PARIS -- Exuberant supporters were still out celebrating Francois Hollande's election as president of France when the first fissures began opening up in the Franco-German motor that drives the rest of Europe.

Although officials on both sides of the Rhine vowed to continue their close political cooperation, German Chancellor Angela Merkel issued a blunt rejection Monday of Mr. Hollande's pledge to renegotiate a Europe-wide fiscal treaty to rein in public debt.

Nor would she countenance deficit spending to boost the economic growth that Europe so desperately needs, pouring cold water on another of Mr. Hollande's campaign promises. Growth could come only through "structural reforms," the conservative Ms. Merkel said.

It was an awkward start for the European Union's newest but most important power couple, the leaders of its two biggest economies and political heavyweights, who together hold the key to how the continent deals with its dire debt crisis. The global economy now depends in major part on what results from the collision between rigid German insistence on fiscal rectitude and the wave of anti-austerity anger sweeping through Europe, with left-leaning Socialist Mr. Hollande riding its crest.

Analysts say an eventual compromise is likely, even inevitable. For all her unyielding words, Ms. Merkel will find it difficult to ignore the burgeoning popular opposition across Europe to Berlin's prescription of deep cuts in public spending. Equally, Mr. Hollande will no doubt discover where the rhetorical luxuries of campaigning end and the tough realities of governing begin.

"Germany, just like France, knows that the two have to get into a close relationship as soon as possible. Given the sovereign debt crisis, the pressure's extremely high for neither side to show any major policy differences," said Daniela Schwarzer of the German Institute for International and Security Affairs. "If Germany and France appear divided, the credibility of promises to rebuild the eurozone is harmed."

The markets, alert for the first signal to beat a retreat, are unlikely to give Mr. Hollande and Ms. Merkel much time to sort out their differences.

For now, the momentum is with Mr. Hollande after his solid defeat Sunday of outgoing President Nicolas Sarkozy, who was such a close ally of Ms. Merkel that pundits dubbed the pair "Merkozy." Mr. Hollande is expected to take office May 15, becoming France's first Socialist president in 17 years.

Besides France, voters in economically sinking Greece threw their weight behind anti-austerity parties Sunday, and popular protests against austerity have also sprung up in financially troubled Spain, Italy and Portugal.

Significantly, calls for a bigger emphasis on reviving economic growth in Europe have also come from the heads of the European Central Bank and the International Monetary Fund. Experts say that even before Sunday's elections, Ms. Merkel had begun to see the writing on the wall.

"This woman is highly pragmatic. I think she feels isolated," said Ulrike Guerot, head of the Berlin office of the European Council on Foreign Relations. "Merkel can feel that there is a pan-European 'enough austerity' argument and doesn't want to go against the wave. She's already starting to go with the wave."

In recent weeks, Ms. Merkel has hinted that she might look favorably on some measures to boost growth. Two weeks ago, she signaled her support for bolstering the European Investment Bank and EU funds for infrastructure projects. EU officials have recommended that the bank increase its lending capacity by an additional $13 billion.

Mr. Hollande, too, has advocated a stronger role for the European Investment Bank. He has also urged creation of joint European bonds to finance infrastructure.

First Published: May 8, 2012, 4:00 a.m.
Updated: May 8, 2012, 4:14 a.m.