France is sending an additional 500 troops--450 of them combat forces--to this region, it was announced today, to act as a "reserve" force to the more than 1,000 French soldiers already in Chad backing up the embattled government of President Hissene Habre in its war with Libyan-supported rebels.

French military sources said 450 paratroops would be sent to reactivated bases in the Central African Republic, which borders Chad on the south, and 50 logistical specialists would come here.

Diplomatic sources said tonight that by the end of the week, 2,000 French troops will be here and in the Central African Republic as part of France's support operation.

The announcement followed a redeployment of French paratroops closer to the frontlines in what appears to be a strong warning to the Libyan and rebel forces not to move farther south from their Faya Largeau stronghold in northern Chad, a western diplomatic source said.

While Libya has continued to pour arms into Faya Largeau since it fell to the rebels last week, French troops have moved from the base they established at the eastern town of Abeche last weekend, northward to Biltine and Arada, just south of Oum Chalouba, a town heavily bombed by the Libyan Air Force until Friday. French troops also have joined Habre's forces at Salal to the west.

Libyans continue to pour into Faya Largeau by land and air, western diplomats said today. One diplomatic source said it is unclear whether they are trying to build Faya Largeau up "to be impregnable by sheer volume of material" or as preparation for a move south.

The same sources said it was "unclear" whether the continuing Libyan arms buildup at Faya Largeau prompted the French move north of Abeche and the dispatch of the additional troops.

In other developments, Chadian Information Minister Mahamat Soumaila said that previous Libyan conditions for ending the enmity between the two countries were rejected seven months ago and, although his government is open "to any political solution," there is presently no contact between the two sides.

Western diplomatic sources said Habre regarded the Libyan conditions, delivered by the "surprise" arrival of a Libyan delegation to Ndjamena earlier this year, as a demand for the virtual handover of Chad's sovereignty to Libya and a formal ceding to Libya of Chad's Aouzou Strip, an area south of the border between the two countries that Libya occupied in 1972.

Since late June, Chad has fought a Libyan-equipped force of rebels. Both the United States and France have backed Habre's government with arms. Two weeks ago, after Libya's Soviet-made bombers began bombing and strafing northern towns held by Habre's forces, France intervened directly with paratroops officially designated as "instructors."

Since last weekend, the fighting has wound down to an undeclared cease-fire with Libyan troops and their Chadian rebel allies in military occupation of the northern third of Chad from the desert oasis town of Faya Largeau.

Egyptian Defense Minister Abdel-Halim Abu Ghazala said today that Egypt has supplied Chad with Soviet-made RPG7 rocket-propelled armor-piercing grenades and launchers, but he said that "there is not one single Egyptian soldier involved in Chad" and Egypt would send no troops, United Press International reported from Cairo.

Soumaila's remarks came in answer to reporters' questions about whether French President Francois Mitterrand's government had notified Chad that an unofficial envoy was sent by France to Tripoli, the Libyan capital, to seek a peaceful solution to the conflict. Soumaila said it was not for the French government to notify his government but he said the solution to the conflict lies in Tripoli.

While there is no direct contact between Chad and Libya at present, Soumaila said, "we are still available to any political solution."

The original Libyan conditions for better relations between Habre's government and that of Libyan leader Col. Muammar Qaddafi are that:

* Chad declare itself an Arab Islamic republic and join the Arab League.

* Libya and Chad agree to a mutual defense treaty.

* The two countries' "traditional" borders remain as they are, meaning Chad would drop its demands for return of the Aouzou Strip.

Habre responded that Arabs make up a very small part of Chad's population--13 percent--and a country such as Chad, with a population of 4 million--half Moslem and the other half Christian and followers of traditonal African religions--should remain a secular state.

Habre said the mutual defense treaty Libya proposed would give Libya control of Chad. He said there would be no compromise on Chad's demand for the return of the Aouzou Strip.