JOHANNESBURG, JULY 9 -- Allan Boesak, a leading South African anti-apartheid crusader, church reformer and president of the World Alliance of Reformed Churches, has resigned from all leadership positions following his admission of involvement in an extramarital affair with a prominent white Afrikaner television producer.

The news, featured prominently in the front pages of today's newspapers, came after Boesak confessed Sunday from the pulpit of his own small Dutch Reform church in Bellville South, a mixed-race community outside Cape Town.

"This is one of the darkest days of my life," Boesak said, according to local newspaper reports. He asked his stunned parishioners for their forgiveness and understanding for the breakup of his 21-year-old marriage and an affair about which he said there was "nothing immoral."

Boesak told his congregation that he was aware of "the high price" he would have to pay for his behavior and that he was stepping down immediately from his ministry of the church. He also submitted his resignation as "moderator" of the Dutch Reformed Mission Church and told his superiors he planned to give up his position as president of the Geneva-based World Alliance of Reformed Churches.

After a five-minute address, Boesak broke down and wept as he left the church embracing many of his longtime friends and parishioners as he went, in a highly emotional scene, according to local press accounts.

Boesak, 44, who is classified as Colored, meaning of mixed racial background, is one of the South Africa's best-known anti-apartheid figures. He was a founder of the United Democratic Front, the umbrella anti-apartheid organization that led a government opposition movement during the 1984-86 township uprisings.

Together with Anglican Archbishop Desmond Tutu, the 1984 Nobel Peace Prize winner, and the Rev. Frank Chikane, general secretary of the South African Council of Churches, Boesak campaigned throughout the world for tough sanctions to press the government into ending apartheid.

During the late 1980s, the three church leaders became the collective voice of 30 million black South Africans at a time when the government had jailed anti-apartheid leaders and banned or outlawed their organizations.

Boesak gained international recognition in 1982 when he persuaded the 70 million-member World Alliance of Reformed Churches to expel the all-white Dutch Reformed Church of South Africa because of its religious support and justfication of apartheid.

Boesak also moved the World Alliance to issue a formal judgment declaring that apartheid "a sin" and that the Dutch Reform Church's theological justification of it was "a travesty of the gospel . . . and a theological heresy."

Boesak led his Colored congregation in a break with the Dutch Reform Church and provoked a major theological debate over apartheid. The Dutch Reform Church admitted that apartheid was "a sin" but ultimately refused to make a full "confession," as Boesak and his supporters were demanding.

Boesak's reputation as a courageous leader within the church got him elected president of the World Alliance when he was 36.

Boesak told an astounded audience on Sunday that his marriage to his wife Dorothy had been failing "for some time now," a widespread suspicion ever since a 1985 affair with a white church worker, Di Scott, which led to his temporary suspension from the church. That affair had been exposed by security police surveillance.

Boesak's latest revelation is far more dramatic, however. His resignation announcement followed reports published Saturday and Sunday in the South African press about his six-month relationship with Elna Botha, niece of the former minister of home affairs, Stoffel Botha. She is a well-known television producer.

Botha works for the state-run South African Broadcasting Corp. and her husband, Colin Fluxman, is a radio personality and television news anchorman on the "Good Morning South Africa" program -- on which he haltingly read the news of the scandal.

Boesak's wife told the Johannesburg Sunday Times that she had recently confronted Boesak with reports she had received about his affair with Botha and that he had admitted it.

"This time he has gone too far. I can't go through this again. Our marriage is over," she told the newspaper.

Boesak and Botha were recognized by a chambermaid at a seafront hotel last week in Cape Town who realized they were sharing a room and said she felt "a man in his position should not act like that."

The chambermaid then tipped off a Cape Town Afrikaans-language newspaper, Die Buerger, which sent a reporter to confront Boesak and Botha at the hotel. The chambermaid also phoned Boesak's wife with the news, according to local press reports.