United Nations Secretary General Kurt Waldheim today condemned South Africa before an African assembly for causing "bloodshed and destruction" in Angola.

Waldheim spoke at the opening meeting of the Organization of African Unity summit here. The conference began amid tensions among member nations and under conditions of unusually strict security.

The U.N. leader, in addition to expressing his profound regrets" about the violence in Angola, noted increasing repression within South Africa and said: "The spectacle of school children having to take the streets to protest the injustice of South Africa's policies in education is another grave indictment if its discriminatory system."

The OAU was meeting, Waldheim said, "at a time of marked deterioration in international relations. Mistrust prevails to a degree which exceeds all considerations of prudence or perceptions of self-interest."

Senegalese President Leopold Senghor, in his opening address as acting OAU chairman, seemed to confirm Waldheim's perceptions as he recited a list of the OAU's failure to get cooperation on projects ranging from african human rights charter to a peacekeeping force for civil war-torn Chad.

Senghor said the OAU will probably have to ask the United Nations to supply peacekeeping troops for Chad because ideological differences and lack of money have frustrated OAU attempts to organize such a force. Those attempts began with the founding of the organization in 1963.

Senghor reported that meetings within the last year to draft an all-African human rights charter had failed "because of serious differences" among the nations on the substance of human rights.

The charter was promoted last year as a way to lessen the domestic strife that has slowed economic progress in many African countries.

At least one major conflict at today's meeting was defused when the Liberian delegation announced that the country's new head of state, Master Sgt. Samuel Doe, would not attend.

The late OAU chairman, Liberian president William R. Tolbert, was assassinated in April in a coup led by Doe and other military officers. In handing over the gavel to Sierra Leone President Saika Stevens, Senghor harshly criticized the assassination.

He said he had told Doe in a May meeting that while the coup was an internal matter, the murder of Tolbert "was a serious act in violation of the OAU charter" and deserved condemnation.

When Stevens called for a moment of silence in memory of the late leader, all of the delegates stood except the Liberians.

Security surrounding the 50-nation conference was tight today. Soldiers carrying submachine guns were in evidence everywhere and a local paper reported that vagrants, students, a university professor and other potential troublemakers were being held in detention.

The summit has become controversial in Sierra Leone because the government is spending between one-half to two-thirds of the country's annual budget on it -- an expenditure of about $200 million.