The fragile, 2 1/2-week-old undeclared cease-fire between Libyan-backed rebels and Chadian government forces is being threatened by President Hissein Habre's tentative preparations to launch a new offensive.
African and Western diplomats are unsure exactly when such an offensive will take place. Nor do they know the strength and duration of the planned military push. But most of them are convinced that President Habre will act ''sometime in the near future,'' as a Western source put it.
The probability of a Chadian government counteroffensive, according to African and Western diplomats in N'Djamena, is anchored in President Habre's fear that the current de facto partition of the country into French and Libyan spheres of influence might become permanent.
The Chadian government's ''nervousness,'' as a Western diplomat described it, was expressed most recently in a lengthy editorial published in the official government newsletter ''Info Chad.'' In this article, written by Pierre Mahamat, the Chadian government condemned officials in the French government ''who are becoming seduced by the belief that the dismemberment of Chad will resolve all problems.''
Indeed, some Chadian government officials express their concern in private that the French might agree to such a partition in order to avoid a direct military confrontation with the Libyans.
French President Francois Mitterrand, in a recent interview in the French daily Le Monde, attempted to allay Habre government fears that a partition of the country would be acceptable to the Socialist government in Paris. President Mitterrand stated point-blank that the partition of Chad was ''unacceptable.'' He called for peaceful negotiations sponsored by the Organization of African Unity (OAU) to ''preserve the territorial integrity of Chad.''
Mitterrand recently sent Maurice Faure, the chairman of the foreign affairs committee in the French National Assembly, to meet with the current OAU chairman , Mengistu Haile Mariam of Ethiopia, in an attempt to pressure the OAU into taking the lead in pursuing a negotiated solution to the conflict.
In addition, the French President has sent his special envoy, Roland Dumas, to Libya and his defense minister, Charles Hernu, to N'Djamena to try to convince both Col. Muammar Qaddafi and President Habre that a military solution to the conflict is impossible and that both sides should work with the OAU to find an acceptable negotiated settlement.
Unfortunately, Mitterrand's recent insistence on negotiations has added to the concern in N'Djamena that the Libyan occupation of northern Chad might become permanent. According to African and Western diplomats in the Chadian capital, President Habre opposes negotiations simply because he believes efforts at a peaceful settlement are bound to be protracted and that the Libyan occupation of northern Chad would gain acceptance meanwhile.
Thus, an African diplomat theorized, ''President Habre has no choice but to pursue the military option. He cannot sit and wait for the Libyans to negotiate their own withdrawal from northern Chad because that just won't happen. Habre must attack to make sure Qaddafi, France, and the OAU realize that the temporary partition of Chad is just that - temporary - and that he is determined to recover the lost territory.''
Most Western and African military analysts in N'Djamena agree that Habre's forces do not have the strength to force the Libyans and their rebel allies from Faya-Largeau and the rest of northern Chad. But a majority assert that the Chadian government now has the military capability to launch a successful guerrilla campaign against the Libyan- and rebel-held positions in northern Chad.
Although Mitterrand has made it clear that French forces in Chad would not participate actively in such an offensive, Western sources in N'Djamena indicate that the French government might lend indirect support to such an attack as long as it did not entangle French combat personnel or fighter aircraft.
In addition, Habre could count on the United States to lend full support to any further Chadian government military efforts since the US government has repeatedly condemned both the Libyan occupation of northern Chad and the possibility of a permanent partition.
Still, even with the open support of the US government and at least grudging French support, few Western and African diplomats in N'Djamena believe Habre will force the Libyans to abandon either Faya-Largeau or the adjacent Aozou Strip.
As an African official here observed, ''It would just be too much for Qaddafi to withdraw from Chad twice in the last three years. He would be humiliated. No, if Habre attacks, Qaddafi's only choice would be to fight back.''