While reinforcing its military position in Chad, France is stepping up pursuit of a diplomatic solution to the conflict. But officials here say no solution, military or diplomatic, is in sight, with a de facto partitioning of the country a possible result of the standoff.
Militarily, the French strategy is to put enough French troops and materiel on the ground to deter the Libyan forces from moving southward. From an original announcement that several hundred paratroopers were being sent to ''train'' Chadian soldiers, the force has grown into France's biggest show of force since the Algerian war.
The Defense Ministry said Sunday that France had completed its airlift of paratroopers to Chad. While ministry spokesmen refused to specify the number of troops involved, reports here say there are now between 2,000 and 3,000 French paratroopers in Chad. In addition, four French Jaguars and several Zairian fighter planes arrived Sunday at N'Djamena's airfield to provide air cover for the French troops. Underscoring the importance of the reinforcement, one of France's most experienced officers, Brig. Gen. Jean Poli - a veteran of African operations - was named Friday to take command of the force.
The French troops are deployed in a defensive line across the country some 200 miles north of N'Djamena. This leaves Chad effectively cut in half: the north being occupied by an estimated 3,000 Libyan troops and an equal number of rebels under Goukhouni Woddei, the south by the French, about 2,000 Zairian trrops, and about 4,000 government troops loyal to President Hissein Habre.
Zairian President Mobutu Sese Seko made a surprise visit to the Chadian capital Saturday to publicly reinforce his country's support for Habre's struggle against Libya.
General Poli is under strict orders not to advance against the Libyans, but if the Libyans move southward and confront his forces, he will fight - and officials here are confident that his crack troops equipped with sophisticated antiaircraft missiles would give the Libyans a quick drubbing.
The French strategy, then, is simply to block Libya's military option, forcing Col. Muammar Qaddafi to the negotiating table. The plan seems to be working to a certain extent: For a week now, Chad's desert battlefields have been calm.
The pause has been filled with quiet diplomacy. In an interview with French television last week, Mr. Qaddafi confirmed he had received Mr. Mitterrand's personal attorney, Roland Dumas, in Tripoli to discuss the Chad problem. Mr. Dumas reportedly will fly to Tripoli again this week.
''Libya wants to find a pacific solution to the Chad problem and is willing to do everything to find such a solution,'' Mr. Qaddafi said in his television interview.
But the French continue to insist that Mr. Qaddafi pull his troops out of Chad, while Mr. Qaddafi insisted in his interview that no Libyan planes or troops are directly involved in the conflict. ''One cannot envisage in the short term a solution to the Chadian question,'' the Libyan leader concluded. French officials use the same line.
But French and Chadian officials hope that with the balance of power reestablished in the country, negotiations will result between sworn enemies Woddei and Habre.
So far, Mr. Woddei has said that he will only negotiate with N'Djamena if Mr. Habre steps down. For his part, Mr. Habre refuses to talk to Mr. Woddei, insisting that his only viable negotiator is Mr. Qaddafi.
But at least one informed and independent Chadian, Jean Bawoyeu Alingue, Chad's former ambassador to Paris and Washington, believes that Mr. Habre and Mr. Woddei will soon be pushed into negotiations.
''Neither Mr. Habre nor Mr. Woddei is the master of this game,'' Mr. Alingue said in an interview with The Christian Science Monitor. ''France and Libya are, and if both of them want negotiations, there will be negotiations.
''France obviously wants negotiations,'' he continued. Pressure from Paris on Mr. Habre is probably already being exercised, he added, since Mr. Mitterrand's advisor on African affairs, Guy Penne, was sent to N'Djamena last week to talk to the Chadian leader.
The obvious question mark, then, is whether Colonel Qaddafi will push Mr. Woddei to the negotiating table. Mr. Alingue believes that with French troops blocking his advance, the Libyan leader will find occupation in the north too costly, both financially and diplomatically.
''Already, his friends in the Organization for African Unity are criticizing him,'' Mr. Alingue said, referring to the declaration by nine African chiefs of state in Brazzaville last week that called for an end of the ''interferences'' by ''neighboring countries in Chad.'' Ethiopia's leader, Lt. Col. Mengistu Haile Mariam, a friend of Colonel Qaddafi and the president of the OAU, was asked to mediate the conflict.
This leaves Mr. Alingue hoping that a face-saving way can be found to have Mr. Qaddafi withdraw - say, by giving him certain rights in the northern Aozou Strip that Libya has long claimed.
The stalemate leaves the French in a difficult position, under pressure from both Washington, Francophone Africa, and Mr. Habre. All these forces seem to want Paris to whip Mr. Qaddafi militarily, forcing him out of the country rather trying to talk him out.
According to French officials, pressure on Francois Mitterrand has been insistent. Mr. Habre has scolded the French President publicly for succumbing to the pressure of a ''pro-Libyan lobby;'' in telephone calls to the Elysee Palace, African leaders such as Felix Houphouet Boigny of the Ivory Coast and Col. Seyni Kountche of Niger have been more discreet but equally insistent with France about Qaddafi.
But the most annoying pressure in French eyes came from Washington. French officials say that President Reagan has sent several ''Dear Francois'' letters ticking off the actions Washington desired of the French in Chad. In an interview with Le Monde last week, Mr. Mitterrand said the conflict in Chad would have been less complicated if Washington ''had not weighed so heavily in the balance.''
Beyond the quarrel over the letters, deep-seated disagreements persist between Paris and Washington over the nature of the Chad crisis. The French see the Reagan administration as obsessed with Colonel Qaddafi and unaware of complex problems Chad would face even if Libyan troops were not involved. In his interview, Mitterrand made it clear he would not take part in American ''preoccupations with the ambitions of Colonel Qaddafi'' and try to ''overthrow his regime, toward which (France) harbors neither hostility nor ill will.''
The French are also uncomfortable with Mr. Habre. Officials refer to him as ''a troublemaker'' who is largely responsible for plunging Chad into an almost unending civil war in the mid-1970s.