Retreat from Chad seen as humiliating defeat for Libya leader. Chad's Habr'e now has opportunity to end two decades of civil war

The retreat of Libyan troops from the last major military base in northern Chad is both domestically and internationally humiliating to Col. Muammar Qaddafi. Rather than risk a second crushing defeat in a few days, some 3,000 Libyan troops are retreating from Faya-Largeau, the last major Libyan military base in northern Chad, according to informed French and United States sources.

The retreat marks the virtual collapse of the Libyan occupation of northern Chad in support of a rebel insurgency there. And it means that President Hissein Habr'e is close to reunifying the country - a step his nation, one of the poorest in the world, will welcome.

The Chadian war has never been popular with either the civilians or the military in Libya. Colonel Qadaffi's credibility and prestige will almost certainly suffer as news of the heavy Libyan casualties and military defeats filters through to the Libyans.

The military defeats in Chad are also seen as a humiliating regional setback for the Libyan leader's plans to expand his borders and create an Islamic empire owing allegiance to Tripoli.

The fall of Faya-Largeau, Mr. Habr'e's hometown, is symbolically important. A strategic crossroads commanding the main route south to the capital N'Djamena, it was captured by Libya nearly four years ago.

The fall Sunday of the Wadi Doum air base, 100 miles to the northeast, left Faya without air cover and deprived of its main supply source.

Although defended by some 4,000 heavily armed Libyan troops, Wadi Doum fell after only two hours of fighting. Libya lost some 1,300 troops and a large amount of equipment, according to top-level Chadian officials.

The Chadian forces were expected to follow up their success by encircling Faya-Largeau for a final attack. But the Libyans began to blow up fuel and ammunition dumps Tuesday night before starting the evacuation Wednesday, according to French sources.

The fear of Libyan air attack was the main factor detering Habr'e's troops from retaking the oasis town.

The long Libyan column of some 300 vehicles will probably be pursued and harassed by highly mobile and quick-striking Chadian troops, military analysts say. The Libyans are expected to make for Aozou located in the Aozou Strip - a 1,000-mile band of reportedly uranium and mineral rich Chadian territory adjoining Libya's southern border annexed by Libya in 1973.

The Chadians may decide to maintain the military momentum by carrying the offensive into the Aozou strip, the analysts say. However, this would dangerously stretch their supply lines while running the risk of air attacks launched from bases in southern Libya.

The Chadian military successes have been scored without direct French intervention, French Defense Minister Andre Giraud stressed. The estimated 2,400 French troops in Chad have not crossed the ``red line'' - set by France in 1983 along the 16th parallel to divide the Libyan-controlled north and the Chadian-controlled south.