Pressure mounts on Chirac over rail strike, Chad. At stake is outcome of next French presidential election

It began with a small click. A second later, the computer flashed off, the lights went out, and the electric heater stopped running. Welcome to France's growing crisis. What started more than three weeks ago as a wildcat rail strike has widened into the largest labor disruption since 1968, producing blackouts at home and fallout around the globe. Repercussions are being felt in the world currency market and perhaps even in far-off Chad, a conflict that confronts France's weakened premier with an uncomfortable new challenge.

Both the United States and France's African allies have been pushing for a strong French response to Libyan aggression in the former French colony.

Preoccupied with his problems at home, Prime Minister Jacques Chirac wants to avoid a full-scale conflict with Libya. He hesitated for three days before ordering French Air Force jets to retaliate Wednesday for the initial Libyan raid in southern, French-defended Chad. He described the Libyan attack as an ``insect bite'' and insisted that he had no intention of engaging France in ``an adventure'' in Chad.

After renewed Libyan attacks yesterday, pressure is mounting to step up the fighting. French officials said they would continue to respond to Libyan attacks on southern Chad with ``firm ripostes.'' At risk, observers say, is French credibility. Chadian President Hissein Habr'e, backed by the rest of Francophone Africa, wants France to help push the Libyans out of northern Chad.

So does the Reagan administration, which has actively supported the French military effort by sending $15 million in military aid to the Chadian government. French officials fear that unless France acts forcefully against Libya, the US will step in and displace France as the dominant power in western Africa.

Back in Europe, France also faces increasing tensions with neighboring West Germany. In this case, the cause of tension is monetary.

During the last week, tumultuous foreign-exchange trading has pushed the French franc below its legally permitted value against the German mark within the European Monetary System.

The problem, economists say, is a mix of German economic strength, which is fueling a rise in value of the mark, and French economic weakness caused by its labor chaos, which is forcing down the franc.

To deal with these tensions, observers agree, France needs labor peace. But the strikes are mounting. Although some train conductors have trickled back to work this week, permitting the restoration of minimum service, the new walkout of urban transport, postal,and, perhaps worst of all, electrical workers has increased the average Frenchman's inconvenience.

Workers are demanding pay increases above the 2 percent inflation rate in order to make up for lost purchasing power. Mr. Chirac refuses to accommodate them. If the nearly 5 million public-sector workers win concessions, the prime minister argues, then all other workers would start demanding them.

The spread of such demands, he explained, would relaunch inflation, worsen France's trade deficit by making its products uncompetitive, and lead to ``500,000 to 600,000 more unemployed workers within the next 15 to 18 months.''

The struggle has uncovered buried social problems. Workers who swallowed five years of Socialist-led austerity now feel that they are being asked to make sacrifices while the conservative government subsidizes farmers and gives gifts to the rich through measures such as abolishing the wealth tax.

At stake is the outcome of France's presidential election scheduled for next year. If Chirac faces down the strikers, political analysts say, he would cement his leadership of the country's conservative forces. He would become the front-runner to challenge Socialist President Fran,cois Mitterrand.

But if the strikers win large wage increases, the defeat could destroy the prime minister. Chirac's reputation as a man who talks tough, only to crumble in a crisis, would pass the initiative to one of his conservative challengers, such as former President Val'ery Giscard d'Estaing or former Prime Minister Raymond Barre. Mr. Mitterrand also would emerge strengthened.

Meanwhile, serious business disruptions are emerging. Company officials report high absenteeism. And when people do come to work, they often arrive late and leave early.

Typical was the Cr'edit Lyonnais bank near the St. Lazare station, which opened an hour late and closed an hour early yesterday to let employees get a head start home. And no deposits were taken when the electricity went off, shutting off teller terminals.

Industry and trade officials say it's too early to tell how much the strikes are costing French businesses. But the conservative daily Le Figaro yesterday estimated the loss at 6 billion French francs - almost $1 billion.

With subway service spotty, Parisians have stopped going out at night.

``People can't get here, and even if they could, they're afraid there would be blackouts,'' said a ticket saleswoman at the trendy St. Germain cinema.

Of course, not everyone is miserable. Officials at Air Inter, the domestic airline carrier, say they've flown 100,000 more people since the strike began. Hardware stores are doing a brisk business selling battery-powered lamps.

Improvisation has become the watchword. At the International Design School in the Marais district, lights went off in the middle of class. Students lit candles and continued working.