N'Djamena is beginning to feel like the capital of a nation at war. The usually quiet, serene atmosphere of this small town on the banks of the Chari River is punctuated by the constant rumbling of American C-141 transport aircraft bringing in US military supplies, French DC-8 and other aircraft unloading French military equipment and soldiers, and Chadian DC-3s and DC-4s ferrying military equipment and soldiers between N'Djamena and the strategic eastern town of Abeche.
In the streets of N'Djamena, djellaba-clad Chadian men and women wrapped in colorful African clothing walk side by side with some 500 khaki-green uniformed French troops and 2,000 crack Zairian paratroopers.
N'Djamena's mood is clearly becoming more tense. The Chadian government has canceled its daily press conferences, banned similar briefings by the French Embassy, forbidden foreign journalists from traveling to other parts of Chad, and placed strict censorship on all outgoing material.
The growing tension was further reflected in a government statement issued after an emergency Cabinet meeting over the weekend.
The statement, read by Chadian Information Minister Soumalia Mahamat, called for the mobilization of Chad's entire 5 million population against Libyan invaders. And the statement again requested the ''direct, massive, and immediate intervention of the military forces of France and the United States.''
The event that triggered the emergency Cabinet meeting and the statement was the loss of Faya-Largeau last week to the Libyan-backed forces of rebel leader Goukhouni Woddei. The battle for Faya-Largeau and the fall of that northern oasis town Aug. 10 to the rebels was described by a senior Western diplomat in N'Djamena as ''the most blatant intervention so far by the Libyans in Chad.''
In that battle, President Hissein Habre's troops were forced to abandon Faya-Largeau in the face of a massive Libyan-directed ground and air assault, which reportedly included MIG fighter aircraft, tactical bombers, tanks, heavy artillery, and an estimated 3,000 to 4,000 Libyan-recruited ''Islamic legionnaires,'' in addition to Woddei's rebel forces.
What is perhaps as significant as the strength of the Libyan military assault on Faya-Largeau is that Libya now is reportedly striking positions far south of Faya-Largeau, including the strategic towns of Oum Chalouba and Kalait, which government forces reportedly have vacated, as well as Koro Toro.
According to a senior Western diplomat, the significance of these attacks is ''that they prove that Libyan leader Muammar Qaddafi is not just content with taking Faya-Largeau, as many people at first believed, but that he is prepared to press south - possibly all the way to N'Djamena. Western intelligence also reports that Libya is continuing to build massive military stockpiles at Faya-Largeau.
It is still too early to tell exactly what the Libyan leader has in mind for Chad. But most Western military analysts here say they think Colonel Qaddafi will continue his military campaign under the guise of supporting the ''legitimate Chadian government in exile'' - that of rebel leader and former Chadian President Woddei - until Habre elicits a clear military counterresponse from Habre's key foreign supporters, especially the French.
Judging from recent events in Chad and in Paris, the Libyan leader appears to be doing just that.
Although the French government continues to insist it is acting within the 1976 French-Chadian military cooperation agreement, which prohibits the use of French military personnel or aircraft in combat roles, the recent arrival of French troops in Chad may signal the first step toward direct French intervention in the conflict.
Some of the 500 French soldiers in Chad have been sent out from the capital to other posts: including at least 150 French paratroopers to Abeche, a town toward which the rebels are moving, and a number of ''advisers'' to Salal, which is situated in the west between Faya-Largeau and N'Djamena.
At a press conference, the commander of the French forces in Chad, Col. Bernard Messana, stated that 150 French troops and three Puma helicopters are already at Abeche, which is serving as the rear base and main supply facility for President Habre's troops.
While insisting that his soldiers are for the moment acting only as ''instructors'' training Chadian troops, Colonel Messana also stated that this limited role might be ''adjusted in the future.''
In addition to the recent arrival of French troops and their positioning outside N'Djamena, Zairian paratroopers are reported to have taken up positions outside the Chadian capital.
According to Western diplomatic sources, 120 Zairian soldiers have recently moved from N'Djamena to the strategic town of Moussoro, 140 miles north of the capital on the eastern road to Faya-Largeau. Western sources also indicate that as many as 500 other Zairian paratroopers have gone to Abeche to guard the town's airstrip.
Although Moussoro and Abeche are some 100 to 150 miles south of the Chadian government's current front-line defense positions, the Zairian and French soldiers might well become involved in combat if the Libyans press farther south.
While Zaire and France are clearly taking the lead in supporting the Habre government, the role of the United States, although purely supportive, remains important.
Promising $25 million in military aid to the Habre government, the US would play a vital role in the event of an all-out confrontation with Libya by providing equipment and supplies to Chadian troops and indirectly to Zaire and France.
Chad authorities realize that although the US is insisting that the ''French take the lead'' in supporting the Habre government, the US wants to stop Qaddafi and will continue to press the French for decisive action if the situation worsens.
With the US, Zaire, and France stepping up their military commitments to the Habre government in the face of a possible showdown with Libya, a key question among Western military analysts and independent observers is the current state of President Habre's own forces, especially after their defeat at Faya-Largeau.
Initial reports from Western sources listed the number of government troops dead or missing at approximately 1,000 (out of a total government force of 3,000 ). But Information Minister Mahamat insisted that government troops and sophisticated military equipment, including the US-supplied Redeye antiaircraft missiles, had been moved of Faya-Largeau before the battle began.
The truth, Western diplomats now say, may be somewhere in between these two accounts.
Although Habre's troops began retreating before the full-scale Libyan attack, Habre's army appears to have lost at least 400 men - still a large figure given the size of Habre's forces.
As a result, Western sources here say that the Chadian government has begun a major drive to recruit new soldiers. The task of training the recruits (most of whom are either very old or very young) has been handed to French troops.
While the Libyans occupy the northern part of the country and continue to strike government positions deep in the heart of Chad, the main supporters of President Habre's government - especially the French - have finally appeared to make a commitment to stopping Qaddafi.
Whether this apparent commitment will deter the Libyan leader from continuing his military campaign in Chad is unclear. If it doesn't stop him, a confrontation between France, Zaire, and the US on the one hand and the Libyans on the other is possible.