European Union finance ministers on Sunday promised to counter the wolfpack of the financial markets as they sought agreement on a 600 billion euro ($805 billion) plan to keep Greece's debt crisis from spreading.

The compromise measure under discussion included loan guarantees by euro zone countries worth 440 billion euros, a 60 billion euro stabilization fund and a 100 billion euro top-up of International Monetary Fund loans, EU sources said.

Financial markets have been punishing heavily indebted euro zone members, threatening to plunge them into Greece's plight. The safety net being assembled was meant to protect other countries with bloated budgets, such as Portugal, Spain and Ireland.

Jitters over euro zone finances have set global markets on edge, and provided a backdrop for a nearly 1,000-point drop in the Dow Jones industrial average on Thursday, whose trigger remains a mystery.

Hopes the EU package would successfully tackle the crisis helped lift the euro, which gained almost 2 percent against the U.S. dollar and 3 percent on the yen in early Asia trade. U.S. stock futures also surged at the start of trade on Sunday.

Moving swiftly to bolster Greece and instill some confidence in shaky markets, the IMF approved a 30 billion euro rescue loan as part of a broader combined EU-IMF bailout for the country totaling 110 billion euros. The IMF said 5.5 billion euros from the three-year loan would be disbursed immediately.

To secure the funds, Greece has committed to budget-cutting measures so sharp that they have already caused violent protests.

Today's strong action by the IMF to support Greece will contribute to the broad international effort underway to help bring stability to the euro area and secure recovery in the global economy, IMF Managing Director Dominique Strauss-Kahn said in a statement.

'WOLFPACK BEHAVIORS'

But whether the coordinated international actions would settle global markets, which have been roiled in recent days, remained to be seen. Policymakers around the globe have become worried about the knock-on effects should the crisis spread.

We now see ... wolfpack behaviors, and if we will not stop these packs, even if it is self-inflicted weakness, they will tear the weaker countries apart, Swedish Finance Minister Anders Borg told reporters in Brussels as he arrived for the EU meeting.

Britain's finance minister Alistair Darling stressed the need to stabilize markets, while ministers from France, Spain, Finland and other euro zone states vowed to defend their shared currency.

U.S. President Barack Obama and German Chancellor Angela Merkel spoke by phone earlier on Sunday about the importance of EU members acting to build confidence in markets.

Economists estimate that if Portugal, Ireland and Spain -- three other heavily indebted euro zone countries -- eventually come to require bailouts similar to Greece's, the total cost could be some 500 billion euros.

As details of the financial barriers that the EU was putting up to ward off speculators against Greece and other debt-laden countries became public, G20 finance officials held a teleconference to discuss the crisis.

Last week, fears that a euro zone debt crisis could rock banks and the global economy like the September 2008 collapse of U.S. bank Lehman Brothers swept through markets, pushing global stocks to near a three-month low. It was unclear whether the EU crisis package would stem the tide.

All in all this is good news, but it is unlikely in itself to calm markets; it's all too 'slow-burner' stuff, said Erik Nielsen, chief European economist at Goldman Sachs. He said he expected the European Central Bank would soon need to take some type of emergency action.

EU sources said ECB governors met to discuss the crisis, but no details were available.

MARKET TURMOIL

The 16 nations that use the single currency have been criticized for contributing to market uncertainty by responding too slowly to the crisis in Greece.

An IMF board source told Reuters that some board members had shared those concerns and raised worries that the crisis could spread to other euro zone countries.

A euro zone summit last week asked for a European stabilization mechanism.

Some economists said the move was welcome, but that it would cure the symptoms, rather than the disease.

By putting in place additional safeguards for the euro area financial system, governments finally appear to be rising to the challenge of the sovereign debt crisis, Morgan Stanley said in a research note to clients.

But, like the measures taken before -- for the benefit of Greece -- a stabilization fund is just buying time for distressed borrowers, it said.

(Additional reporting by Jan Strupczewski, John O'Donnell and David Brunnstrom in Brussels and Lesley Wroughton in Washington; writing by Charles Dick and Tim Ahmann; editing by Mohammad Zargham)

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