Johannesburg — A couple of hours before sunset, the sky is already growing dim from the smoke of coal-burning stoves in the black township of Mamelodi, just outside South Africa's capital city of Pretoria.
Blacks are streaming home from jobs in the ''white'' areas and past the stone and mortar church where Nico Smith, a white, has become the new minister.
''It's exciting to be back in the black community,'' he says. ''But it is also traumatic to discover after an absence of 20 years that physical conditions did not change. What changed was that blacks' bitterness grew enormously.''
Mr. Smith blames, in part, his own Dutch Reformed (Nederduitse Gereformeerde, or NG) Church for providing a biblical justification for South Africa's policies of strict racial segregation, which he feels have led to such bitterness among blacks.
The Mamelodi Church Council asked Mr. Smith to be minister of a small black congregation just as his outspoken anti-apartheid views were making his life difficult as a theology professor at Stellenbosch University.
Nico Smith is part of a growing challenge rocking the NG Church as it prepares for its once-every-four-years general synod in October. Being questioned is the moral and scriptural support the NG Church has provided South Africa's nationalist government, and its apartheid policies, since it came to power in 1948.
The NG Church is the largest of South Africa's three Dutch Reformed churches, claiming 1.7 million followers, most of them in the dominant Afrikaans community. Some historians reckon this church's early missionary policies of preaching in different languages and segregating congregations provided the model for apartheid, or enforced racial separation.
The NG Church is currently divided on racial lines, with separate churches for whites, blacks, Indians, and Coloreds (persons of mixed race).
The NG Church has at previous synods formally rejected racism. A 1974 report on the Scriptures and how they relate to the South African social and political scene rejected the notions that the Bible calls for blacks to remain in a position of servitude or that the whites of South Africa occupy a ''chosen people'' status similar to Israelis. However, both concepts still have some popularity among church members, close observers of the church say.
But the NG Church has found biblical justification for South Africa's policy of ''separate development.'' The church places great literal importance on passages in the book of Genesis where God scatters the people of Babel and splits their one language into a diversity of tongues.
The NG Church says the differentiation of humanity into various languages and nations eventually led to racial differences. And as the 1974 report says:
''The diversity of races and peoples to which the confusion of tongues contributed is an aspect of reality which God obviously intended for this dispensation.''
The church therefore finds there is a scriptural basis for ''autogenous development,'' particularly in a country with as much ethnic diversity as South Africa.
The church does recognize that the Bible teaches an essential unity of mankind, but sees the unity as spiritual and not necessarily one to be translated into human social and political institutions.
The church has offered explicit support of certain nationalist policies. It encourages rapid development of the ''Bantu homelands'' so they can become ''happy homes to the largest possible proportion of the various Bantu peoples.'' It also finds mixed marriages ''undesirable.''
The church qualifies its support of segregation, stipulating that the government should be sure its policy is carried out in accordance with the commandment to ''love one's neighbor'' and that the aim is always toward establishing ''sound interpeople relations.''
The inequality of white and ''nonwhite'' communities in South Africa and the growing racial friction are evidence to church critics that this ''separate but equal'' approach is an unworkable myth.
A recent open letter from 150 ministers to the NG Church condemned it for supporting a social structure based on the ''fundamental irreconcilability of individuals and groups.'' The letter insisted that laws prohibiting mixed marriages and supporting race classification and other segregationist policies could not be defended scripturally.
''We ask what is the thrust and the central message of the Bible,'' says David Bosch, dean of religious studies at the University of South Africa and one of the principal organizers behind the letter. Mr. Bosch suggests the Bible, viewed from a more ''holistic'' point of view urges the breaking down of barriers and the unity of mankind.
No one expects the NG Church to denounce government policy in October. But a reevaluation may come. The synod is expected to consider urging white congregations to stop excluding blacks. And church officials have hinted a separate synod on race relations may be needed this year.
However, such a synod would probably also reflect dissent among church members who feel the church is not pressuring the government to apply apartheid in strict enough terms.
''The attack on the church comes from two sides. There is tremendous pressure from the rank and file for the church to help slow down political developments, '' Mr. Bosch says.
The greatest fear among many informed church observers is that the mounting dissension will produce more inaction than anything else.
''The dissension is not causing people to leave the church, but it has a paralyzing effect on the church, producing more bureaucracy and less leadership, '' a knowledgeable observer says.
The Rev. Mr. Smith's return to a black congregation came as something of a surprise even to him. The Mamelodi Church Council sent him a telegram asking him to be minister. After preaching better relations with blacks for so long, Mr. Smith realized ''it was not possible for me not to accept.''
Still, his arrival at the church was greeted with some wariness by blacks. ''They were very careful and listened to hear what my attitudes were,'' he recalls.
But after two months, church members began to open up. Smith's reception in the community at large has been equally positive with a ''surprising amount of goodwill,'' although Smith sees a small but growing segment of black youth who refuse all dialogue with whites.
Despite myriad social problems, Smith says blacks in his church are most concerned about their relations with whites.
''They experience most severely the fact that they are not acknowledged as people. This to them is the most painful.''