PARIS (AP) _ Chad said Libyan forces today bombarded the embattled Tibesti Mountain town of Zouar, and France vowed it would continue to respond to Libyan attacks on southern Chad with ''firm ripostes.''

French warplanes raided Libyan installations in northern Chad on Wednesday. France and Chad reported a Libyan air raid hours later on a government post in southern Chad, but Libya today denied making the attack.

The government in N'Djamena, the Chadian capital, said the northern town of Zouar came under ''savage'' bombardment early today. The government statement did not specify what kind of firepower the Libyan forces used, but it made no mention of warplanes.

There was no immediate report on casualties in the attacks.

The Chadian government claimed it beat back a Libyan attack on Zouar on Saturday.

Zouar, about 570 miles north of N'Djamena, has been the scene of several attacks and counterattacks during the past three weeks. The Chadian government claimed to have killed more than 400 Libyan troops in a victory there Dec. 20. N'Djamena has charged Libya with using napalm bombs and toxic gas in the several attacks in the Tibesti.

French Premier Jacque Chirac's office said Libyan planes Wednesday attacked Kouba-Oulanga, 40 miles south of the 16th parallel that divides southern Chad, controlled by the government of Chad President Hissene Habre, from the rebel- held north.

Ninety minutes earlier, French Jaguar jet fighters raided Libyan installations in northern Chad in retaliation for another Libyan air raid Saturday. France said it was trying to demonstrate its might and head off an escalation of the conflict. Chad, Libya's southern neighbor, is a former French colony. Libya claims a sector of northern Chad.

Libya's official JANA news agency today denied it raided southern Chad on Wednesday, and said, ''These reports are mere lies and fabrications which come within the context of the campaign of misrepresentation and deceit of information.''

JANA was monitored in London by the British Broadcasting Corp.

Denis Baudouin, a spokesman for Chirac, said today in response to the JANA report that the Libyan attack ''clearly took place and it was rather minimal.''

He also said, ''We will continue to make graduated and firm ripostes, but we don't want an escalation.''

The French attack Wednesday targeted the Libyan desert base at Ouadi-Doum, north of the 16th parallel. Paris said its warplanes ''neutralized'' Libyan radar installations.

France, which has 1,400 troops in Chad, established the 16th parallel in 1983 as a demarcation line beyond which Libyan-backed Chadian rebels trying to topple the government of President Hissene Habre should not venture. It has maintained a policy of responding to Libyan aggression in southern Chad with air strikes in the north.

France attacked the fortified Libyan airstrip at Ouadi-Doum, 550 miles north of N'Djamena, on Feb. 16, 1986. The Libyans replied the next day with a raid on the airport in N'Djamena.

Until recently, Libya and Chadian rebels backed by Libya maintained near total domination of northern Chad. However, the main rebel group, headed by Goukouni Oueddei, defected to the government side this fall after Goukouni was reported wounded by his Libyan guards in Tripoli. He remains in the Libyan capital under house arrest.

Libya, estimated by Western intelligence to have 5,000 to 7,000 troops in Chad, now holds its positions with the backing of scattered rebel groups.

Fighting between Chadian and Libyan forces in northern Chad has intensified in the past month. On Dec. 16, France parachuted supplies to former rebels now loyal to the Chadian government and announced, along with the United States, that it was stepping up assistance to Habre.

White House spokesman Larry Speakes said: ''We have expressed general support for the French role in Chad and we continue to do so in this case.''