PARIS — President Sarkozy’s conservative party won a clear parliamentary majority yesterday in elections seen as crucial to his vision for opening up France’s economy, although the left did far better than expected by capitalizing on fears of giving Mr. Sarkozy too much power.

Mr. Sarkozy’s UMP Party will face little resistance to the rash of measures he plans to introduce within weeks to make France’s sluggish economy more competitive and less protective.

But yesterday’s legislative runoff suggests that voters in France, long driven by leftist ideals, wanted to send the hard-driving and American-friendly president a message that his powers are not absolute, and to keep their concerns in mind.

Some have even predicted mass street protests — like those that stymied President Chirac’s efforts to free up the economy — or an eruption of violence in France’s housing projects if Mr. Sarkozy goes too far, too fast.

“The French showed they did not want to give all of the power to Nicolas Sarkozy,” a former justice minister, Elisabeth Guigou of the Socialist Party, said last night.

With all but 36 seats left to call, Mr. Sarkozy’s party and its allies had at least 330 National Assembly seats, and the left had 206, according to the Interior Ministry. In percentage terms, the popular vote was even closer: the Socialist Party and their allies got about 49%, just behind the parties on the right. Turnout was around 60%, near a record low.

Pollsters projected that when the counting was finished, right-leaning parties would get 339–345 seats, while the opposition left led by the Socialist Party would have 228–234 seats.

That means the UMP will be weaker than it was in the outgoing Parliament, where it enjoyed 359 seats to the Socialist Party’s 149.

It marked the first political stumble for the 52-year-old Mr. Sarkozy, the son of a Hungarian immigrant, since he was elected president last month. Socialist Party leader Francois Hollande said his party had resurrected itself. “It’s good for the country,” he said. “France will walk on both legs.”

Last week’s first round of voting had left the Socialist Party expecting just more than 100 seats, while the buoyant UMP was looking forward to the strongest parliamentary majority in the history of modern France.

Then, in just seven days, the Socialist Party tapped into fears of a rubber-stamp parliament for Mr. Sarkozy and worries about a 5% sales tax increase, intended to finance social programs.

Leftists said the tax would hurt poor and middle-class consumers, and Mr. Sarkozy felt obliged to release a public statement saying he would not allow the tax increase if it hurt purchasing power.

“The government started to govern too early,” Etienne Schweisguth of the Institute of Political Sciences said.

Despite the UMP’s weaker than predicted performance, the result still marked a milestone: It was the first time since 1978 that voters returned an outgoing parliamentary majority to power.

“France needs a kick in the derriere,” said businessman Emmanuel Dochie de la Quintane, 35, on his way to vote for a Mr. Sarkozy candidate in Paris.

Prime Minister Fillon said the right would waste no time in using its majority to “resolutely modernize” France, approving reforms on labor, employment, consumer spending, law and order, universities, immigration, and reducing the disruptiveness of strikes.