When Poland's military leader, Gen. Wojciech Jaruzelski, was hustled through the back door of the Elysee presidential palace earlier this week, he can scarcely have imagined the constitutional shock waves he was about to set off in France.

The upsurge of indignation at President Francois Mitterrand's decision to meet the man responsible for crushing the independent Solidarity trade union was predictable. What was not predictable -- and what has created all the fuss here -- was that Mitterrand's own prime minister, Laurent Fabius, would choose to join in the chorus of disapproval by announcing that he was "troubled" by Jaruzelski's visit.

The public disagreement between the president and the prime minister has been front-page news here, swamping the initial debate about the propriety of doing business with dictators. The implications of this unprecedented act of lese majesty have been chewed over by politicians, historians, constitutional lawyers and journalists.

After Mitterrand left Paris Wednesday night for a previously planned trip to the French Antilles, rumors swept the capital that Fabius had tendered his resignation. It required a presidential television appearance from the Caribbean to reassure the nation that a full-scale political crisis was not imminent.

On his return to Paris today, Mitterrand made clear that he had no intention of getting rid of Fabius just four months before important legislative elections. Questioned about the dispute with Fabius, he replied: "Why should I deprive myself of a good government and a good prime minister?"

For many French commentators, this week's controversy has served as a kind of dress rehearsal for the real political drama expected after the elections next March. It is widely assumed that Mitterrand's ruling Socialist Party will lose control of the National Assembly, obliging the president to appoint a right-wing prime minister and government.

That, in turn, is likely to lead to a constitutional clash of a kind never experienced here. The political stability of the Fifth Republic, which was founded by the late Charles de Gaulle in 1958, has depended until now on the president's ability to choose a prime minister and oblige the government to implement his own policies.

Even Fabius' relatively mild expression of prime ministerial independence has shocked a generation of French politicians reared on a doctrine of unadulterated presidential authority. In previous administrations, similar disputes almost always have taken place in private and often have resulted in the resignation of the prime minister.

"When a prime minister finds himself presented with an unacceptable fait accompli, and recognizes it publicly, I think he should resign," commented Jacques Chirac, the head of the neo-Gaullist Rally for the Republic party.

Chirac resigned as prime minister in 1976 following a policy dispute with the president then, Valery Giscard d'Estaing. A right-wing victory next March would make him a leading candidate to become prime minister again under Mitterrand.

A similar stance was taken by Raymond Barre, Chirac's successor as prime minister.

Fabius, who once declared that it was impossible to "slide a cigarette paper" between Mitterrand's ideas and his own, has not explained his unusual public stand on the Jaruzelski visit. Most political analysts assume that he wanted to consolidate an image of caring deeply about human rights. He has made little secret of his own presidential ambitions.

After a meteoric rise, largely thanks to Mitterrand's patronage, Fabius, 39, has suffered setbacks in recent months. Fellow Socialists have questioned his political sincerity. There was widespread resentment among party members about the way he pinned the blame for the sinking of a Greenpeaceship by the French secret services on former defense minister Charles Hernu.

Fabius' standing in opinion polls, exceptionally high after he took office in July last year, slumped after a televised debate with Chirac in October when he came across as aggressive and impolite.

Why Mitterrand risked a major public outcry by receiving the Polish president is more mysterious. Having first agreed to meet Jaruzelski, he then did his best to snub him. The junior minister assigned to greet the Polish leader at the airport developed a sudden "cold" and a low-level protocol official stood in for him. Then the Polish motorcade was waved away from the front of the Elysee.

One possible explanation is that Mitterrand was testing the limits of presidential powers. By ignoring the advice of his prime minister, according to this argument, he was demonstrating that the president is ultimately responsible for the conduct of foreign policy.

In a television interview yesterday, Communist leader Georges Marchais voiced the suspicion that Fabius had cleared his act of defiance with Mitterrand beforehand.

"They are preparing the ground for the period after the elections , trying to demonstrate that it is possible in practice to have a president with one position and a prime minister with another," he said.

The problem with this "conspiracy" scenario is that both Mitterrand and Fabius may have done themselves more damage than good as a result of the Jaruzelski visit. The controversy has convinced many right-wing politicians that, if Mitterrand has major disagreements with a Socialist prime minister, it will be impossible for him to "cohabit" (French political jargon for "reaching a working agreement") with the right.