The Reagan administration's policy toward white-ruled South Africa is an "unmitigated disaster" for the country's black majority, a church official said this week.

"We find it galling that the leader of the so-called free world should be hobnobbing so closely with our oppressors," said Bishop Desmond Tutu, general secretary of the South African Council of Churches.

Blacks will remember that Washington "collaborated with and supported a regime perpetrating the most vicious system since Nazism and communism," he said. "Perhaps the United States wants blacks to know that ultimately they are expendable," Tutu said in his annual report delivered to the SACC's national conference.

The United States had imposed sanctions against Cuba and "was ready to risk the wrath of its Western allies" over the embargo on the Soviet gas pipeline, Tutu said.

"But when it came to South Africa, the Reagan administration was prepared only to consider 'constructive engagement' when South Africa should have been written off as a dismal failure."

Constructive engagement--the Reagan administration's policy of improving relations with South Africa--"has not achieved independence for South West Africa-Namibia, nor has it stopped bannings or forced removals," said Tutu.

Banning orders restrict freedom of speech, movement and association. Tutu's reference to "forced removals" concerned mandatory resettlement of blacks in rural areas.

The United States will "rehabilitate" itself in the eyes of blacks only after it has "disengaged from South Africa, spoken up for human rights and taken action to back up its leaders' fine words," Tutu said.

Turning to the South African government's Commission of Inquiry, which has been scrutinizing the South African council for nearly a year, Tutu accused the government of trying to cripple his organization for "disgracefully unworthy political motives."