Paris — Now that Libya's Col. Muammar Qaddafi controls the entire northern desert of Chad, French officials are hoping he has captured all he wants and is ready to deal.
But this weekend as Libyan planes bombing the strategic town of Oum Chalouba farther south, concern mounted here that Colonel Qaddafi is preparing to send his troops forward.
If he does, the French are making it clear that the Libyans will have to take on the troops they sent to Chad last week. Over the weekend, some 150 of the 500 French paratroopers in Chad were dispatched to the key eastern town of Abeche. A smaller squadron was ordered to Salal, north of N'Djamena.
''If we are attacked, we will defend ourselves,'' the commander of the French troops, Col. Bernard Messana, said, in announcing the deployments.
Despite this clear warning to Qaddafi, French officials continue to describe the paratroopers as ''communications experts'' whose mission is primarily to process information from American AWACS planes - and steer clear of the fighting. But the troops obviously can do much more than that.
Picked from elite units specially trained for intervention in African conflicts, they are similar to those used in France's lightning raid on Kolwezi in Zaire several years ago. They are heavily armed with modern antiaircraft and antitank weapons, and their deployment at Abeche and Salal provides a defensive line across the center of the country.
Militarily speaking, the key question is whether the French will follow up their commitment of troops with air support. Following the fall of the northern town of Faya-Largeau last week, a growing number of officials here say the only way to save the government of President Hissein Habre is to send in French jets to end Libyan dominance of the air. Habre has been demanding just such intervention for more than a month, and last week President Reagan seconded the motion.
With eight Jaguar fighter bombers and 10 Mirages based in Africa, the French already have the necessary airpower in the region. So far President Mitterrand has refused to commit them to the Chad conflict, but Defense Ministry officials say the planes could go into action almost immediately, if and when Mr. Mitterrand makes the decision to use them.
That decision will depend on what Qaddafi does next. If he moves south, threatening French troops, the consensus is that Mitterrand could no longer avoid sending his planes, even though this would mean another big step in the escalation of the conflict.
But the French are still hoping things will not come to this. The dominant analysis at France's Ministry of External Affairs seems to be that Qaddafi will not want to take on the French, but instead will stop and negotiate.
Support for this view comes from a dispatch that ran late last week on the Libyan news service, JANA. The Libyans said ''initiatives had been made to produce a peaceful solution in Chad,'' and that ''France would play a major role in any new arrangements.'' The Libyans also interpreted the French dispatch of paratroopers to the country as a sign that Paris would like to dump Habre.
French Foreign Ministry officials said they didn't know what initiatives the Libyans were referring to, and they repeated their country's support for ''the legitimate government'' of Habre. Privately, though, French officials said they had an idea that Qaddafi was putting forward a feeler in the direction of a de factom division of Chad.
Such a division would have Libya maintain a preponderant role in the north while France would have its influence in the south. The French feel they have to reject any such proposal, because it would violate the principle that borders from colonial times should not be changed. If borders were changed along tribal or religious lines, the officials say, most of Africa would have to be split up.
Nevertheless, there is a growing sentiment here that just such a division may be the best possible outcome. For the French, the Chad problem has been a recurring nightmare: Since independence in 1960, the French Army has been forced to intervene repeatedly to restore order, only to leave and find the country's different factions soon at war again.
President Mitterrand is reportedly said to think that Chad is irreparably split by economic, ethnic, and religious divisions. He is also said to believe that since the basic split is between the north, which is Muslim, and the south, which is Christian or ''animist'' (although both regions have dozens of opposing parties, tribes, and interest groups), a partition into two countries makes some sense.
But Mitterrand is not going to cede northern Chad to Qaddafi or Chadian rebel leader Goukhouni Woddei easily. France is concerned about giving Qaddafi control of an area with significant uranium deposits.
More pressing is a desire to stop Qaddafi from creating a loose kind of sub-Saharan Muslim empire. His designs frighten Egypt, Sudan, West Africa's moderate Francophone leaders, and the US. All have pushed France to intervene. A reluctant Mitterrand finally succumbed to such pressure because of his overwhelming desire to protect his country's influence with its former African colonies. As the US administration stepped up its aid to Habre's government, the French were becoming concerned that the US might replace France as Africa's favorite protector.