Despite a lull in the fighting and a flurry of diplomatic overtures during the past week, a solution to the latest eruption of Chad's civil war appears more elusive than ever.

As Libyan-backed rebel forces have fortified positions in the north after capturing the strategic oasis of Faya Largeau 10 days ago, France has stepped up its supply of troops and equipment to bolster the 4,000-man army of Chadian President Hissene Habre.

The French contingent of paratroops--said to be only instructors--now exceeds 1,000 and reportedly may grow to as many as 3,000, making the present venture France's biggest military foray into Africa since the 1954-62 Algerian war. The Defense Ministry has refused to divulge the exact scope of the present "Operation Manta."

French troops now form an imposing bulwark, stretching across central Chad from Salal in the west to Abeche in the east, to thwart any assault on the capital of Ndjamena by the rebel forces of ousted president Goukouni Oueddei and his Libyan patron, Col. Muammar Qaddafi.

While the troop reinforcements may have nurtured an uneasy stalemate, French diplomatic efforts to push the antagonists toward the negotiating table have made little visible progress.

President Francois Mitterrand dispatched his chief adviser on African affairs, Guy Penne, to Ndjamena this week to discuss possible peace initiatives with Habre.

At the same time, Roland Dumas, a Paris lawyer and close friend of the president, with good contacts among Arab radicals, flew to Tripoli to try to probe Qaddafi's intentions.

Both emissaries are said to have detected some willingness to explore peaceful solutions, but there seemed to be total disagreement on what to negotiate and who should talk to whom.

Habre says he is prepared to sit down with Qaddafi and draw up a peace agreement provided that the Libyan leader withdraws his soldiers--estimated at 3,500--from Chad.

Qaddafi, however, persists in denying any involvement of Libyan forces and contends that the civil war can be ended only by the two rival warlords, Goukouni and Habre.

But Habre and Goukouni repeatedly have insisted that they will not negotiate with each other despite frequent appeals from other African leaders that they settle their feud.

With an apparent impasse looming on both the military and diplomatic fronts, the French government seems frustrated at being enmeshed in another intractable dispute over Chad--a situation that Mitterrand came to office in 1981 determined to avoid.

France resisted American pleas to intervene early on behalf of Habre for several reasons.

During his years as a rebel leader, Habre infuriated the French people by kidnaping a French woman, Francoise Claustre, and holding her captive for nearly three years.

France cultivated good relations with Goukouni when he was in power and coaxed him into ordering Libyan troops out of Chad two years ago.

When Habre toppled him last year, Goukouni took refuge in Libya, where he began to reorganize his forces with Qaddafi's help.

Besides seeing the civil war in Chad as a local power struggle and not a microcosm of the East-West conflict, France has wanted to preserve chances of improving relations with Libya.

France imports Libyan oil, and Qaddafi has become an important customer for French arms exports at a time when the Mitterrand government is under intense pressure to improve the French trade balance.

But Mitterrand's profound reluctance to perceive Third World struggles in an East-West context lies at the heart of his recent differences with the Reagan administration.

After a long silence, Mitterrand has started to explain his rationale for French policy in the Chadian conflict through selected interviews with French newspapers.

His views were outlined this week in the Paris daily Le Monde.

Mitterrand accused Washington of exerting undue pressure on France to increase its military involvement early to halt the advance of the rebels.

He also complained that France was not informed that the United States dispatched two AWACS radar planes to conduct surveillance over Chad until he read about it in the newspapers.

When the Reagan administration objected to Mitterrand's claims, the French government, to cool the controversy, refrained from further comment.

But French political sources were quoted today as saying that Mitterrand again will challenge the United States in another interview next week with an unidentified French newspaper.

Mitterrand is expected to elaborate further on French aims to halt the fighting in Chad and protect the country's independence. He is also said to be prepared to explain why he did not send French troops into the conflict when Habre's forces were besieged at Faya Largeau.

The French president was backed today in his criticism of U.S. pressure by Michel Jobert, a former minister under both Mitterrand and the late former president Georges Pompidou.

Jobert told the Paris newspaper Le Matin that U.S. appeals for urgent French involvement delayed the government's response and said the Americans exerted their pressure so clumsily and insistently that any government would have been forced to back away.

Jobert also echoed Mitterrand's complaint that the United States wants to use the conflict in Chad to deal a crushing blow to Qaddafi. France to increase its military involvement early to halt the advance of the rebels.

He also complained that France was not informed that the United States dispatched two AWACS radar planes to conduct surveillance over Chad until he read about it in the newspapers.

When the Reagan administration objected to Mitterrand's claims, the French government, to cool the controversy, refrained from further comment.

But French political sources were quoted today as saying that Mitterrand again will challenge the United States in another interview next week with an unidentified French newspaper.

Mitterrand is expected to elaborate further on French aims to halt the fighting in Chad and protect the country's independence. He is also said to be prepared to explain why he did not send French troops into the conflict when Habre's forces were besieged at Faya Largeau.

The French president was backed today in his criticism of U.S. pressure by Michel Jobert, a former minister under both Mitterrand and the late former president Georges Pompidou.

Jobert told the Paris newspaper Le Matin that U.S. appeals for urgent French involvement delayed the government's response and said the Americans exerted their pressure so clumsily and insistently that any government would have been forced to back away.

Jobert also echoed Mitterrand's complaint that the United States wants to use the conflict in Chad to deal a crushing blow to Qaddafi.