Bedrock of white unity in S. Africa cracking

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.

The biggest split in the Afrikaner community occurred last year, when disgruntled members of the National Party, led by Andries Treurnicht, formed the Conservative Party. The resounding victory of Dr. Treurnicht and the near defeat of a senior Nationalist in by-elections earlier this year has given new momentum to the Conservative Party.

The Broederbond is not as powerful as it once was, no longer having the degree of influence it once did on major government policy decisions. However, University of Cape Town political scientist Dr. Hermann Giliomee says the Broederbond remains important.

''It provides ideological cement, it's a cohesive force,'' for the Afrikaner community, he says.

The organization's influence is said by experts to be greatest now in the field where it helps to shape government policy.

The Nationalist government appears to have won stronger support from the leadership of the Broederbond with the appointment of Prof. Jan de Lange as new chairman.

Dr. de Lange was chairman of a committee that two years ago produced a controversial report on education in South Africa. Some of its suggested reforms , including more autonomy for schools and universities on enrollment, were rebuffed by the government. Generally the reform initiative that was assumed to be behind the government's appointment of the de Lange committee seems to have evaporated.

However, some analysts feel de Lange's rise to chairman of the Broederbond suggests at least that the government was not unhappy with the committee's recommendations. De Lange is considered a supporter of the more pragmatic wing of the National Party, and thus an ally of the prime minister.

The appointment of de Lange as new head of the Broederbond is not expected to set well with many of its more conservative Afrikaner members. Some analysts expect divisions in the organization that have been simmering since the formation of the Conservative Party last year to now become more open, with some Conservative supporters possibly leaving the group and forming a rival organization.