Paris — At first glance, with temperatures balmy and thoughts turning toward the traditional August vacation, France seems to be basking in a sunny calm. Yet a closer look reveals a gathering political storm. Next spring's parliamentary elections seem almost certain to provoke a constitutional crisis, and already the nation's politicians are arguing bitterly about how to weather it.
Socialist President Franois Mitterrand said last week he intended to serve his full term until 1988 even if the conservative opposition won the elections and was able to form a government.
This possibility poses a difficult problem because of the unclear nature of the Fifth Republic. A hybrid of the traditional parliamentary system and the United States system of a directly elected president, the Fifth Republic spells out no clear line between parliamentary and presidential powers. Until now, the president's supporters have always controlled the assembly and the president has ruled with few constraints.
But Mr. Mitterrand's Socialists look sure to lose next year, as the President himself seemed to admit in a recent interview by stressing his belief that a Socialist president could govern side by side with a conservative parliament. How he would share power remains unclear.
``The machinery of government will be blocked,'' says Dominique Moisi, director of the French Institute of International Relations. ``It will be domestic civil war.''
To a US observer, the cries of alarm might seem exaggerated. The US often has a president from one party and a Congress dominated by the other.
The policy differences between Mitterrand and the conservative opposition leaders seem minimal. On foreign policy, both are pro-Atlantic alliance and pro-European Community. Even on the more divisive economic issues, Mitter-rand's Socialists have moved toward the center, enacting a tough austerity plan.
The recent history of French government is illuminating. When Charles de Gaulle founded the Fifth Republic in 1958, he vowed to give France strong and stable government in place of the series of weak governments that preceded it. He succeeded. The first quarter century of the Fifth Republic was dominated by four powerful presidents. In 1981 power transferred smoothly to the opposition.
Then Mitterrand and his Socialists lost popularity, and the system began to shake. He had never reconciled himself completely to the Fifth Republic's strict ideological split between right and left.
A return to proportional representation had been in the Socialist platform. It became a necessity to prevent an overwhelming majority for the opposition. So in April, Mitterrand changed the old one-representative-per-district rule and added an element of proportional representation.
His hope is to bring enough small centrist parties into parliament to forge a center-left coalition. If the Socialists won some 30 percent of the vote, preventing the hard-line right from winning an absolute majority, a nonideological figure such as Bordeaux Mayor Jacques Chaban-Delmas could be named prime minister, and analysts such as Mr. Moisi conclude, ``The system might work.''
But if the conservatives win outright, the situation would be much more difficult. Even the Socialists might desert Mitterrand.
Mitterrand says he will continue as president and expresses willingness to live with at least some restraints placed on chief executives. He recently suggested he would retain control of foreign policy while giving the conservatives say over domestic policy.
The conservatives remain wary. Former President Val'ery Giscard d'Estaing and former Prime Minister Jacques Chirac say they would accept such a deal -- if their say over domestic policy is complete enough to dismantle the nationalizations and other controversial measures of the Socialists. The third, and most popular opposition leader, Raymond Barre rejects any power-sharing agreement.
In either case, a political stalemate that could immobilize France might result. At home, the political muscle necessary to carry through the tough austerity measures the Mitterrand government has pursued since its ill-timed reflation of 1981-1982 could vanish. They have brought inflation down and moved the trade account slowly back into balance, but little progress has been made in spurring growth or fighting unemployment.
A weaker government might risk a swelling of imports and a resurgence of inflation to appease the public by putting more dynamism into the economy. Or it simply might not have the strength to continue to administer unpopular austerity.
Similarly, foreign policy could become confused. Mitterrand has directed a vigorous program abroad, moving France closer to the Atlantic alliance, sending troops to Lebanon and Chad, and pushing the European Community toward enlargement and greater integration.
Above all, he proved a strong leader. At this year's Bonn summit, he stood alone against President Reagan's call for a new negotiating round of the General Agreement on Tariffs and Trade. And he decided not to participate in the US space-defense system, launching instead a joint European response to it.
This power to innovate rested on General de Gaulle's legacy of a strong president, transmitted through the Constitution of the Fifth Republic.
But many fear that, after the next parliamentary elections, France will see a much different republic than de Gaulle established.