US feels pressure to give military assistance to Chad. As fighting between Chad and Libya continues, the US and France look anxiously on. In Washington, the debate is over sending Stinger missiles to Chad.

Fighting between Chad and Libya over a strip of desert borderland is taking on new intensity with the first major battle inside Libya and an attempted air attack on Chad's capital last weekend. Official and other observers in Washington had expected the war might spread into Libya, sparking new pressures on France and the United States to support Chad more actively. One of the decisions Washington is wrestling with is whether to supply Chad with portable antiaircraft missiles called ``Stingers'' for use against Libyan planes in the north of the country. During the weekend, Chad's troops routed a Libyan column apparently inside Chad and chased it back to its base in Libya - the first major Chadian penetration of Libya in this long border dispute. Chad's troops reportedly captured the Libyan base, Matan as Sarra, and set about destroying the aircraft and other materials in place. This base had reportedly been used in Libyan bombing attacks on Chad since the new round of fighting began in early August.

In response to Chad's actions Libya launched new air raids inside Chad, further south than their attacks earlier this month. An attempt to strike N'Djamena, Chad's capital, sparked the first overt response in this round of fighting by the 1,200-man French military mission in southern Chad. French forces shot down a Libyan bomber and sent several jets up to intercept other Libyan planes.

France has told Chad's President, Hissein Habr'e, that he is on his own in trying to retake by military force the disputed, 44,000-square-mile Aozou strip and has urged him to seek international mediation. However, senior French officials repeated again this weekend that France remains committed to defending ``Chad's territorial integrity'' and to responding militarily to any attack south of the 16th Parallel. France had hoped to maintain a low profile in the current fighting.

Libya has strongly protested the French shooting of its plane and charged France and the US with direct participation in the conflict. Libyan threats that those aiding Chad could be ``burned'' have raised prospects of Libyan sponsored terrorist attacks.

The new developments in the war may force a reticent France to play a more active role in the fighting, particularly if Libya continues to hit areas that France has pledged to defend. Washington also feels pressure to show its support for Chad, officials say.

Although US officials refuse to comment directly on any US decision to provide Stingers, sources in and out of government explain that Chad has sought the Stinger so it can strike Libyan aircraft flying at higher altitudes and with shorter in-range profiles than their US ``redeyes'' and Soviet SAM 7-2s (captured from Libya) can hit. These sources say Libya had taken advantage of its dominant air power and the long supply routes for Chad's forces to stage repeated high-level bombings of outposts in the north of Chad and to recapture the village of Aozou on Aug. 28, three weeks after Chad took it in daring Jeep-led attack.

Outside observers and US officials see more involved than two small states squabbling over a few miles of sand.

On one level, Mr. Habr'e, a black African leader, is standing up to Libya's quixotic Muammar Qaddafi. Colonel Qaddafi has used his wealth and military might to influence events in surrounding countries, often by support for subversive elements, and to support terrorist and liberation movements around the world, officials say. Yale Prof. William Foltz, who just returned from Chad, explains that Chad's Habr'e is unswervingly dedicated to regaining the Aozou strip, which falls in his home region. With a skillful mix of military victories and domestic reconciliation, Habr'e has brought a degree of unity and national spirit to Chad unknown in the 20-odd years of civil war that have devastated the country, Dr. Foltz says.

Many officials and specialists here believe a Habr'e victory would send an important signal to neighboring countries about Libya's vulnerability and reinforce Chad's nascent unity. But Georgetown University's Henry Schuler says that US officials are sensitive to the danger of making Habr'e's victory appear too dependent on big-power help if Stingers are provided. Foltz adds that it appears the Stingers would help Habre's forces but not be a ``panacea.''

On another level, there is a complex dance going on between France, the US, Chad, and Libya. Chad's former colonizer, France, is also its major arms supplier and provides an air shield for most of the country. But it is a love-hate relationship. France is committed to preserving Chad's integrity, but is often infuriated by Habr'e's determination to push hard and fast to evict Libya militarily from all of what he sees as Chad's territory. Chad, for its part, is grateful for French support, but angry that Paris is not more forthcoming.

France has its own interests in mind also. Foltz says France, not the US, has the long-term commitment to aid Chad and thus has a strong interest in finding a political settlement that avoids a costly, prolonged border war. Washington recognizes France's key role and wants Paris in the lead, Foltz and US officials say. That is one of the reasons the US has hesitated to give Chad Stingers, they add.

Simultaneously, France would like to maintain the option of a better relationship with Libya, because of its long-term interests in North Africa and for shorter-term reasons. For example, Libya is one of the few countries that still has an open line to Iran and to some of the hostage holders in Lebanon. Some in Washington believe that Paris may have been trying to find a diplomatic solution in Chad in part to enlist Qaddafi's help in France's current face-off with Tehran and in efforts to free its hostages in Lebanon.

Schuler adds that, though the war in Chad was not popular in Libya, Libya's claim to the Aozou strip is widely accepted, even by anti-Qaddafi dissidents. That claim is based on a signed, but never ratified, 1935 treaty between the colonial powers - France and Italy. Qaddafi disowns a 1955 treaty between Libya and France, which apparently recognized the Aozou strip as Chad's, and says he secretly bought the land from a President of Chad in the early 1970s. France says the dispute should be settled by international arbitration; the US recognizes Chad's claim, because that was the internationally recognized border at independence.