PARIS — Paris’s subways slowed to a halt and rail lines were disrupted today during a massive strike in France that was expected to give President Unions are protesting President Sarkozy’s plan to trim special retirement packages for some workers, part of his pledges to cut back on costly public services. The strikes began late yesterday and were to last through today.

The first mass-scale problems for travelers and commuters were expected at Thursday morning rush hour. Paris transport authority RATP said traffic would be “virtually nil” on most of its lines. The national rail network said it would be “nearly paralyzed.”

Eurostar trains to London and connections to neighboring European countries were also to be disrupted. With commuters relying on their cars, bottlenecks were expected as early as 5:30 a.m. on major routes into Paris, the national road information service said.

Mr. Sarkozy is facing a number of challenges simultaneously as the economy lags, despite his pledges to invigorate it, and signs of discord arise within his own party over the president’s policies.

The president himself appeared unfazed, saying Tuesday night he would push through the reforms regardless of public protest because “that’s what I was elected for.” Mr. Sarkozy was to be out of the country at an EU summit in Portugal today.

While France’s strikes are famously common, the country has not had any serious ones since Mr. Sarkozy took office. This week’s could be the biggest in years.

Labor leaders hoped the walkout would recall 1995 strikes that paralyzed the country and sapped President Chirac’s appetite for reform. Those strikes — also involving retirement rights — dragged on for three weeks.

Transit workers initiated the strikes, but employees of state-run electricity, gas, and other services also could take part.

Most teachers were not planning to strike, but some schools were expected to close because of transport difficulties.

Air travel also faced potential disturbances, according to civil aviation authorities, who said there was a risk flights would be modified, particularly early in the day if administrative and airport personnel had trouble getting to work.