BRUSSELS — In the face of pressure from the embattled euro zone countries Italy and Spain, European leaders agreed early Friday to use the Continent’s bailout funds to recapitalize struggling banks directly, cheering financial markets but prompting unease in Germany, whose taxpayers may face more risk.

Stocks and the euro opened strongly higher in Europe and were still rising through mid-afternoon — a clear suggestion that the summit, by breaking new ground, had exceeded expectations. Analysts cautioned that earlier summit agreements had prompted market rallies that proved short-lived.
The decision, by leaders of the 17-nation euro zone, would allow help to banks without adding directly to the sovereign debt of countries, which has been a problem for Spain and potentially for Italy. Both countries have seen the interest rates on their debt rise to levels that would be unsustainable in the long term, and the Italian and Spanish prime ministers, Mario Monti and Mariano Rajoy, came here to push their colleagues to help.
Though the German chancellor, Angela Merkel, made concessions, they came with conditions, and some of the detail remained unclear Friday, prompting calls for more clarity to be provided quickly.
The deal was struck after the Italian and Spanish leaders said they would block all other agreements — on a 130 billion euro or $163 billlion growth pact, for example — until their colleagues did something to help take the pressure off the third- and fourth-largest economies in the euro zone.
If their countries could not go to the markets to roll over their debt, Mr. Monti and Mr. Rajoy argued, there would be an existential threat to the euro in the short to medium term.
Spain is seeking 100 billion euros to recapitalize its banks, damaged by a property bubble.
Mr. Van Rompuy called the agreement a “breakthrough that banks can be recapitalized directly,” which represents a concession by northern European countries, including Germany.
As a condition, though, the leaders agreed that the euro zone’s permanent bailout fund, the 500 billion euro European Stability Mechanism, due to come into being next month, could act only after a banking supervisory body overseen by the European Central Bank had been set up. That should happen by the end of the year, Mr. Van Rompuy said.
François Hollande, the French president, said Friday that the agreement offered a number ways to give troubled economies the rapid assistance that they had been seeking.
“It’s very important that we put into motion procedures for immediate action — that was something much hoped for,” he said. “Bank supervision for a recapitalization of the banks will take a bit more time, but this is a move in the right direction.”
“To have defined a vision for the economic and monetary union” was a fundamental step toward answering the question “what we do we want to do together,” Mr. Hollande said.
Graham Neilson, chief investment strategist at Cairn Capital, an asset management and investment company in London, noted that while the agreement represented progress, some fundamental issues were not addressed.
“The burden of future risk is being shared more widely, meaning the chances of a euro zone breakup have been lowered for the short term,” he said. “But at the same time, the longer-term ante is higher for all involved and the root causes of the structural imbalances remain.”
Ms. Merkel has argued that risks could only be pooled among euro nations if decision-making on key issues were also shared. She insisted that the decisions in Brussels were based on Germany’s basic philosophy of how to solve the crisis, through a series of checks and balances, with rewards for meeting conditions that are governed by a strict set of controls.
Unease emerged in Berlin, however, over the extent to which the principles of the euro zone bailout fund, the E.S.M., had been altered from the original agreement that is to be put to vote in Parliament later Friday.
Members of the budgetary committee of the German Parliament called an emergency meeting to debate the impact the changes could have on the vote, which was expected nevertheless to pass easily by a two-thirds majority.
Yet criticism from members of the opposition Social Democrats, and within the chancellor’s own party, who charged that allowing banks to tap directly into the E.S.M. brought the country one step closer to a common sharing of debt, revealed the extent to which the chancellor is torn between pressure from abroad to support swift and decisive measures to appease markets, and resistance within Germany to taking on too great of a role in bailing out the weaker members of the Continent.
“It is not so easy for Ms. Merkel,” said Tanja Börzel, a political scientist from Berlin’s Free University. “She can’t simply charge ahead, but has to consider her domestic audience and the democratic and legal procedures we have in Germany."
The deal reached in Brussels was particularly important for Mr Rajoy, who had resisted German pressure over the past two weeks to accept tougher bailout terms and can now return to Madrid with an agreement in hand that eases concerns over Spain’s creditworthiness by ensuring that the rescue will not add to the country’s sovereign debt, as the funding will flow direct to the banks.
Spain also ensured that, when its banks are bailed out by the euro zone rescue fund, the fund will not be treated as a preferred creditor. This prospect had deterred some private investors since, in the event of a default, they would have faced proportionately bigger losses.
José Maríá Méndez, director general of the association of Spanish savings banks, or cajas, described the European deal as “very positive” for Spain.
“It now seems to me a fair agreement between European partners that sets the foundation for a banking union,” he said at a conference on the euro debt crisis in the northern Spanish city of Santander.
The deal, however, is less favorable for Italy than for Spain, according to Nicholas Spiro, managing director of Spiro Sovereign Strategy, a London consulting firm that assesses sovereign debt.
“Mr. Monti only managed to extract a commitment that the rescue funds will, if called upon by Rome, purchase limited amounts of government debt provided Italy sticks to its current reform program,” Mr Spiro wrote in a note to investors. “What’s more, any bailout loans to Italy would still be given seniority status.”
Mr. Monti, an experienced European player and former European Union commissioner, hailed the agreement as a “very important deal for the future of the E.U. and the euro zone,” adding, “it is a double satisfaction for Italy.” He had argued that other euro zone leaders must find ways to help “virtuous countries” like his own and Spain, he said, which were fixing their economies and were solvent, but were under speculative market pressure.
Countries that request bond support from the rescue fund will have to sign a memorandum of understanding setting out their existing policy commitments and agreeing to a timetable. But they will not face the intrusive oversight of a “troika” of international leaders to which Greece, Ireland and Portugal have been subjected, Mr. Monti said.
The euro zone “will be strengthened by this,” Mr. Monti said. Italy has no immediate plans to ask for help from the existing funds, he added, on the assumption that bond yields would ease after this agreement.
The summit outcome was welcomed by the Institute for International Finance, a bank lobby group, though its market monitoring group issued a statement calling for more detail.
“The signal of intention to establish a single supervisory mechanism creating the possibility of recapitalizing banks directly is encouraging,” it said. “Likewise, the indication that EFSF/ESM funds for Spain’s banking sector would not have seniority over private claims reflects an important recognition that such seniority would undermine the objective — breaking the negative feedback loop and restoring confidence in euro area sovereign debt markets.”
“Nevertheless, such statements require concrete and immediate steps to give confidence to all parties that these directions will be fully realized,” the statement added.
James Kanter in Brussels, Melissa Eddy in Berlin, David Jolly in Paris, Raphael Minder in Madrid and Stephen Castle in London contributed reporting.