Mr. Hollande said Sunday night that in addition to increasing employment and helping the poor, he wanted “to reorient Europe on the path of growth and employment.”

If he should win on May 6, France would emerge as a powerful voice for promoting economic growth in a period of recession in the euro zone and nearly flat growth even in France and Germany. As part of his emphasis on stimulating growth, Mr. Hollande has said he would try to renegotiate a European Union treaty agreed upon in December, under strong German pressure, to limit budget deficits and national debt. He wants the European Central Bank to tolerate more inflation and favors collective euro bonds for national debt, both ideas sharply opposed by Berlin.

But France would very likely have conservative allies in the effort to challenge the German orthodoxy, with which Mr. Sarkozy felt he had to go along.

The new right-wing government of Spain has already tried to defy the European Union on debt limits and to mitigate cuts in public spending in a country where unemployment is about 25 percent and youth unemployment is about 45 percent — more than double the figures in France.

The turmoil in the Netherlands may also land a strong blow against the orthodoxy. The Dutch have been close allies of Chancellor Angela Merkel of Germany in demanding fiscal discipline from euro zone partners, but cutting public spending in the midst of an economic downturn is proving hard even for the conservatives.

Both Mr. Sarkozy and Mr. Hollande promise to go further, to balance the French budget in 2016, Mr. Sarkozy vows, and in 2017, according to Mr. Hollande’s plans. But Mr. Hollande also says he will increase spending first, creating state jobs for teachers and the police and subsidizing job creation in industry. Only later would he raise taxes, he has said.