A clearer picture emerged today of the role of French fighter planes in the first significant fighting to take place in Chad since France's military intervention last month.

Reports from Paris and the Chadian capital of Ndjamena suggested that, despite earlier French denials, the French Jaguar planes helped intimidate several hundred Libyan-backed rebels by low swoops over their positions. But the planes, whose formal role in Chad is to protect the French troops, estimated by sources in Chad to approach 3,000, did not drop bombs or fire shots as claimed by spokesmen for the rebels.

Senior officials in Paris took pains to play down the significance of the fighting, which took place to the north of what is known as the "red line" along the 15th Parallel that is being defended by the French expeditionary force from Salal in the west to Abeche and Arada in the northeast. They depicted the incident as a minor skirmish between rebel forces loyal to former president Goukouni Oueddei and government troops rather than the start of a major new Libyan-led offensive.

There are, however, enormous problems in evaluating information from Chad because official statements from all sides in the conflict are a compound of half-truths, lies and deliberate attempts to mislead. Independent accounts of the fighting are practically nonexistent since western reporters are barred from leaving Ndjamena and denied access to French bases.

Friday's fighting around Oum Chalouba, which is little more than an uninhabited crossroads in the desert, is a case in point. The government of President Hissene Habre claimed its troops had beaten back an attack by about 3,000 Libyans and mercenaries. Rebel spokesmen insisted their forces had been repeatedly bombed by French planes. The French acknowledged only that the Jaguars had taken part in a routine "reconnaissance" mission above French lines.

The most reliable reconstruction of what actually happened appears to have come in an Associated Press dispatch from Ndjamena today quoting "western"--presumably American--military sources as saying three Jaguar fighter bombers staged a 30-minute mock dive-bombing attack on approximately 1,000 rebels who then fled into the desert.

This account agrees with a statement by French Defense Minister Charles Hernu that the Jaguars did not engage in any firing--a more circumspect claim than that advanced by the French military spokesman in Chad who explicitly denied that the Jaguars had intervened in any way.

French President Francois Mitterrand has made clear that his troops will not support Habre in any attempt to reconquer the north. But he has also warned that, if the French paratroops are in any way threatened by the Libyans, they will not merely defend themselves but retaliate with all available means.

Officials in Paris believe the Habre government deliberately exaggerated the importance of the rebel attack on Oum Chalouba to encourage the French forces to play a more active role. Since their arrival in Chad on Aug. 14, the French have managed to keep out of the actual fighting.