Vice President George Bush emphasized for Africa today the Reagan administration's newly public commitment to a Cuban pullout from Angola as "the key" to a negotiated independence for the South African-controlled territory of Namibia.

Bush's speech, near the end of a seven-nation swing through Africa, was billed as a key address on U.S.-African relations -- concentrating on the continent's economic problems. But the first half of the speech was devoted to the Namibian issue.

Bush has used his trip through African countries, which have been suspicious of the U.S. bargaining tactics in the complex Namibian negotiations, to make explicit the American determination to link Cuban withdrawal from Angola to a Namibian settlement. Previously the Reagan administration had made this demand only in private communications.

The setting for the speech strengthened the U.S. message. Bush was speaking at a dinner the day of his arrival in Kenya, an East African country that has strong ties with the United States and is perceived as a staunch ally of the Reagan administration.

Addressing guests who included Kenyan Vice President Mwai Kibaki, Bush said, "The withdrawal of Cuban forces from Angola in a parallel framework with South Africa's departure from Namibia is the key to the settlement we all desire. . . . My government is not ashamed to state the U.S. interest in seeing an end to the presence of Cuban forces in Angola. Their introduction seven years ago tore the fabric of reciprocal restraint between the United States and the Soviet Union in the developing world. Such restraint is vital if African regional security and the global balance are to be maintained."

In a reference to the U.S. approval of the recent $1.1 billion International Monetary Fund loan to South Africa, Bush said, "The United States seeks constructive relations with all the states of southern Africa. We are building bridges of communication to each nation in the region, including South Africa."

The IMF loan was unsuccessfully opposed by black African states in the United Nations General Assembly. Part of the reason for their opposition is that the loan is viewed as a subsidy for South Africa's stepped-up military operations in Namibia and frequent raids against SWAPO camps in Angola. SWAPO -- for South-West Africa People's Organization -- is the political group expected to win elections in Namibia. Its Angola-based guerrilla arm has been fighting for several years to end South Africa's control over the disputed territory.

Bush will be treading a delicate line during his Kenyan visit. Severe economic difficulties have drawn the Kenyans into negotiations with the IMF as well as with other donors for more aid. The IMF loan to South Africa is a sore point with the Kenyans.

Kenyan officials have been in Washington this week for discussions on the resumption of a $162.5 million standby credit that has been suspended since early August. IMF officials are expected in Kenya early next month to discuss the issue.

The present standby credit agreement was informally suspended, because of Kenyan government overspending, just one day after an abortive attempt by Air Force junior officers to overthrow the government. Although the timing was coincidental, it served further to shake confidence in this once politically and economically secure country.

Against a background of paralyzed industry and reduced foreign exchange reserves, the Kenyans have also appealed to 12 donor countries to provide about $330 million in budget support to help offset a serious balance-of-payments deficit. The United States was asked to come forward with the largest amount -- $100 million -- even though Britain and West Germany both have a record of being more generous givers. The donors met in London on Tuesday to discuss the appeal, and reportedly agreed to increase aid 20 to 30 percent.

The United States already had offered $15.1 million in budget support last month, the first donor to do so. But observers do not expect that any substantial additional cash will be coming from donor countries that are themselves experiencing budgetary difficulties.

Bush pointed out that the United States contributes more than $1.4 billion a year to Africa either directly or through multilateral agencies such as the United Nations and the World Bank. Of this total, $800 million is lent directly to 46 African states each year. Bush made no promise of any additional aid, referring instead to the role of the private sector in development.

"The recent enactment of export trading legislation supported by President Reagan will make it possible for small and medium U.S. firms to pool expenses, and thereby play a more active economic role in Africa," he said.

Kenya allows the United States to use its airports and Indian Ocean port for the U.S. Rapid Deployment Force. The United States this year provided Kenya just over $100 million in aid. About a third of this was for military equipment purchases and training.