Mr. Sarkozy has said that he will stand firm in plans to cut 22,900 civil-service jobs this year, including more than 11,000 in education, and 35,000 next year. The government says it intends to accomplish the reductions by replacing only half of those who retire.

But the unions see a direct threat, and students are worried about fewer teachers and fewer opportunities for good jobs. With Mr. Sarkozy at historic lows in opinion polls, union leaders clearly feel they have a chance to force him to retreat. But the same polls also show that the French generally support Mr. Sarkozy’s reforms, if not the president himself.

As much as 55 percent of the state budget currently goes to pay for civil servants and state pensions. Mr. Sarkozy and his prime minister, François Fillon, say they intend to have a balanced budget by 2012. Mr. Fillon was encouraged on Thursday by reports that economic growth was up in the first quarter, and that the French economy was likely to grow 1.7 percent to 2 percent this year.

Thursday evening, Mr. Sarkozy told journalists that French citizens had “the right to strike,” but also “the right to work.” He defended his reforms and said, “Every time we change something in our country, actions undertaken to better answer the expectations of the French for their schools raise worries, even dissatisfaction, and these worries sometimes, like today, express themselves through strikes.”

Mr. Sarkozy also said the government would draft legislation to ensure that schoolchildren were watched over by municipal employees in future strikes, so their parents could go to work, although the unions say that the plan undermines the right to strike. The legislation would require a 48-hour warning of a coming strike.