The Congressional Black Caucus yesterday denounced the U.S. veto of a United Nations Security Council resolution condemning South Africa as "a dastardly act" that marked "an all-time low in the morality of the Reagan administration's foreign policy."

Caucus chairman Del. Walter E. Fauntroy (D-D.C.) said the vote on Monday night was a bitter blow that damaged American interests in Africa and constituted a dangerous break with allies around the world.

The Security Council voted 13 to 1 for a strongly worded resolution condemning South Africa for its raid last week into Angola, with the United States casting the only vote against. American officials said they were unhappy that the resolution singled out South Africa and did not put the incident in context.

Fauntroy said the American vote epitomized the administration's support for fascist regimes around the world and was not "neutral" as the administration claimed.

"We believe the veto was a tragic break with our allies in the U.N., that it seriously endangers our relations and credibility with the nations of Africa on whom we depend for large amounts of natural resources, and that this action was both highly immoral and clearly not in the best interests of the United States," the caucus said.

Fauntroy said the American veto would encourage South Africa to continue its "reckless military action" in the region. U.S. abandonment of the terms for a Namibian settlement favored by the Carter administration, he said, showed a recalcitrant attitude that would help the South Africans to continue to resist reforms in the apartheid system.