Several of this country's largest corporations, whose executives have been among Ronald Reagan's most enthusiastic supporters, have become apprehensive about key elements of the administration's Africa policies.

Fearing that potentially profitable operations in what is seen as a rapidly expanding market could be jeopardized, these companies have quietly passed the work in Washington that vital business interests could be adversely affected by the government's handling of such sensitive issues as independence for Namibia, white rule in South Africa, Cuban troops in Angola, and bilateral relations with such economically important nations as Zimbabwe and Nigeria.

The corporate concerns began to solidify as early as January, when business executives at an African-American conference in Freetown, Sierra Leone, talked informally about the implications of Reagan administration policies. Since then, apprehension has been conveyed to the administration in ways ranging from a private letter from Chase Manhatten Corp. Chairman David Rockefeller, before his retirement, to high-level meetings at the White House and on Capitol Hill.

Angola, which was the subject of Rockefeller's letter, is perhaps the clearest example of how the Reagan administration's geopolitical strategies have come into direct conflict with the goals of corporations whose leadership strongly supported the Reagan candidacy. Despite the lack of diplomatic relations between the United States and Angola, visits by American representatives to Luanda have become routine, and Angolan government officials are regularly in New York corporate offices.

Angola's economy "could be poised for a takeoff," says the current issue of Chase Manhattan's newsletter for coporate customers and correspondent banks. Along with the obvious assets of oil and diamonds, "the liberal investment code and sound economic management policies of the government are attracting increasing numbers of foreign firms," Chase economists report.

Many companies doing business in Africa are worried that U.S. attempts to destabilize the Angolan government of Jose Eduardo dos Santos -- by assisting the dissident movement UNITA, led by Jonas Savimbi -- may backfire. At stake, they feel, are not only current and potential interests, mostly oil-related, but also interests in nations that already have warned of reprisals against U.S. intervention in the affairs of a sovereign African state.

"The U.S. attitude toward one problem affects the African perception of the positions the U.S. might take in other areas of Africa," Gulf Oil's Melvin Hill told Congress at hearings in April, arguing against repeal of the Clark amendment, which bans clandestine aid to UNITA. Gulf, which is pumping 100,000 barrels a day from the northern Angolan enclave of Cabinda, advocated normal relations between the United States and Angola.

In addition to the congressional testimony, the president of Gulf Oil, James Lee, and Hill, president of Gulf Oil Exploration and Production Co., met with Vice President Bush on April 1 to discuss the administration's policies.

Another illustration of the diverging perspective of the administration and members of the corporate community came last month. During the same two days that three senior State Department officials were in Cape Town talking with South African government leaders, a dozen business and foundation executives were holding unprecedented meetings in New York with Oliver Tambo, president of South Africa's oldest and best known black-led political organization, the outlawed African National Congress.

The ANC's stepped-up guerrilla campaign has been responsible in the past two years for attacks on strategic government installations, including one that caused more than $7 million in damage to a secret, heavily guarded coal gasification plant.

According to the executives, more and more corporations recognize that political change in South Africa is inevitable, and that the issue of change is a sensitive one in the rest of Africa and the world. Companies say they are taking seriously the recommendations of the Study Commission on U.S. Policy Toward South Africa, a panel of business, labor, and academic leaders whose $2 million, two-year study for the Rockefeller Foundation produced a report in May entitled "South Africa: Time Running Out."

Rejecting disinvestment and trade embargoes, the commission, nevertheless, called on U.S. firms in South Africa to "commit themselves to a policy of nonexpansion" and to devote "a generous portion of corporate resources to improve the lives of black South Africans."

"We're looking at this very closely," said a vice president at Citibank, the nation's largest financial institution and the only American bank with branch operations in South Africa, although many others do business there. Citibank also operates in 13 other African countries and plans to open a Zimbabwean branch in September.

Its involvment in South Africa, including participation in a $250 million loan last year to the government for black schools and hospitals that prompted several church organizations to cut business ties with the bank, has not created problems with African governments, bank officials maintain. And they believe the controversial loan follows at least the spirit of the guidelines proposed by the Study Commission for acceptable exceptions to the ban on increased investment or lending.

The turnout for Tambo is regarded as a signal that the companies involved want to be prepared for whatever comes in South Africa. Although invitations to the June 12 dinner went out less than 48 hours in advance, they attracted three of the top 10 American investors in South Africa -- Ford, General Motors and General Electric -- along with three of the largest U.S. banks -- Citibank, Bank of America and Manufacturers Hanover Trust.

Foundation presidents Franklin Thomas of Ford, who chaired the Rockefeller Commission, and Alan Pifer of Carnegie, a commission member, met with Tambo at a morning coffee attended by trustees of the African American Institute, which also gave the dinner. Financed by corporations, foundations, and U.S. government contracts, AAI seeks to promote understanding between Africa and the United States.

The lobbying efforts and the ANC contacts are signs of a developing corporate consensus about what kinds of Africa policies best serve American economic interests, according to executives interviewed here and in other cities in recent weeks.

"Clearly evident today in the business community is a deeper interest and knowledge about Africa than ever before," says J. Wayne Fredericks, Ford Motor Co.'s executive director of international government affairs. Fredericks, who was in Freetown and whose own direct experience in Africa predates his tenure as deputy assistant secretary of state for Africa in the Kennedy administration, believes "business has moved a long way toward a comprehension of Africa that goes beyond labels and stereotypes. The result has been corporate actions that would have been unthinkable just three years ago."

From the Freetown discussions and subsequent conversations and meetings, general agreement emerged on five policy areas, these executives say. In addition to the concerns about South Africa and Angola, business leaders believe the United States must continue to accelerate efforts aimed at an internationally acceptable independence plan for Namibia, and stress the need for improved relations with Zimbabwe and Nigeria.

Namibia is at the top of the Africa leadership's agenda, and any perception of U.S. complicity in South African footdragging is seen as creating a potential backlash in countries where American companies are competing with Europeans and Japanese for contracts.

The backlash may have already begun, said Donald Easum, president of the African American Institute. Easum pointed to resolutions adopted three weeks ago by the Organization of African Unity that singled out the United States for criticism in its Namibia declaration and said the Reagan policies amounted to an "emerging unholy alliance between Pretoria and Washington.

"The American companies that are interested or involved already in doing business with Africa surely have to be concerned by this kind of expression of African view," Easum argues, "because if they want to do business in Nigeria or Kenya, the Ivory Coast or in Cameroon, or if they are already there, they surely must be alarmed by the fact that the leaders of those countries joined in this condemnation of U.S. policy."

In Zimbabwe, corporations favor expanded U.S. relations and what one executive calls "efficient, accelerated economic assistance."

"American policy toward Zimbabwe should follow concrete national interests rather than ideological labels," the Zimbabwe trade and investment group of the U.S. Chamber of Commerce said in a February statement. "While Zimbabwe's leaders espouse certain Marxist ideas, they have purused policies of friendship with the United States." The group's members include executives from Union Carbide, Westinghouse, Manufacturers Hanover Trust, Ford, Bankers Trust, and H.J. Heinz.

The oldest and largest U.S. investor in the area, Union Carbide, whose pre-indenpendence support for sanctions-violating mineral imports made it the target of boycotts and protests, has quickly settled into a comfortable relationship with former guerrilla leader Robert Mugabe's government. Company Chairman William S. Sneath, who recently attended the dedication of new ferrochrome furnaces at Que Que, commended "Zimbabwe's growing political stability and its democratic society. Union Carbide supports your goals."