A silent struggle is under way within the Carter administration between its global strategists and its "Africanists" over how the United States should respond to the growing Soviet-Cuban involvement in various conflicts throughout Africa, particularly in the trouble-ridden Horn.

At issue is whether policy toward Africa will be subordinated to the United States' overall relationship with the Soviet Union, as it was under former secretary of state Henry Kissinger, or treated separately with a focus on black Africa.

The two chief protagonists are President Carter's national security adviser, Zbigniew Brzezinski, a specialist in Soviet affairs, and the ambassador to the United Nations, Andrew Young, an Afro-American with a deep personal interest in black Africa.

While neither Carter aide is advertising his particular approach toward U.S. policy in Africa, there can be little doubt to anyone following this continent's affairs that Young and Brzezinski are at odds over how to handle the Soviet-Cuban challenge.

Judging from the almost daily denunciations of Soviet-Cuban activities coming from Washington, it appears as if Brzezinski is gaining the upper hand. In any case, the Horn of Africa and Rhodesia are becoming the testing grounds of these two policy makers' influence at the White House.

For the first 10 months of the Carter administration, Young, backed by Africanists in the State Department and U.N. mission, seemed to be setting the tone of American policy.

Young's main aim was to persuade black Africa that the motivating force in American policy was not longer fear of communism and rivalry with the Soviet Union but a sincere concern for the welfare of the continent and a desire to help it find "African solutions for African problems," limiting big power interference.

The best U.S. response to the Soviet Union and Cuba, Young and his aides argued, was to "play it cool" and count on African nationalism to prevail in the end over any Soviet-Cuban designs in Angola, Ethiopia or elsewhere. They pointed to the ouster of the Soviets first from Egypt and then from Sudan and Somalia as proof of the soundness of this approach.

With the Africanists in command, the United States decided not to get involved in Zaire's war in Shaba Province last March and resisted the temptation to send arms to Somalia after it expelled the Soviets, despite President Carter's personal interest in helping the Somalis. It also helped work out a new Anglo-American plan for settling the Rhodesian dispute in close consultation with the five black "front-line" states.

The Soviet Union and Cuba apparently decided to exploit rather than match this new U.S. restraint, pursuing even more vigorously their involvement in African affairs, most notably in the Horn of Africa but also in southern Africa.

Finally, starting in November, the Carter administration's response to the Soviet-Cuban challenge changed, and the "cool" approach advocated by Young went by the boards. To all appearances, Brzezinski was largely responsible for this shift.

It was Brzezinski who first disclosed to the press in mid-November that Cuba, far from withdrawing its troops from Angola, was increasing the number there. He also began linking Cuban and Soviet activities in Africa to the larger issues of overall U.S. Cuban and U.S. Soviet relations.

He has made it clear to journalists in Washington that the Carter administration is deeply concerned about the developing pattern of massive Soviet-Cuban intervention in Africa.

Brzezinski and his aides linked Soviet-Cuban policy here to such apparently dissimilar problems for the administration as the Panama Canal treaties talks with the Soviets on the Indian Ocean and strategic arms-limitation and the role of the Communist Party in Italy. All involve, in their view, the overall balance of power between the United States and Soviet Union, according to one National Security Council member.

The feeling of the global strategists seems to he that the time has come for Washington to stand up to Moscow and counter its repeated thrusts into the conflicts of this troubled continent.

Brzezinski's attitude toward Africa is strikingly similar to that of former secretary of state Kissinger, who generally ignored the problems of black Africa until he became worried about expanding Soviet-Cuban involvement, first in Angola and then in the black nationalist struggles in Rhodesia and Namibia.

This led him to step up clandestine support through the CIA, for the prowestern factions in the Angolan civil war and to formulate a peace plan for Rhodesia in cooperation with South Africa. Both initiatives failed and led to deep suspicion throughout Africa that the United States was only interested in the continent's affairs because of its superpower rivalry with the Soviet Union.

The depth of African feeling became clear in early 1976 when Kissinger was formally accused by the Organization of African Unity of attempting to export to Africa the "policy of political destabilization" allegedly followed by the United States in Latin America.

It was this deep African suspicion of American motives that Young set out to overcome. This led him to make several controversial statements early last year, such as saying that Cuba was playing a "stabilizing" role in Angola and that the real danger of Africa was not communism but racism.

In the past few months, however, Young has noticeably changed his tune about the Cuban role in Angola and Ethiopia, although he is known to still believe that the "cool" approach to the Soviet-Cuban challenge is the sounder one.

Meanwhile, the global strategists appear to have convinced President Carter that no U.S. presence, or only a low level one in response to the Soviet-Cuban buildup in Ethiopia could be highly "destabilizing" to the overall American position vis-a-via the Soviets.

The ultimate test of the two policymakers' influence has still to come, however, both in the Horn of Africa and in Rhodesia.

If Young has his way, the United States will protest vigorously in words only over the Soviet-Cuban intervention in the Horn while avoiding direct involvement in the Somali-Ethiopan conflct.

If Brzezinski prevails, Washington will probably soon switch its position and at the least begin encouraging its Arab allies Saudi Arabia, Egypt and Sudan - and Iran to come to the rescue of Somali President Mohammed Siad Barre. At the other extreme Washington may begin sending arms directly to Somalia, as is already being hinted by Secretary of State Cyrus Vance.

In Rhodesia, the moment of choice is fast approaching. If Prime Minister Ian Smith concludes a separate agreement with the three moderate black leaders based inside that country, the power struggle among African nationalist factions is certain to escalate.

The United States will have to decide whether to back Smith's internal settlement plan or stick with the Anglo-American peace plan that gives the externally based guerrilla alliance, the Patritoic Front, a central role.

The Soviets and Cubans have already chosen. They are arming and training the Front's guerrillas. So far, Washington and London have been courting the external and internal black nationalist leaders simultaneously while providing arms to none.

If Young's advice is taken, the United States will stay with the Anglo-American plan and the Patriotic Front and compete with the Soviets and Cubans for its favor. At the same time, Washington will give no covert or overt backing to the Smith settlement scheme, even if London eventually does.

If the Brezezinski out look prevails, the Carter administration may well cast the American choice in the perspective of the U.S. Soviet conflict and opt to support Smith's internal settlement with the more moderate black nationalists.