PARIS — Striking transport workers cut train service and forced Parisians to walk, bike, or skate to work today in a pivotal standoff with President Sarkozy over his bid to pare down labor protections.

Workers for the national rail network and Paris public transport authority voted to extend their strike into tomorrow. They are threatening an open-ended strike, with daily votes on whether to continue, as they try to hang on to special retirement benefits that Mr. Sarkozy wants trimmed.

Mr. Sarkozy, however, set the stage for negotiations with unions and companies over the retirement issues that prompted the strikes. “It’s advancing,” Prime Minister Francois Fillon said.

Employees of the national rail and subway authorities and the gas and electric companies walked off the job to protest plans to extend the retirement age for some 500,000 public sector workers and change other special benefits certain sectors have enjoyed for more than a half-century.

Unlike the scattered strikes that have long dogged France — including an October 18 transport strike seen as a warning volley against Mr. Sarkozy’s reforms — this labor action and other strikes planned in the coming weeks could be a decisive test of Mr. Sarkozy’s campaign promise to overhaul France to make it more competitive.

The popularity of the strikes also is a question.

“I support the idea of strikes, but not this strike,” a man who skated five miles to his advertising job, Xavier Michel, 25, said. This strike, he said, hurts “the little guys like us” who are “basically taken hostage.”

The strikes started last night when the SNCF rail authority halted service on most lines. Only 90 of 700 trains were running. The Eurostar between Paris and London was running as usual.

Paris transit workers joined in today. Gas and electricity workers went on strike, too, threatening targeted blackouts to illustrate their grievances over the retirement reform.

Students protesting a university reform added a volatile note to the transport strike, blocking at least 35 of France’s 85 universities.

Students opposed to the blockages were doubly punished — without transport and unable to get into class. “Not only did it take me an hour and a half to get here, I can’t get in,” law student Michael David said.

Paper signs reading “No Service” dangled at subway stations and bus and tram stops in the capital. The highway circling the city was jammed with vehicle traffic as many commuters drove to work. Others walked or used the city’s popular new rent-a-bike system.

Opinion polls suggest Mr. Sarkozy has the public on his side as most agree with his arguments that retirement rules are outdated, unfair, and too costly.

Mr. Sarkozy wants everyone — including the rail and utility workers, sewer workers, state bank employees, and workers at the Paris Opera and the Comedie Francaise theater company — to retire after 40 years of service instead of the 37.5 years they currently work.

Despite tough talk, the head of the Communist-backed CGT union, Bernard Thibault, proposed a potential opening, suggesting talks with various companies and relaxing earlier demands that it would only negotiate with the government directly, according to Le Monde.

Mr. Sarkozy’s top aide, Claude Gueant, told Le Monde that the union leader had moved so that “the crisis can be eased on the first day of conflict.”

The conservative Mr. Sarkozy is being pressured from all sides as his government moves ahead with cost-cutting reforms, from trimming bureaucracy to shuttering courthouses and allowing universities to charge tuition and attract private funding.

The head of the main employers’ association, Medef, called the strike embarrassing to France’s global image. Laurence Parisot urged the French to “abandon this taste, which I think is a bit masochist, for conflict, for struggle.”