The stationing of crack French paratroops in the remote northern Chad oasis of Salal will relieve not only Chad President Hissein Habre but moderate pro-West nations in the region, too.
It means that the Libyan-backed forces of rebel leader Goukhouni Woddei risk fighting the French if they want to sweep further south toward the capital, N'Djamena.
West African moderates had been concerned by France's apparent reluctance to defend its former colony against Libyan-backed rebels. Several of Chad's neighbors are also former French colonies, and have become alarmed at Libyan leader Muammar Qaddafi's inroads south of the Sahara. They view Qaddafi's intervention in Chad as a threat to regional stability and wondered if France would defend them if they were faced with an invasion.
Ivory Coast's President Felix Houphouet-Boigny, said recently, ''Part of Chad has been annexed by another OAU (Organization of African Unity) member. We cannot accept that.''
Senegal's President Abdou Diouf said last week, ''We must stop the Chadian adventure, otherwise we shall see it repeated in other countries.''
Senegal, which broke diplomatic relations with Libya in 1980, strongly opposes any redrawing of Chad's frontiers. ''If this facile solution is adopted, it marks the end of the territorial integrity of all African countries,'' Diouf warned.
Zaire's president, Mobutu Sese Seko, who has sent 2,000 troops to Chad to support the Habre regime, said, ''Chad must count on its friends to restore its territorial unity'' threatened by ''this act of Libyan aggression.''
There hare many reasons why France's Socialist government has been reluctant to send troops into Chad. Francois Mitterrand and the Socialists, who came to power in France in May 1981, have wanted to drop the role of ''African gendarme, '' with its colonial overtones.
In addition, for many years Habre fought French-backed Chadian governments. He also has a reputation as the most ruthless of Chad's rebel leaders. The French still remember his year captivity of two French anthropologists for two years in the mid-1970s.
But Chad is a former colony and is regarded as geopolitically important. Chad could provide Qaddafi with a base from which to pursue his dream of creating an Islamic Saharan empire stretching from Mauritania to Sudan. Most countries in the region are desperately poor and politically vulnerable.
Chad's western neighbor, Niger, is the most immediately threatened, according to analysts. Recent university riots in the capital, Niamey, reflect growing social unrest due to mounting economic difficulties linked to the depressed world market for uranium, Niger's main export.
And the pro-Libyan coup in Upper Volta on Aug. 4 has increased fears of regional instability, especially in the Ivory Coast. During a prolonged teachers' strike last April, Ivory Coast President Houphouet-Boigny accused an unnamed foreign power - understood to be Libya - of seeking to destabilize the country.
Qaddafi was at that time visiting Benin, where he infuriated the Ivorian government by declaring ''We must continually incite the African peoples to revolution and the Army to take power.''
The Ivorian press branded Qaddafi as an ''Arab-African Hitler.''
Ivorian sensitivity is due to the worsening socio-economic situation. Three years of recession and a stringent austerity program outlined by the International Monetary Fund have caused unrest among the educated elite and tarnished the country's image as a model for Western free enterprise development policies.
Until recently, the conflict in Chad has been widely regarded as an obscure African civil war reflecting the absurdity of artificial, colonially drawn frontiers.
A tangle of tribal chieftans has battled for control of the sparsely populated country of 4.5 million people for the past 17 years. The endless fighting has ravaged the economy, already one of the world's poorest where per capita income is about $240 a year.
Officially, French troops have been sent to Salal to instruct Habre's forces on how to use French military equipment, which recently was flown in there. But the French commander in Chad, Col. Bernard Messana, has said, ''We shall defend ourselves if attacked.''
Zaire's president, Mobutu Sese Seko, who has sent 2,000 troops to Chad to support the Habre regime, said, ''Chad must count on its friends to restore its territorial unity.''
The Chadian armed forces weekly, al-Watan, has described France's hesitation to provide support as ''a mixture of hypocrisy, impotence, and cynicism.''