PARIS —  French unions and student groups called Monday for a national day of strikes March 28 to protest a youth jobs plan that has already provoked huge street demonstrations and paralyzed many universities.

Labor unions had set a Monday evening deadline for Prime Minister Dominique de Villepin to withdraw the jobs plan or face a possible general strike — but he showed little sign of backing down. Meeting student groups, Villepin calmly urged dialogue.

"There are problems and worries being expressed," Villepin said after the talks, which were boycotted by the largest student group, UNEF. "Let's get together around a table to move forward and find solutions and responses."

The law, passed by parliament this month, is designed to reduce youth unemployment by making it easier for companies to hire and fire. But critics fear it will hurt job security.

Another day of student protests is planned Thursday ahead of the national strike, expected to affect sectors from travel to industry to schools. Individual unions were to offer more details in the coming days.

President Jacques Chirac acknowledged Monday that concerns about the law were legitimate, but said high youth unemployment in France required action. He made a new appeal for talks between opponents and the government.

"The stakes in the next few days are to open a constructive and conscientious dialogue that could improve" the law, he told reporters. Chirac must sign the law for it to take effect next month.

The debate looms large in the run-up to French presidential and legislative elections next year. Polls show the popularity rating of the conservative Villepin taking a beating, and the opposition Socialists have vowed to revoke the measure if they return to power.

Students are angry the law was pushed through quickly.

"They (the government) imposed the jobs plan without consulting anyone," UNEF leader Bruno Julliard told The Associated Press. "They only agree to talks when a million people go into the streets to demonstrate, so we refuse to talk to them until they withdraw it."

Opponents were riding a swell of protest culminating in marches across France on Saturday that drew at least a half-million people. Organizers said 1.5 million took part.

The largest march, in Paris, ended in violence and skirmishes between youths and police at the famed Sorbonne university. Cars, bus shelters and 10 shops were damaged — including a McDonald's restaurant.

A total of 167 people were arrested. Police said Sunday that 52 people were injured — 18 of them demonstrators.

One man injured at the Paris protest was unconscious and in serious condition Monday, police and hospital officials said. The PTT-SUD union claimed the 39-year-old man had been "violently trampled by a police charge."

The unrest continued in pockets Monday. At least 300 students hurled stones and set garbage bins on fire at Louis Armand High School in southern Paris, principal Jean-Armel Le Gall said. No injuries were reported, and the violence ebbed by midday.

Thirteen universities were on strike — with students blockading entrances with classroom chairs and tables — and classes at dozens of others and at many high schools have been disrupted.

The government's new youth jobs contract, passed March 9 by parliament, is designed to lower the 23 percent unemployment rate among the nation's young people. Critics say it would chip away at workers' rights and endanger job security.

The contract is meant to encourage employers to hire, by easing workplace rigidities and allowing them to fire young workers during the first two years of employment without giving a reason.

Business leaders and students suggested Monday the trial period should be shortened, and that companies be obliged to explain their reasoning when they break a contract, but Villepin did not immediately comment on the proposal.