"At no time in my lifetime has the opinion of blacks [in South Africa] of the United States been so low as now," the Rev. Allan Boesak, a South African clergyman and president of the World Alliance of Reformed Churches, declared here this week.

Blacks in South Africa "perceive the United States [government] to be on the side of the [white] minority rule" in the present situation in South Africa. "We perceive the United States to be racist," said Boesak, who was in the Washington area to speak to the National Presbyterian Peacemaking Conference, held in Arlington.

"We perceive the United States administration to be concerned only with the white power structure."

Boesak, 39, also is scheduled to preach tomorrow at the New York Avenue Presbyterian Church, a longstanding commitment that will keep him from attending the installation ceremonies back home of Bishop Desmond Tutu as Anglican Bishop of Johannesburg.

Last month Boesak and Tutu together hosted the visit of Sen. Edward M. Kennedy (D-Mass.) to their homeland. Boesak had glowing praise for that visit, despite the stormy protests it generated in some quarters.

"The visit was very successful," Boesak said in an interview. "Sen. Kennedy came and highlighted the issues" of apartheid and discrimination against blacks. The visit was important "not because no one knew [the problems] were there," but because Kennedy's visit "highlighted the gap" that exists between South Africa's white minority government and the disenfranchised black majority.

It was also important that Kennedy "came as a powerful politician from the United States who came as a guest of black people . . . who sawSouth Africa through the eyes not of the government, but of the opposition."

Kennedy, he continued, "came and was willing to listen. I remember, talking with people after he had left, ordinary people, who were absolutely amazed that he was willing to sit and listen, that he was willing to take a serious interest in what they had said."

Boesak criticized the anti-American demonstrations by the black-consciousness Azapo (Azanian People's Organization) that dogged Kennedy's visit and prevented him from speaking to a large crowd in Soweto, an all black suburb of Johannesburg. "Azapo has lost so much credibility in the black community because of this," Boesak said. "Azapo has effectively isolated itself now."

Boesak had high praise for the current apartheid protests in front of South African installations in Washington and other major U.S. cities. "As far as [South African] black people are concerned, it's one of the most important things that could have happened in the United States," he said, adding, "It's particularly important that black Americans are taking the lead" in such demonstrations.

South Africa's controlled press has screened out most information on the protests here, he said, but word is still getting through. "If only there was a way that blacks in South Africa could convey their excitement" over the protests here, he said.

Boesak, who has done religious studies in the Netherlands and at Union Theological Seminary in New York as well as South Africa, said that the decision by the World Alliance of Reformed Churches two years ago to define apartheid as "heresy" was an important tactical move.

"It made very, very clear at the worldwide level how unacceptable apartheid is," he said.

In addition, he said, the action "helped to undermine the moral justification that is so important in the South African context" where the white Dutch Reformed church "really liked to think that apartheid could be justified by the Bible." The South African Reformed churches were subsequently expelled from the World Alliance for refusing to renounce the "heresy" of apartheid.

Boesak said that those churches, to which most South Africans of Dutch ancestry belong, have "officially" shown no signs of moving from their support of the government's racial policies. "But within the church there are signs that people are very concerned . . . "

He said that Roman Catholics are playing "an increasingly important role" in the battle against apartheid "under the leadership of Archbishop [Denis E.] Hurley," president of the South African Bishops Conference.

Hurley faces trial in South Africa later this month for criticizing that government's racial policies.

Boesak himself was threatened with arrest last year after an Australian newspaper reported he had accused South African police of brutality and "atrocities."

In his address here, he expressed thanks to American Presbyterians for their letter-writing campaign to intercede with South African authorities in his behalf.