Civil servants across the country staged a one-day strike for better pay Thursday, disrupting public services and presenting Premier Michel Rocard with the toughest challenge of his five months in office. There was no way to determine how many of the estimated 5 million civil servants participated. In Paris, subway and bus service was cut by one-half to two-thirds. Many commuters feared the worst and drove into the city, resulting in huge traffic jams. Some highways leading into Paris were backed up as much as 17 miles. Air France canceled 31 flights and major rail lines were running at one-half to two-thirds their usual number. Mail went undelivered and teachers didn't show up for classes in many parts of the country, and many public offices were closed. ``The worst thing that could happen would be that the government continue in its obstinacy,'' said Jean Kaspar, national secretary of the Socialist-run French Democratic Confederation of Labor, at a demonstration in central Paris. Andre Bergeron, head of the Worker Force union, said the government must ``concede something and come to an agreement next week or risk finding itself in an inextricable situation,'' perhaps involving more and longer strikes. Public service employees received a 1 percent raise in March and 1 percent in September. They have been offered a 2.2 percent increase for 1989. Inflation is expected to hit 2.8 percent in 1988, and the public workers see themselves losing 0.8 percent in purchasing power. Maintaining purchasing power is not the only demand of the seven different unions representing public workers, but it is far and away the most important one. Rocard has been criticized by the conservative opposition and by his own Socialist Party. Civil service workers in France traditionally vote left, and they are especially disappointed by the lack of sympathy they perceive on the part of the Socialists, who took over from the conservatives after spring elections. The government received a shock in August when the monthly trade deficit nearly tripled to $1.5 billion. With little prospect of the trade deficit improving much, officials are afraid any relaxation in austerity measures will increase inflation and lead to an even wider trade deficit. Alain Juppe, secretary-general of the conservative Rally for the Republic party, accused Rocard of failing to start consultations with labor soon enough. He criticized the premier for trying to deal with different types of employees on a case-by-case basis instead of working out an overall solution. Pierre Mauroy, a former premier who is now head of the Socialist Party, publicly castigated Rocard for his approach. In a radio interview Wednesday, Mauroy expressed his ``solidarity with the strikers'' and said, ``This situation cannot continue. They cannot be the only ones to see their purchasing power diminish.'' The workers believe that the French economy has been improving lately and that after years of austerity, they should now benefit. The government has pleaded for more time, six months to a year. Police and firefighters are public sector employees but they don't have the right to strike and did not participated in Thursday's action. Nurses in public hospitals can strike but are required to provide minimum service. Air traffic controllers also are public employees but, like nurses, are required to provide minimum service.