Spain’s treasury minister said Tuesday that his country was being choked off from access to credit, sounding the country’s clearest call for help yet in the 21 / 2-year-old crisis that could leave one of Europe’s largest economies on life support.

Only three small euro-zone countries have resorted to international bailouts and the hard conditions that come with them, and Spain, the currency union’s fourth-largest economy, is desperate to avoid becoming by far the largest casualty.

Treasury Minister Cristobal Montoro called Tuesday for Europe to give his country’s faltering banks direct aid in a bid to prevent Spain’s financial system and the government’s finances from dragging each other down. Germany, which as Europe’s largest economy has de facto veto power over any new aid programs, opposes the idea even though it is floating major long-term plans to shore up Europe’s finances.

Panicked investors have pushed borrowing rates for Spain so high that “the market door is not open for Spain,” Montoro told Madrid’s Onda Cero radio Tuesday. “The risk premium says that as a state we have a problem in accessing markets.” Spain hopes to raise as much as $2.5 billion in a bond auction Thursday, suggesting that policymakers here think that the door is not fully shut.

Spain’s struggles could pose the largest challenge so far in a long-simmering crisis that has turned a once-booming confederation of European countries into a continent racked by recession, unemployment and financial uncertainty. Only Germany has pockets deep enough to push down countries’ borrowing costs, guarantee fearful depositors’ investments and kick-start listless economies, and German leaders have in recent days shown openness to a far-reaching bargain that would harness the might of its taxpayers to bolster its struggling neighbors.

The catch? The changes that Germany is considering would come only on a time scale of years, far too slow to help Spain with its pressing problems in the coming days and weeks. Estimates on how much the Spanish banking system would need range from $50 billion to $125 billion — Montoro said it was “not astronomical” — and a bailout of the entire country could cost far more.

But Germany has steadfastly opposed any attempt to channel the bailout funds straight to Spanish banks, saying that if Spain needs the funds, it should follow in the footsteps of the other troubled euro-zone economies that have needed to request national-level bailouts with all the strings attached.

“Our position is that everything is more or less in place in terms of immediate crisis response,” said an official at the German Finance Ministry, speaking under conventional ground rules of anonymity.

Still, broad measures — including giving bank deposits European-wide support, creating a strong regional banking regulator that could override national governments and pooling a portion of the debt of the 17 countries that use the euro — are being discussed in Europe to an extent unimaginable just months ago. But any new plans would probably come with a steep price: Countries would have to hand unprecedented control over sovereign decisions about borrowing and spending to the European Union.

In comments to Spain’s Senate, Prime Minister Mariano Rajoy echoed his treasury minister’s concern, saying, “Europe needs to decide where it is going to give security and state that the euro project is irreversible and not a game.” He called for medium-term efforts aimed at deeper economic integration, such as collective debt issued by the nations of the euro zone. But in comments that reflected Spain’s growing woes, he said Europe “needs to support those who are in difficulties.”

Redemption fund

The Spanish plea came just ahead of an emergency conference call in which top finance officials from the Group of 7 large economies discussed Europe’s response to its crisis.

German Chancellor Angela Merkel has worried that without pressure from markets, troubled countries would lack the will to take the painful steps that she thinks are necessary to fix their problems for good.

Merkel’s bargain, requiring her neighbors to turn over tremendous power to the E.U., may not be acceptable to France or Italy — both of which want faster fixes and to keep more sovereignty — or to Britain, which does not use the euro but whose consent is necessary for any E.U.-wide fixes.

On Monday, Merkel said she would be open to a European banking union that would shift regulatory control of major banks away from nations and over to the E.U., calling for “more Europe, not less Europe.” European Commission President Jose Manuel Barroso has said he wants Europe-wide deposit insurance to be part of that, too.

And Germany has shown new interest in a proposal for commonly backed debt that was advocated by an influential independent council of economic advisers in November but that only recently started gaining traction. The proposal would pool all the debt of euro-zone countries that is more than 60 percent of each country’s gross domestic product, considered a marker for a healthy debt level, into a “European Redemption Fund.” Each country would pay off its portion over 20 to 25 years, at rates lower than what struggling countries are paying now, while putting strict limits on future borrowing into their constitutions. Then the fund would be closed.

“Unofficially you quite often hear from government officials that our proposal would be feasible. But it depends on other measures like a fiscal compact and further governance structures,” said Lars Feld, an economist who is one of the five members of the council.

No easy solutions

Merkel and the other leaders of euro-zone countries have tasked Barroso and other top E.U. officials with drawing up plans for shared banking resources that would include regulations, deposit insurance and funds to aid failing banks. Those plans will be presented at an E.U. summit June 28-29.

A smaller, German-government-backed plan to boost growth in the euro zone circulated in Germany on Tuesday, but it consisted of narrower measures such as boosting the lending power of the European Investment Bank and using existing E.U. funds for infrastructure investment, offering little new that would shift the broader course of Europe’s crisis.

For now, Germany’s emphasis is likely to remain on long-term measures that would vastly increase the centralized power of the E.U. in exchange for long-term German guarantees of financial support. If Spain’s problems worsen, Germany may be forced to change its approach.

“There are no straightforward solutions,” said Tanja Boerzel, director of the Center for European Integration at the Free University of Berlin. “I don’t know anyone who has a master plan and says this is going to work.”

Birnbaum reported from Berlin.