On the Chad-Sudan border — Just over three weeks ago, Col. Radoyuane Salah Radoyuane, commander of the 10,000-strong Libyan force in Chad, staged a coup de theatre at N'Djamena airport for the benefit of French television.
Standing in front of the camera, he took a telephone call purporting to be from none other than his commander in chief, Muammar Qaddafi, ordering the immediate withdrawal of all Libyan troops from Chad.
Within minutes the first big Ilyushin jet transport was airborne, packed with military hardware and Colonel Qaddafi's red-bereted ''Islamic legionnaires.''
Colonel Radoyuane's dramatic announcement may have put an end to the controverisal Libyan presence in Chad, but it has left this desperately poor African country on the brink of open civil war.
Last Saturday in Nairobi, five African countries reaffirmed their determination to send a peacekeeping force to Chad by mid-December to fill the void left by the departing Libyans. And over the weekend, 700 Senegalese troops were reported to have arrived in the capital, N'Djamena, to join the Organization of African Unity's (OAU) first contingent, which is from Zaire.
But observers and diplomats caution that this is merely the latest attempt by Chad's neighbors to settle the bitter factional disputes troubling Chad since 1965.
The Libyans were invited in last year by the Chadian President Goukhouni Woddei when he was on the point of losing his battle against his former defense minister, Hissein Habre, now his sworn enemy. Last Dec. 15 Habre fled N'Djamena for Sudan, where he mounted an effective guerrilla operation against the Libyans in the east of Chad.
Most observers here feel that with the Libyan withdrawal, the stage is set for a decisive confrontation between Woddei, a softspoken man from the northern Toubous tribe, and Habre, who gained a reputation for ruthlessness when he kidnapped French archaeologist Mme. Claustre.
At one level, Woddei has gained in stature by the way he held his nerve through a tense two weeks and demanded the Libyan withdrawal. In addition, he has been bolstered by promises of French aid.
Despite this, many diplomats feel that Woddei has staked too much on the OAU force, which was beset by delays until Saturday's breakthrough meeting in Nairobi.
Part of the reason for the delay was expense: The United States and France are reported to be offering $12 million apiece in ''logistical'' support - but the five African neighbor states feel this is inadequate.
But a far more difficult problem is whether the OAU troops would be empowered to fight in the event open civil war breaks out again. If they are not, then the force would probably remain ineffectual - as in 1979 when Nigerian and Congolese peacekeeping troops spent a miserable three months pinned down in N'Djamena's police station between the warring factions. But if they did intervene in fighting, and Nigerians and Senegalese troops were killed, those states could get sucked into the Chadian imbroglio with serious consequences.As a result, the OAU meeting is reported to have decided that its troops in Chad will stay aloof from any fighting - but this falls short of the active support Woddei had wanted in putting down Habre.It is also clear that Woddei's troubles with Libya are far from over. Libyans troops remain firmly ensconced in Aouzou, a strip of northern Chad that was unilaterally annexed by Colonel Qaddafi in 1973 and is rich in uranium. Woddei proposes that the OAU force police this strip, but the five African states are thought unlikely to force a showdown with the Libyans over this. Indeed, some of Chad's neighbors, particularly Cameroon, feel that some continuing Libyan influence over the northern Arab-speaking part of Chad is inevitable and may be desirable as a counterweight to Nigeria.Whether or not Woddei has gained a vital breathing space by the OAU force may depend, ultimately, on the mercurial character of his great rival, Habre, whose army of 7,000 was armed and trained by Egyptian and Sudanese military officers in the border towns of Koulbous and El Geneina into an effective fighting force against the Libyans. Last week Habre's troops moved almost effortlessly to fill the void left by the departing Libyans in the east of Chad, capturing the towns of Ati, Adre, Guereda, and Abeche. Few doubt that Habre could press west to N'Djamena and catapult Chad once more into civil war. Most diplomats in Khartoum assume that Habre will bide his time and await the arrival of the OAU troops, so as not to embarass the OAU and the Sudanese. Habre's top lieutenant, Iddriss Miskine, confirmed this in an interview in Khartoum, saying that Habre would respect the OAU force ''if it is ''truly neutral and does not try to impose a solution.'' He insisted Habres forces ''are for a negotiated settlement.'' Diplomats also expect this line will be encouraged by President Jaafar Nimeiry of Sudan, who has no wish to hand the Libyans an excuse for returning to Chad. At the same time, they feel Nimeiry will do little to actively discourage Habre's drive in the east of Chad, since possession of the eastern towns will give Habre a valuable bargaining tool in any follow-up negotiations. Ultimately, however, observers are wary of making predictions about Habre, who, despite his French education, tormented the French over the Claustre kidnapping and fought French legionnaires to a bloody standstill in the streets of N'Djamena in 1978. ''Brilliant, but impatient and ruthless,'' was how one former adviser described him in N'Djamena.Whatever Habre's immediate intentions, many feel the French have made a major error by freezing him out of the frenetic diplomatic activity of the last two months.''It was not a mistake we expected of Mitterrand,'' said one analyst in Khartoum. ''It may have got rid of the Libyans from Chad. But how could he ignore the fact that Habre did more to frustrate French African policy than anyone else?''