France has decided to reinforce its contingent in the Central African Republic to reassure France's African friends after announcement of an arms-backed merger of Libya with Chad, French Defense Ministry officials said today.

The decision came at the request of former African colonies with which France maintains defense or military cooperation agreements, the officials said.

They refused to provide further details, except to say that both air and ground forces would be sent to the Central African Republic, which is just south of Chad. Informed sources said the fresh forces would be sent to Bouar, a major base in the northwest.

While the French government refrained from making any formal announcement of the reinforcement, officials seemed eager to confirm the report as the government multiplied reassuring gestures toward its former colonies in western and central Africa. They reportedly have been shaken by the French failure to act against the Libyan-spearheaded military takeover in mid-December of the Chadian captial of Ndjamena, followed this week by the step toward a potentially menacing merger between Libya and Chad.

France already has about 1,000 troops in the Central African Republic, stationed there since French paratroops overthrew emperor Jean-Bedel Bokassa in 1979. While French President Valery Giscard d'Estaing's complicated relations with Bokassa undoubtedly were an important factor in the decision to oust the emperor, he apparently sealed his fate by offering Libyan facilities like the strategically located Bouar base in exchange for financial support after Paris tried to pressure him with an aid cutoff.

It appears that the circumstances of Bokassa's overthrow served both to raise African expectations that France would continue to act as a shield against Libyan expansionism and also to hinder Giscard's ability to carry out the policy.

Political accusations here, that the scandals surrounding the Giscard family's complex web of relations with Bokassa symbolized the excessive personalization of France's African policies, apparently complicated the French decision-making process in an election year.

The poisoned atmoshpere in Paris surrounding the African policy, traditionally a key part of the "reserved domain" of the French presidency, made Giscard appear vulnerable to criticism for practically any action he conducted in Africa. Newspapers like the influential Le Monde that had been highly critical of French interventionism in Africa expressed even louder criticism of the president's failure to stop the Libyan advance.

French government attempts to accommodate Libya's mercurial relations with Paris had met with growing resistance to what some officials privately call the "Libyan lobby" in the Giscard entourage.

News leaked of French oil-prospecting contracts with Libya. The timing made the contracts appear to be a Libyan payoff for French inaction in Chad. Those who charge France with seeming to appease Libya then argued that the policy was beginning to endanger France's more important interests in Africa.

Several commentators suggested that France's traditional African friends might be forced to turn to the United States for protection if they could no longer count on France.

In an election year, the prospect of Giscard's Gaullist rivals in the government coalition accusing him of ceding to the United States the late president Charles de Gaulle's legacy of leadership in French-speaking Africa has broad implications.

The Gaullist party organ, La Lettre de la Nation, said France had "lost face" in Africa. "This has become a custom, but a custom so unbearable that it could be very costly for the man who imposes it upon us," it added.

The news of the French reinforcements in the Central African Republic thus are seen here as a signal to the Africans that the paralysis of decision in Paris is ended. At the start of an official visit to the Ivory Coast, the richest former French colony in black Africa, French Foreign Minister Jean Francois-Poncet said: "Where security is concerned, Africa should know that, whatever the source of a threat, it will find France at its side today as before."

France already has 450 soldiers and airmen stationed in the Ivory Coast, 500 in Gabon and 600 in Senegal. There are also French paratroop battalions in Djibouti in the Horn of Africa and in Comoro Islands in the Indian Ocean.

Giscard held a council of war on security in Africa yesterday with his principal military and African affairs advisers. Such meetings in the underground war room of the Elysee Palace normally are kept secret. But this meeting was announced and prominently reported on state radio and television.

It was followed up by a French Foreign Ministry communique saying that the merger between Libya and Chad "reveals ambitions that constitute a threat for the security of Africa."

French diplomats earlier had said they were struck by the virtual silence of the African states on the merger. They now suggest France can take some credit for subsequent criticisms by Nigeria, Egypt, Sudan, Morocco, the state-controlled press of the Ivory Coast and Senegal, and the call for an emergency meeting on Chad by the Organization of African Unity.