece's bailout was wearing thin.

Euro zone finance ministers told Greece on Saturday it could not go ahead with an agreed deal to restructure privately held debt until it guaranteed it would implement reforms needed to secure a second financing package from the euro zone and the IMF.

STICKING POINTS

Venizelos said Athens had made progress by agreeing a plan to recapitalize Greek banks and details on privatization. A senior banker told Reuters the recapitalization would occur mainly via common shares with restricted voting rights.

But far bigger sticking points on wages and spending cuts remain unresolved, and Venizelos warned that the stakes were rising as time ran out.

We are on a knife-edge, he told reporters. The distance between the successful completion of the procedures and an impasse which could happen by accident or because of a misunderstanding is very small.

Euro zone officials said ministers had bluntly said they would not sign off on a planned debt swap until Athens guaranteed it would implement promised reforms.

There was a very clear message ... to the Greeks that enough is enough, one euro zone official said. There is a great sense of frustration that they are dragging their feet.

Athens' talks with its international lenders have stumbled over their demands, which include cutting labor costs by axing holiday bonuses and lowering the minimum wage - proposals vehemently opposed by Greek political party chiefs.

Greek officials have described the negotiations as tough, with the troika of European Central Bank, European Union and IMF lenders unwilling to yield an inch from their demands.

The talks have moved slowly also because the troika wants agreement on all parts of the complex Greek rescue deal -- including any contribution by public creditors like the ECB -- before approving the bailout, a source close to the talks said.

Athens also wants public creditors like the ECB to take part in the bond swap deal, under which banks and insurers will take real losses of about 70 percent on the Greek debt they hold in a bid to ease Greece's debt burden by 100 billion euros.

The bond swap talks were now the easier part of the overall process to save Greece, said Venizelos. Representatives for the banks and insurers were expected to continue talks in Athens over the weekend.

The debt swap and bailout was designed to bring Greece's debt down to the targeted 120 pct of GDP level by 2020, but with Greece's economic prospects deteriorating, fears have grown that European partners will need to stump up more money.

EU sources say euro zone governments may now have to cough up an extra 15 billion euros on top of the 130 billion already agreed.

The lenders have demanded extra spending cuts worth about 1 percent of GDP - or just above 2 billion euros - this year, including big cuts in defense and health spending.

They also want all Greek political leaders - who are keen not to be linked directly with the painful reforms as they gear up for elections expected in April - to endorse the measures, irrespective of the outcome at the polls.

In the latest sign that coaxing political leaders into backing the reforms will be anything but easy, the leader of the far-right LAOS party, George Karatzaferis, rejected Venizelos' ultimatum to strike a deal by Sunday.

(Additional reporting by Angeliki Koutantou and Ingrid Melander in Athens, Jan Strupczewski in Brussels,; Writing by Deepa Babington; Editing by Sophie Hares)

International Monetary Fund