PARIS, March 21 — Facing crippling strikes and growing civil unrest, Prime Minister Dominique de Villepin of France on Tuesday discussed watering down his contentious new labor law with legislators.

Students threw a burning mattress at police officers Tuesday in Paris as they protested the youth labor law.
But union leaders, who have refused to begin a dialogue with the government until it has rescinded the law, showed no signs of budging on their promise to carry out nationwide protests and strikes next week. The law gives companies the right to hire employees 25 or younger for a two-year trial period, during which they can be fired without cause.

"The basic demand of the youth and of employees is that the law be withdrawn," said Gérard Aschieri, head of the Unitary Union Federation, France"s largest teachers union syndicate. "He has to respond to the people in the street."

While Mr. de Villepin has repeated his refusal to withdraw the law, legislators from his governing Union for a Popular Movement party said there was a growing consensus that it must be amended to make it more palatable to opponents. The prime minister himself suggested possible changes at meetings on Tuesday with legislators from his party.

"The prime minister was very closed last week, but was more open to the idea of amending the law today," said Éric Woerth, a party legislator who attended the meeting. "Almost everyone agrees that we must do something, not because of the mobilization of the unions, but because the battle of explaining the law has been lost with the young."

Any significant weakening of the law will represent a serious blow to the prime minister, who hopes to run for president next year. It will also signal another defeat in France"s long struggle to break the stranglehold of its rigid social-welfare system, which economists say has kept growth sluggish and unemployment high for decades. While there is no guarantee that the new law will create jobs, as the government contends, bowing to student and union pressure on it will call into question the current administration"s ability to restructure the system.

France has a strong tradition of often violent demonstrations and paralyzing strikes that is largely tolerated by the broader population, which has a cultural mistrust of government even as it retains a deep sense of dependency on the state. The resulting tendency to rebel against any attempt to curtail entitlements has cowed many administrations into backing down from bold policies that might have helped remake the system in the past.

But as one commentator wryly noted, the administrations often pay by losing subsequent elections anyway. Even Mr. Woerth seemed to sense the quandary. "It won"t be a glorious exit," he said.

Many people in France are already predicting Mr. de Villepin"s political demise as a result of the crisis. He has come under intense criticism from opponents and from within his own party for pushing the law forward without first campaigning for it among the unions and students most affected by it. His chief rival, Interior Minister Nicolas Sarkozy, by contrast, ushered in an immigration law last year by lobbying potential critics before submitting it to Parliament.

Angered at not being consulted this time and sensing the government"s weakness, the students and unions are now taking a hard line.

Tens of thousands of students marched in major French cities on Tuesday, with some violence breaking out in Paris, where a group of youths smashed the windows and rear-view mirrors of cars along a street behind the Sorbonne. Hotel workers on the street, Rue Gay-Lussac, said fights had broken out between groups of students.

Meanwhile, a witness told Agence France-Presse that the national riot police beat a man unconscious during a melee at Place de la Nation on Saturday night. The victim, a 39-year-old postal worker and union member, Cyril Ferez, briefly regained consciousness but lapsed into a coma, the news agency reported. He remained in a coma on Tuesday.

The possibility of the serious injury or death of a protester at the hands of France"s notoriously tough riot police is what the government fears most. Such incidents have fueled protest movements and helped end political careers.

Hoping to defuse the situation, Mr. de Villepin has opened the possibility of amending the new law. He had hoped the law would lead to more hiring, helping to trim the 22 percent unemployment rate in the age group affected by it.

Now, he is discussing shortening the trial period to one year and requiring companies to explain to dismissed employees exactly why they were let go, though without giving them legal recourse.

But is not clear that even those changes will satisfy opponents.

"Even one year is still excessive," said Mr. Aschieri, the union leader. "In most employment contracts, trial periods are from one to six months."

In any case, even legislators like Mr. Woerth say the changes would effectively gut the law, making the "first employment contract" it defines little different from other short-term employment contracts already in effect and removing any incentive for employers.

"The problem is that it will kill the C.P.E.," said Mr. Woerth, using the French abbreviation for the first employment contract. "The more we modify the law, the less attractive it is for companies."

Ariane Bernard and Maia de la Baume contributed reporting for this article.