Johannesburg — The general synod of South Africa's influential Dutch Reformed Church opened this week with a prayer . . . and a private briefing by the national intelligence service.
It was one example of the intertwining of interests that has made the Dutch Reformed (Nederduitse Gereformeerde or NG) Church something of a strategic ally of Pretoria and brought the church under unprecedented fire as it enters its quadrennial synod.
This synod is regarded here as the most important in the NG Church's history. And since the church represents almost two-thirds of the ruling white Afrikaner population and has historically provided a scriptural justification for the government's policy of apartheid (enforced racial segregation), Pretoria's interests could also be vitally affected by the course of the church.
The synod is expected to swing the weight of the NG Church either behind a ''reformist'' or more moderate form of apartheid, or firmly entrench it behind the more rigid traditional policy of racial separation that the church in fact helped to formulate. A third option would be for the NG Church to evade the central issues now facing it and become less relevant in the South African scene.
The NG Church finds itself almost completely isolated by the world Christian community for its continued support of apartheid. In August the church suffered a crushing blow when the World Alliance of Reformed Churches (WARC) - one of the oldest and largest ecumenical church groups in the world - declared apartheid a heresy. The NG Church was suspended from membership in the organization.
Isolation is not new for the NG Church, which has watched its relations in the world religious community severed one by one over the years. But membership in the WARC was particularly valued, and the rebuke from that body is deeply felt within the NG Church, informed analysts here agree.
Just as serious, the NG Church is faced with serious internal dissent that mirrors the political and racial frictions that are mounting in South African society.
White Afrikaners have just gone through their deepest political division since coming to power in 1948, with the split in the ruling National Party and the founding of the right-wing Conservative Party earlier this year. The NG Church is unavoidably embroiled in the political competition for Afrikaner support, and it is being pressured to take sides through its own policies.
Meanwhile, relations between the white NG Church and the ''nonwhite'' churches for Indians, blacks, and Coloreds (persons of mixed-race descent) - all considered part of the ''family'' of Dutch Reformed churches - are increasingly strained.
Relations are most noticeably deteriorating with the NG Mission Church for Coloreds. There is the threat of a complete break.
A prominent member of this church, Allan Boesak, led a successful campaign in Ottawa to have the NG Church suspended from the WARC.
Dr. Boesak was then elected president of the WARC, and on returning to South Africa he helped persuade the NG Mission Church for Coloreds to take the dramatic stand of declaring apartheid as ''idolatry and a heresy.''
The NG Mission Church for Coloreds went further and said there could only be reconciliation with its ''parent'' white NG Church if it ''confessed its guilt for providing the moral and theological foundations for apartheid.''
All the nonwhite reformed churches have called for an abandonment of the strictly segregated structure imposed by the white NG Church.
Their call for greater unity within the church has been echoed by a growing number of whites. Recently 123 NG Church ministers wrote an open letter to the church categorically rejecting apartheid in church and politics, saying such a policy runs counter to the Scriptures.
The synod will last for 10 days, and most close observers say past experience suggests it will be a cumbersome bureaucratic affair that could evade many of the central issues.
But the chief executive officer of the church, Dr. Pierre Rossouw, said in an interview that the synod would be forced into decisions that would be ''the most far-reaching ever'' for the church.
Specifically, th NG Church synod is expected to debate:
* Whether there should be a move toward a less segregated church structure, bringing some degree of unity among the racially distinct reformed churches.
* Whether the NG Church should continue to support government policy that outlaws marriage between members of different race groups.
* Whether the NG Church should encourage local congregations to allow open services. The church insists its policy is that nonwhites should be allowed to attend white services. But church critics say this happens very rarely in practice because local church congregations have the authority to bar nonwhites from their services.
* Whether African, Colored, or Indian ministers should be permitted to preach to white congregations. White ministers are allowed to minister to nonwhite churches, but the NG Church does not permit the reverse.
One change no one here expects is for the NG Church to unequivocally denounce apartheid. The church does not share the view of many of its critics that apartheid is based on a view of inequality between the races.
''One of the basic mistakes made at Ottawa,'' Dr. Rossouw says, ''was the identification of racism with apartheid; these are not the same things in our mind.''