Nine African nations, in an implicit criticism of the Reagan administration, today appealed to Western nations not to treat the continent as part of the East-West struggle.

In the message to the Ottawa summit of Western industrial nations, the leaders of the Southern African Development Coordination Conference, said: "We are alarmed that the crumbling of detente has increased East-West tension and the resulting conflicts are spilling over into our region."

The leaders, seeking to reduce their economic dependence on South Africa, expressed concern at President Reagan's courting of the white minority government in Pretoria because of its anti-Soviet stance, conference sources said. The African heads of government hoped that European influence could bring about a change in the U.S. attitude.

The message, sent to Canadian Prime Minister Pierre Trudeau at the conclusion of a one-day summit, here also criticized "the faltering of the West's commitments to end South Africa's illegal occupation" of Namibia.

The nine nations, which stretch from the Atlantic to the Indian Ocean and reach more than 2,000 miles north of Cape Town into the heart of black Africa, contain large supplies of minerals vital to the West, including copper, chrome and cobalt.

Opening the meeting, Prime Minister Robert Mugabe criticized Western "monetarist ideologies. With some exceptions they seem mesmerized by economic theories which place little or no value on the human person," the Zimbabwean leader said.

"International society is based on an unjust economic structure," he said, adding that the refusal of the West to transfer resources to the Third World "is morally indefensible and extremely shortsighted."

Mugabe condemned South Africa's spartheid policies of racial separation and reiterated his frequent criticism of efforts to alter a United Nations resolution designed to bring South African-controlled Namibia to independence. He did not mention the United States by name, but the Reagan administration is seeking to change the plan to make it acceptable to South Africa.

His remarks, however, were much more moderate than the criticism at last month's Organization of African Unity summit, which spoke of "an unholy alliance" between the United States and South Africa.

There was no mention of South Africa or Namibia in a joint communique, which approved the establishment of a small permanent secretariat.

The organization, established last year in the African euphoria over Zimbabwe's independence, comprises seven Western-oriented former British possessions -- Tanzania, Zambia, Zimbabwe, Malawi, Botswana, Swaziland and Lesotho -- and two former Portuguese colonies, Angola and Mozambique, which are closely associated with the Soviet Union. Zaire sought to join but was turned down because of a territorial dispute with Zambia.

Most members route their international trade through South Africa despite their hostility to its racist policies. Lesotho, which is surrounded by South Africa, the Swaziland, uses South African currency. About 80 percent of Zimbabwe's trade moves on the southern route and last year Zambia avoided famine only by buying emergency supplies of corn from Pretoria.