Rene Journiac, the discreet shadow of France's still considerable power in Africa, died in an airplane crash in Cameroon, it was announced here today.

The plane, piloted by a nephew of Gabonese President Omar Bongo, was lost last night with all aboard in the mountains of northern Cameroon. The others included a French lieutenant on assignment to Gabon and two other Gabonese crewmen.

Journiac, 58, had just finished a successful mission to Chad, where he had persuaded rival factions, who seem to be on the verge of renewed civil war, to rescind a request for the withdrawal of the French troops that have been the country's shield against Libyan intervention.

Journiac's title of technical conselor to the president was a transparent camouflage for a man who, as Valery Giscard d'Estaing's man for Africa, rivaled the French foreign minister in importance.

Loss of his special knowledge and personal relations with African leaders is a major blow for France just as it appeared necessary for the French to strengthen opposition to Libyan moves in French-speaking Africa.

The Elysee Palace discouraged speculation that Journiac had been assassinated. An Elysee spokesman said, however, that there would be a special investigation of the crash of the Gabonese executive jet.

The Elysee explained the delay in announcing the deaths by the time it took for search teams to reach the plane.

It was bound from Ndjamena, the capital of Chad, to Yaounde, the capital of Cameroon, where Journiac was to meet Cameroon President Ahmadou Ahidjou before going to Gabon to see President Bongo.

Recently at the Elysee Palace, a president staffer called a visitor to the window to see "the most powerful man in Africa." Zaire's President Mobutu Seso Seko was getting out of a car to call on Giscard. The Elysee staffer did not point to Mobutu but to the man greeting him on the steps -- Journiac.

From 1967 he was the deputy and, in 1974, the successor of Jacques Foccart, Charles de Gaulle's personal spymaster, a man who oversaw France's interests in Africa, and its remaining overseas possessions, the work of French intelligence services and the finances and strongarm squads of the Gaullist party.

Journiac was described by those who dealt with him as mild-mannered, scholarly and apparently incorruptiable. He was said to have a facility for establishing good personal relations with African leaders who oppose French policy and for maintaining relations with African opposition leaders.

One of the problems he reportedly was working on most intensively was trying to prepare smooth successions to the aged Felix Houphouet-Boigny of Ivory Coast and his fellow French-speaking African elder stateman, Senegal's Leopold Senghor.

Self-effacement and discretion were the overriding characteristics of Journiac, who virtually never spoke to journalists.

He personally delivered the ransom money to rescue French ethnologist Francoise Claustre after she was held for 33 months by the Libyan-backed Chadian rebel leader Hissen Habre, now Chad's defense minister thanks to a Journiac-directed maneuver.

When pressure build up against Bokassa, the self-styled emperor of what once again is known as the Central African Republic, Journiac met him in Gabon in the presence of the Frenchman's close friend, President Bongo. By all accounts, Bokassa lost his temper and struck Journiac with his cane, a blow that probably sealed Bokassa's fate.

The emperor was able to escape before France sent in troops, but spent an embarrassing weekend sitting in a plane at a French air base, demanding asylum.

Journiac was known as a "one-man show" who kept "everything in his head, nothing on paper" as one observer put it. That alone will make it hard for Giscard to replace him.

Ironically, Journiac's career ended where it started, in Cameroon, where he was a judge in the French colonial administration.