CAPE TOWN, SOUTH AFRICA, OCT. 1 -- The first signs of a split developing between the African National Congress and the South African Communist Party, longtime allies in the anti-apartheid struggle, surfaced here this weekend when two well-known Communists withdrew from the first regional ANC elections.

In a successful bid for leadership of the ANC's Regional Executive Committee, veteran ANC member Christmas Tinto spoke strongly against the deeply entrenched practice of holding leadership in both parties, prompting the withdrawal of his two Communist rivals for the position.

The issue of extensive overlapping leaderships between the ANC and Communist Party has been defended by both parties as a legacy of three decades of common clandestine activity against the white-minority government.

Since both parties were legalized last February, they have been reluctant to confront the issue directly, but Tinto, a founder of the umbrella anti-apartheid United Democratic Front, forced the issue into the open.

Tinto declared publicly on the eve of the ANC's first Western Cape regional conference since February that he believed the principle of "dual leadership" was wrong. "We believe in the {ANC-Communist Party} alliance. But this means separate parties," Tinto told the weekly Vrye Weekblad. "How can a person be a leader of two parties at the same time?"

Tinto, who is black, is known to be vehemently anti-Communist and has not hidden his disquiet at the emergence of many Communists, often Coloreds, as persons of mixed race are called, in the ANC and United Democratic Front Cape leadership.

His blunt warning to the Communist Party was the first publicly voiced by any leader of the ANC. Nelson Mandela, the ANC's leader, has so far accepted what amounts to a system of interlocking directorates between the ANC and Communist Party leaderships.

In late July, the highly secretive Communist Party announced a 22-person interim leadership group, 12 of them Central Committee members. Of the 22 names disclosed, eight were members of the ANC's 35-member National Executive Committee.

Such a system of overlapping leaderships -- and memberships -- is believed to be unique in the annals of Communist Party relations with other political organizations around the world. Analysts have been wondering how long the system can function now that both parties are scrambling to organize separately, appealing often to the same constituency.

Tinto's warning against dual leadership apparently struck home, both with ANC delegates and Communist Party officials here. He won election as president of the ANC's Regional Executive Committee and his two Communist rivals, Reg September and Cheryl Carolus, withdrew from the contest.

September, a Colored, is a member of both the Communist Party Central Committee and the ANC National Executive Committee, serving as the most senior ANC official in charge of organizing in the Western Cape.

Carolus, also a Colored, is a young firebrand street speaker and rising star in the ANC, the Communist Party and the United Democratic Front, a coalition of hundreds of anti-apartheid organizations. She was selected over more senior ANC officials to participate last May in the first round of talks about the nation's political future with President Frederik W. de Klerk.

But since her Communist Party ties became known in late July, Carolus has run into criticism in the black townships, not only for her Communist ties but also for her accumulation of top jobs in four different organizations, according to local sources.

Carolus told reporters, without referring to Tinto's warning, that she had decided to concentrate on Communist Party organizing and would not stand for any ANC leadership position. September was made an ex-officio member of the 14-person regional ANC executive.