With just two weeks to go before France's legislative elections, President Francois Mitterrand has completed the political groundwork that will help him to retain considerable power and influence even if his Socialist Party is defeated.

For months, political observers here have been preoccupied with the prospect of a constitutional clash between a Socialist president whose seven-year mandate does not expire until 1988 and a National Assembly dominated by his right-wing opponents. Warnings of chaos have alternated with predictions that Mitterrand could find himself reduced to "opening chrysanthemum shows," the derisory French job description for a ceremonial head of state.

Up until now, French Fifth Republic presidents from Gen. Charles de Gaulle to Mitterrand have all succeeded in imposing their will on a pliant National Assembly. An opposition victory in the election, as forecast in the opinion polls, would, therefore, represent the first significant test of the political institutions founded by de Gaulle in 1958.

As the debate over the precise limits of presidential power rages in public, Mitterrand has quietly prepared for a future trial of strength with a politically hostile assembly. Precautionary measures have included the appointment of dozens of trusted aides to key administrative positions, an attempt to reduce the scale of the electoral defeat through the introduction of proportional representation and the laying of political booby traps for a future right-wing government.

French commentators have coined a new political code word, "cohabitation," to denote the uneasy, almost unnatural sharing of power between left and right that they expect to emerge from the March 16 election.

"Mitterrand has taken literally hundreds of measures to pave the way for cohabitation. It's like a schizophrenic. He's been living in 1986 ever since 1983," remarked Serge July, the editor of Liberation, an independent leftist newspaper.

The pace of personnel changes accelerated after July of last year when an official decree reserved 168 key posts in the economy and the state administration for presidential nomination. The decree, which was scarcely noticed at the time, greatly increased the president's patronage powers.

The most significant presidential appointment came last week with the nomination of Justice Minister Robert Badinter as president of France's Constitutional Court. Similar in some respects to the U.S. Supreme Court, the nine-man Constitutional Court will exercise an important role after the elections in adjudicating disputes between the president and the assembly.

Close associates of Mitterrand have been named to important ambassadorial posts such as the United Nations and the Council of Europe, provoking protests from career foreign service officers.

More subtle presidential maneuvers have included a bill putting an end to the French tradition of accumulating several elected offices. Mitterrand has proposed that no official may hold more than two elected jobs. Many political analysts here believe that the real purpose of the law, which is impeccably democratic in appearance, is to force local elections in 1987 as politicians give up "excess" mandates.

Mitterrand's purpose, in the view of most political observers, is to introduce as many electoral checks as possible on the freedom of action of a future right-wing government, particularly in the period leading up to the next presidential election in 1988.

The new electoral system of proportional representation, introduced by Mitterrand last year, will have the effect of boosting Socialist representation in the National Assembly. Recent opinion polls have suggested that the Socialists could win as many as 200 seats in the 577-seat assembly, compared with about 100 under the old system of majority voting in individual electoral districts.

Mitterrand has made it clear that he intends to complete his mandate, even if the opposition wins the election, and will remain an active president.

Neo-Gaullist leader Jacques Chirac this week made it clear that he would insist on being given a free hand by Mitterrand if the opposition wins a clear-cut majority.