France issued a strong warning to Libya today against further military intervention in the civil war in Chad amid reports here that the French are preparing to intervene against the Libyan advance.

French officials, who had been playing down the Libyan presence in the landlocked central African country, have only recently started echoing earlier U.S. government statements that there are 4,000 to 5,000 Libyan troops operating in the former French colony.

French officials are saying for the first time that Libyan leader Col. Muammar Qaddafi has been proposing what amounts to a north-south partition of Chad between Libya and France.

Today's unusually solemn warning from the Elysee presidential palace seems not only to exclude the possibility of any deal but also apparently is preparing French opinion for renewed French involvement in the troubled territory. Chad, which borders on six other African states, has been beset by complicated civil strife among its 11 officially recognized armed political parties.

The force of the Elysee Palace statement was strengthened by being issued hours after publication of a highly detailed report in the Paris daily newspaper Liberation that three French paratroop battalions based in Cameroon, Central Africa and Djibouti would converge on Chad starting Monday.

There was no public official denial of that report, although French diplomats privately expressed doubt that President Valery Giscard d'Estaing would risk the involvement of the forces in land battles. But the sources did not discount the possibility that a squadron of four Jaguar ground-attack bombers recently flown to nearby Gabon might fly into action against the Libyans, whose Soviet tanks have been seen in battle for control of the Chadian capital of Ndjamena across the river from Cameroon.

As the French presidential election campaign approaches, Giscard has been widely accused by the Gaullists, his nominal coalition partners, of being weak and indecisive in foreign policy, especially against the Soviet threat. Some French officials privately note that Qaddafi's intervention provides a perfect opportunity for Giscard to counteract that electoral argument by showing French power.

France, the Elysee communique said, "is gravely preoccupied by the new deterioration of the situation . . . resulting from the intervention of armed foreign elements. France warns against the continuation of that intervention . . . that threatens the stability of the region. France will support any collective effort that the African states may undertake to reestablish peace in Chad, preserve its unity and maintain its independence."

The Elysee communique made it clear that any French action would be presented as coming at the request of other African states. At French urging, several normally cautious states in French-speaking Africa, including Niger and Cameroon, have recently joined the already insistent chorus of countries that have denounced Libyan activities in Chad and in West Africa.

Senegal, Ghana and Gambia have recently broken diplomatic relations with Libya. Gabon's President Omar Bongo today welcomed the French warning to Libya and said it should have come sooner.

France until recently has been inhibited by the reserved attitude of Nigeria, Chad's most important neighbor and Africa's most populous country. French Cooperation Minister Robert Galley told correspondents this week, however, that the Nigerians have grown increasingly disturbed by unauthorized visits to Moslem northern Nigeria by Libyan officers recruiting for Qaddafi's Islamic Legion. The legion is a force composed of black Africans and Arabs and is said to have 1,500 men in the Libyan contingent in Chad.

Nigerian President Shehu Shagari this week warned visiting Libyan Foreign Minister Ali Triki that Nigeria could not tolerate this situation.

The French have also been hampered because Libyan forces are legally in Chad in response to an appeal by Chadian President Goukouni Oueddei under an accord he signed with Libya in June, a month after French ground forces that had been keeping the rival factions apart were withdrawn from Chad at the leader's request.

The main force battling Goukouni for control for the capital belongs to Defense Minister Hissene Habre, who is supplied by Egypt and Sudan. Not only is it a problem for the French to go into action against the legally recognized president, but it is also difficult for them to support Habre, who has a reputation of being anti-French. The French Army accuses him of having personally cut the throat of a French officer his forces had captured when it was Habre's group that was allied with Libya and Goukouni's with France.