Francois Mitterrand, an Africa hand for the past three decades, set off yesterday on his first presidential trip to France's former sub-Saharan colonies in an oddly apologetic mood.

"I am not trying to distance myself from former French policy," the Socialist leader told government-owned Radio France International in an apparent effort to reassure the heads of state of France's one-time African empire that the current French government will not upset France's traditionally close ties to Africa.

That Mitterrand--a man highly trusted by his African peers--felt so constrained underlined the lingering doubts about his Socialist Party colleagues.

In some African capitals--and among a sizable percentage of the News Analysis 250,000 French citizens living in Africa--the Socialist victory a year ago had caused concern that France was about to abandon the friendly rules that had governed their relations for the first two decades of French-speaking Africa's formal independence.

Indeed the week-long visit's three major stops to Niger, Ivory Coast and Senegal were chosen carefully to symbolize less the change that Mitterrand promised French voters at home than the continuity and protection the African presidents so crave.

Mitterrand said Thursday in Niamey, Niger, that France would honor defense pacts it had undertaken to ensure the security of its friends in Africa and strengthen them if necessary, Reuter reported.

In the immediate wake of the Socialist victory, Africans and French citizens interested in Africa were frightened by what was perceived as the newcomers' zealous morality and desire to put France's relationships with Africa on a less indulgent basis.

French officials expressed determination to put French aid to Africa--which will continue to receive the lion's share of French largesse--on a more cost accountable footing. The Socialists made no secret of their desire to stop subsidizing presidential slush funds in Africa thinly disguised as development projects.

"The Socialists started out looking like dead ringers for the Carter administration in its early days," a Western diplomat said, "what with their concern for human rights, a desire to establish and develop contacts with leftist regimes and a refusal to countenance the worst excesses of some regimes protected by French governments in the past."

That is not the image that Jean-Pierre Cot, minister of cooperation and development, and his aides have of themselves.

"On the contrary," an aide said, "the first thing we did on taking office was to figure out what the Carter people had done wrong and make sure we did not duplicate their errors. We have no desire to destabilize Africa."

Cot dismissed suggestions that France reduce its 9,000-troop military presence in Africa, almost half of which is stationed in the strategic Indian Ocean port of Djibouti. But the government also decided that henceforth French troops--and the once omnipresent secret services--would intervene solely to protect French lives, no longer to prop up tottering governments.

"We made it clear we were not going to carry out left-wing 'Barracuda' operations," an aide to Cot said, alluding to the code name for the French military intervention that overthrew Emperor Jean-Bedel Bokassa of the Central African Empire in 1979.

Noting former conservative president Valery Giscard d'Estaing's propensity for activism in Africa, which prompted him to dispatch troops to Zaire in 1977 and 1978, the aide said, "We are not going to be the Cubans of the West."

Initially Cot purposely gave a cold shoulder to Zairian President Mobutu Sese Seko and postponed until this September the Franco-African summit conference that had been scheduled for Kinshasa last fall. Cot finally visited Zaire this month--on his 24th foreign trip--to help out Zaire's parlous finances. There is still little warmth among French officials for Mobutu or the corrupt government he heads.

Such moralizing has not been universally appreciated.

Although Cot elsewhere moved slowly to correct what he perceives as past French overinvolvement in the active administration of some black African governments, he angered Gabon's President Omar Bongo by removing the French ambassador, Maurice Robert.

Robert, a former colonel in France's overseas intelligence agency, was replaced in keeping with the Socialists' desire to sanitize the Foreign Service and end some African leaders' propensity for demanding that France name the Africans' choices as ambassadors.

African leaders--and the influential lobbies representing extensive French private interests in Africa--made known their displeasure with Cot.

But as in the past, French African policy continues to be made by the president, the foreign minister, the president's African affairs specialist--now a dentist named Guy Penne--and the Cooperation and Development Ministry.

Accustomed since independence to first-class, personalized treatment by successive French presidents, the African leaders long have enjoyed their special relationship with the Elysee Palace's African expert.

"Penne is the good cop, and we are the bad cop," a Cot aide explained. "He tries to wheedle more money for his clients when we turn down their more outlandish projects."

Despite occasional policy differences--often seeming to involve Socialist Party interference--the tandem appears to have functioned smoothly in its first year.

Its most notable success was in helping to arrange the withdrawal of Libyan troops from Chad last fall.

"When we first told the Americans we thought Chadian President Goukouni Oueddei could be persuaded to ask the Libyans to withdraw their troops," the Cot aide said, "the Americans thought we were Carter softies. To them it must have seemed as if we thought Babrak Karmal would ask the Soviet troops to leave Afghanistan and that they would comply."

When Libya did withdraw its troops from Chad, "our credibility soared in Washington" and French-American relations are termed excellent by officials of both countries.

That success wiped out American anger with France for honoring the previous government's arms deals with Libya.

French officials believe their policy has been successful. Although Chad may continue to suffer through a longer period of instability, for the French the primary concern is keeping it from becoming a battlefield for East-West tensions or Libyan interference.