President Kenneth Kaunda has sharply criticized Reagan administration policies in black Africa and said former president Jimmy Carter was more favorably disposed toward the continent.

In an interview last week with Katharine Graham, chairman of the Washington Post Co., Kaunda said U.S. relations with black Africa would deteriorate unless Western negotiations bring about the independence of Namibia, which is controlled by South Africa in defiance of the United Nations.

The United States, he said, was wrong to insist that a Namibian settlement must be linked to withdrawal of 15,000 to 20,000 Cuban troops from Angola. Thousands of South African troops based in Namibia freqently invade Angola looking for guerrillas fighting for independence for Namibia.

"We do not see why there should be any connection between the withdrawal of the Cubans and the independence of Namibia," he said. "America is losing a lot over this issue."

Kaunda, 58, one of the key leaders in the struggle to end colonialism in Africa, said he was "shocked" by President Reagan's description last year of white-minority-ruled South Africa as an "ally" of the United States.

"Where have we gone wrong?" he asked. "Why should Americans choose South Africa as friends? . . . Why should the United States want to alienate itself from 24 million blacks in South Africa, the eventual rulers?"

Kaunda spoke of a coming bloodbath in South Africa in which the death toll could far exceed those in the wars for independence in neighboring Zimbabwe, Mozambique and Angola. All of southern Africa would be swept into the conflict, he predicted.

Maintaining that U.S. relations with black Africa would deteriorate in such a situation, he said, "I am afraid the future for a country that has not seen the need for majority rule in South Africa is not very good in terms of good relations between that country and the majority."

He contrasted Western willingness to impose economic sanctions on Poland because of repression of its people with the refusal of the West to take similar measures against South African oppression of blacks. He implied that the West was acting on a racial basis, acting against suppression of whites but not when blacks suffer discrimination.

"I'm afraid I see a lot of difference" between Reagan and Carter, he said. The president spoke warmly of Carter and recalled that he met with him for seven hours during his visit to Washington in 1978. He has not visited Reagan.

In 1977 he visited then-president Gerald Ford, who saw him for only 45 minutes. "I was shocked," Kaunda said. "It was a very expensive flight for the Zambian taxpayer."

Noting his inability to buy arms in Europe or the United States, he said, "We have you in the West to thank for our turning to the Soviet Union for weapons.