Spain's increasingly desperate struggle to put its finances right has seen its borrowing costs soar to levels that are not manageable indefinitely, reflecting a growing belief that it will need a sovereign bailout the euro zone can barely afford.

It has become the recent focus for investors, but Greece - where the sovereign debt crisis began - remains a powder keg. If Athens were to default or exit the euro zone, the knock-on effects could push Spain and even Italy over the edge.

With inspectors from the EU, European Central Bank and International Monetary Fund returning to Greece to decide whether to keep it hooked up to a 130-billion-euro lifeline or let it go bust, three EU officials said they were likely to conclude Athens cannot repay what it owes, making a further debt restructuring necessary.

This time, the European Central Bank and euro zone governments would likely have to take a hit on some of the estimated 200 billion euros ($240 billion) of Greek government debt they own if Athens is to be put back on a sustainable footing.

But there is no willingness among member states or the ECB to take such dramatic action at this stage.

"Greece is hugely off track," one of the officials told Reuters, speaking on condition of anonymity. "The debt-sustainability analysis will be pretty terrible."

Prime Minister Antonis Samaras said Greece's economy could contract by more than 7 percent this year, pushing debt-cutting targets further out of reach, but he pledged to stay the course.

"There are certainly delays in this year's agreed program, and we must quickly catch up," Samaras told party colleagues. "Let's not kid ourselves, there is still big waste in the public sector, and it must stop."

Underlining the pressure on the euro zone, Moody's Investor Service lowered the outlook on the EU's temporary bailout fund, the European Financial Stability Facility (EFSF), after threatening the top-notch credit rating of three of its main backers, including Germany, earlier in the week.

The Spanish Treasury sold the 3 billion euros of three- and six-month bills it was aiming to, though yields climbed; the six-month paper jumped to 3.691 percent from 3.237 percent last month.

"The most important takeaway from this auction is that Spain was able to get all its debt out the door," said Nicholas Spiro of Spiro Sovereign Strategies. "Still, in March, Spain was able to issue six-month debt at a yield of under 1 percent. Now it is paying 3.7 percent."

Spain had cushioned itself by securing well over half its annual debt needs in the first six months of the year when market conditions were more benign, but that advantage has evaporated as its funding needs for the rest of the year have grown.

On Friday, the government said it expected the economy to remain in recession well into next year, while the autonomous region of Valencia became the first to ask Madrid for aid to pay debt obligations it cannot meet. Others are expected to follow.

Spain's northeastern region of Catalonia, responsible for a fifth of the country's economic output, admitted it had financing needs to meet while its access to markets was shut, but had not decided yet whether to tap a state liquidity line.

BOND MARKET MESSAGE

On the secondary market, Spanish five-year government bond yields rose above 10-year yields for the first time since June 2001. Having to pay more to borrow shorter-term rather than longer-term is usually a sign that markets think the risk of a default or debt restructuring has increased.

"The spread between 5- and 10-years moved to negative today, which is a classic sign that the market thinks the current trends are unsustainable for Spain's fiscal dynamics," said Nick Stamenkovic, bond strategist at RIA Capital Markets.

The return investors demand to hold Spanish 10-year bonds is now at 7.6 percent, while the cost of insuring Spanish debt against default has also hit record highs.

Ten-year yields above 7 percent have proved to be a tipping point leading eventually to bailouts for other countries in the euro zone, though Spanish Economy Minister Luis de Guindos insisted on Monday that Madrid would not need more aid.

The government has already asked for up to 100 billion euros to recapitalize the nation's banks, which have been battered by a four year economic downturn and a property crash.

The government has launched a fresh 65 billion euro package of tax rises and spending cuts designed to chip away at its debt mountain but it will also probably drive the economy deeper into recession.

The alarming spiral of Spain's debt costs has banished any hopes that a bailout of its banks, or a June EU summit that gave the euro zone's rescue funds a green light to intervene in the markets, has put the debt crisis into abeyance.

Spain and Italy have called for help to ward off market pressure. The ECB has cut interest rates but has shown marked reluctance to revive its bond-buying program, the only mechanism that could lower borrowing costs at a stroke.

De Guindos and Wolfgang Schaeuble, Spain and Germany's Finance Ministers, called on Tuesday for a quick implementation of the decisions of the last European Union summit, particularly setting up a banking union with a single European supervisor.

They also said after meeting in Berlin that Spain's funding costs did not reflect the fundamentals of its economy and the sustainability of its debt.

French Foreign Minister Laurent Fabius said further aid for Spain could take the form of an increase in Europe's rescue fund or action by the ECB.

"I hope it will not be necessary to intervene again," he told France 2 television. "If we have to intervene, it could be an increase in the firewalls ... or interventions by the central bank."

The euro zone as a whole is now subsiding into recession.

Business surveys on Tuesday showed the currency area's private sector shrank for a sixth month in July, with the downturn that began in the euro zone's high debt nations now becoming entrenched in Germany and France.

Moody's lowered the outlook on the EFSF's provisional(P)Aaa long-term rating to negative from stable, in a move it said followed from its decision earlier in the week to change the outlooks for Germany, the Netherlands and Luxembourg to negative.

The ratings agency cited an increased chance that Greece could leave the euro zone when in lowered the outlook on all the fund's top-rated guarantors except Finland.

It also warned Germany and the other 'AAA'-rated countries that they might have to increase support for Spain and Italy.

($1 = 0.8275 euros)

(Additional reporting by Paul Day, Jan Strupczewski, Ilona Wissenbach, Annika Breidthardt, Manuel Ruiz, Dina Kyriakidou, Nicholas Vinocur, Marius Zaharia, Emelia Sithole-Matarise and Ana da Costa; Writing by Mike Peacock; Editing by Anna Willard, Janet McBride, Will Waterman and Alex Richardson)

• A Permanent Economic Emergency