While expanding its military presence in Ethiopia and other embattled parts of Africa, the Soviet Union has suffered quiet but substantial ideological set-backs here in West Africa in recent months.

The most dramatic reversal has been made by Guinea's mercurial and radical president,Sekou Toure, who appears to be moving toward ending a decade of regional isolation and dependence on the Soviets by mending his fences with his pro-Western neighbors, the Ivory Coast and Senegal.

Through them, Sekou Toure is trying to reach the West.As one sign of his new sincerity, he has cut back on Soviet naval operations out of Guinea's capital and port city, Conakry, and has placed restrictions on Soviet reconnaissance flights operating out of or over Guinea, according to informed Western sources in Africa.First hinted at six months ago by Sekou Toure's unexpected public tribute to a visiting Ivory Coast soccer team and carefully mixtured by the Ivorians, the West African reconciliation is seen as genuine and a major turning point in regional security by Sekou Toure's once skeptical neighbors.

"This has removed the indirect menace that was posed for our region through Guinea," Auguste Denise, acting head of state of the Ivory Coast, said in an interview here last week with Katharine Graham, publisher of The Washington Post. "Our friend Sekou Toure was disappointed with the Communists, and has decided to bring Guinea out of isolation."

This view was echoed in separate interview by President William Tolbert of Liberia and Senegalese Prime Minister Abdou Diouf, in their capitals.

Moreover, the Ivory Coast, Senegal and Liberia served as major staging posts for the emergency Western rescue effort mounted into Zaire's Shaba Province this month without drawing criticism from Guinea or other African states.

In stark contrast to the anti-Western uproar created in Africa by the 1964 airlift of whites from Stanleyville, now Kisangani, there was general acquiesence across the continent this time as the United States, France and Belgium obtained immediate and unqualified logistical support from the three West Africa countries for the Shaba missions.

Diouf of Senegal was awakened at 2a.m. on May 19 by an American diplomat, who asked authorization for C141 transports carrying French Foreign Begion jeeps and some drivers to begin landing at Dakar airport. After asking when his planes would arrive and being told "in about 20 minutes," Diouf immediately told his aides to open the airport to the planes "and worry about paperwork later."

"We wanted to give effective help to any effort by the West that would help reestablish the equilibrium in Africa," Diouf said in his office four days after his decision. "We believe deeply in Africa for the Africans, but the military actions of the Soviet Union and Cuba in the continent have upset the equilibrium, and the West has to help restore restore it."

"The actions in Zaire have been an improvement," said Liberia's Tolbert in a comment that typified the three leaders' individual concerns that the Carter administration has not been doing enough to oppose the Soviets in Africa. "We can't give material support to Zaire because of our limitations, but we will do everything we can politically and morally to help Zaire."

In contrast to the failure of the new cries of alarm from Washington to stem Soviet penetration elsewhere in Africa, the gains made by the West in this region have come through quiet diplomacy. Some of those gains have come through growing aid programs that have helped open up radical or neutral countries hit hard by the four-year drought that ravaged the life-supporting Sahel fringe of the Sahara Desert.

In two years, the U.S. AID mission in Mail has increased from one person to 25, with 40 more staff members expected this year.

Although the Soviet Union contiues to be Mali's only source of military supplies and has about 150 military advisers in the country, West Germany has opened a small military mission in Bamako with a view toward establishing a much larger Western presence.

Western diplomats were encouraged by the results of a Feb. 28 "preemptive coup" by the country's military rulers against a more radical group within the government that wanted to put off promised elections and a possible return to civilian rule.

Overall, an estimated total of $1 billion in development aid is to be channeled this year to eight countries that make up the Club of the Sahel. The United States will contribute $67 million of that amount.

Although no authoritative account is yet available of how Sekou Toure reached his decision to change course in Guinea, the country's continuing economic difficulties and evident hopes of getting some financial help from the West appear to have played an important role.

Sekou Toure has quarreled bitterly with France and with presidents Leopold Senegal and Felix Houphouet-Boigny of Ivory Coast since 1958, when Sekou Toure rejected Charles de Gaule's offer of continued cooperation and decided to go it alone with the help of Soviet bloc countries.

Over the past two decades, the once flourishing economy of Guinea, which is rich in bauxite deposits and agriculture export potential, has limped feebly along, under less than espert management. Moreover, frequent coup plots aimed at Sekou Toure and an abortive invasion of Conakry in 1970 by Portuguese soldiers and African mercenaries created an atmosphere of terror and a large prison population inside the country.

After the 1970 invasion attempt, Sekou Toure plunged Guinea into almost total isolation, accusing Senghor and Houphouet-Boigny of plotting against him and demanding that they force hundreds of thousands of refugees who had fled Guinea to return before he would discuss normalizing relations. The local economy was teetering on the brink of collapse last year when the women who run Conakry's markets took to the streets in an unprecedented, and for Sekou Toure, alarming protest.

It was against this background that Sekou Toure set the West African diplomatic circuit buzzing last December by suddenly rising during a soccer match in Conakry and bowing toward the visiting Ivory Coast team who, he reminded the crowd, "are our brothers."

Like Richard Nixon following up the Chinese signals sent through Ping-Pong diplomacy, Houphouet-Boigny and Tolbert probed to see if Sekou Toure was interested in burying the hatchet. Senghor was more cautious, recalling that the Guinean leader had sent such signals before and then backed out of any reconciliation.

But when Tolbert proposed a summit of the three French-Speaking leaders in Monrovia in mid-March, Sekou Toure agreed in advance to a moderate final communique and did not press his demands on the exiles. A reconciliation was announced at the summit and Guinea is exchanging ambassadors with the Ivory Coast and Senegal. Sekou Toure has also begun to visit his more conservative regional neighbors, including King Hassan 11 of Morocco.

"Our president is encouraging Sekou Toure to resume a good relationship with France," said the Ivory Coast's Denise, who was in charge of the government last week while Housphouet-Boigny was in Paris.

A Western diplomat adds: "Sekou Toure saw he wasn't going to get the help he needs from France as long as he was at daggers drawn with his neighbors."

For Tolbert, who is a Baptist preacher as well as president of Liberia, "The fullness of time has come, and the problem was ready to be solved."