The sacred shrine of this country's ruling white Afrikaner minority - the Voortrekker Monument - is a solid, seemingly unassailable piece of architecture. The Afrikaner community is proving less so. The pressures of rising black nationalism continue to produce cracks and divisions within this once united group, who are descendants of South Africa's early Dutch settlers.
The latest tremor is the resignation of the chairman of the semisecret Afrikaner Broederbond (Band of Brothers), a political-cultural organization formed in 1918 to promote the interests of the Afrikaners. The resignation of Prof. Carel Boshoff, a son-in-law of apartheid architect Dr. Hendrik Verwoerd, is but a surface sign of a split within the members of the organization, say knowledgeable analysts.
A central theme of the Broederbond through the years has been the necessity of unity among Afrikaners. But that unity is fast being lost as the political arm of the Afrikaner community - the National Party - tries to adapt the ideology that Afrikaners have been taught is the key to their survival in a land where they are outnumbered by blacks.
That ideology is one of racial exclusiveness, calling for strict separation of the races in all spheres.
The present Nationalist government of Prime Minister Pieter W. Botha has set off alarm bells in the Afrikaner community with its plan to bring Coloreds (persons of mixed-race descent) and Indians into the presently all-white Parliament, albeit in separate chambers.
While many Afrikaners see the plan as going too far toward integration, critics to the left see it as nothing more than an attempt by the ruling whites to coopt some nonwhites into opposition to the black majority.
Dr. Boshoff is one of those influential Afrikaners who feels that once the ideology of strict racial separation is fudged, the threat to Afrikaner survival will rise, with chaotic and probably violent results.
Boshoff is also chairman of the South African Bureau of Racial Affairs (SABRA), a research organization that officially rejected Botha's proposed constitutional changes as leading to ''total integration.'' The executive council of the Broederbond said Boshoff's resignation was necessary because he was also head of an organization that openly opposed the government's constitutional plan.