S. African election: key indicator of support for Botha. Future of reform seen tied to incumbent policy and vote pull

South Africa is gearing up for what promises to be one of the least suspenseful, yet most important, white elections in its history. The outcome of the vote is expected to matter less than the margin, and platform, with which the incumbent government of President Pieter Botha secures victory. Local pundits are united in predicting triumph for Mr. Botha's National Party, which has ruled for nearly four decades. Still, he faces an assertive challenge from minorities on both the left and the right to his strategy of gradual race-policy reform.

It was in an apparent bid to undercut these critics that the President used a televised speech on New Year's Eve to announce elections for the coming year. They are expected to be held sometime this spring, about two years ahead of schedule.

The extreme right charges that Botha has gone much too far in dismantling apartheid, the policy of enforced racial segregation that the National Party began assembling in the 1940s. But the white liberals - partly in attempted proxy for a black South African majority that has no voice in Parliament - argue that Botha has not gone nearly far enough on reform. Moreover, the President faced similar criticism this past weekend from an unfamiliar source: the head of a mixed-race ``Colored'' party that had joined in his pioneering 1984 expansion of Parliament to include nonwhites (but not blacks).

The National Party's campaign strategy - and the relative success of right and left in confronting it - could help determine the pace and extent of future reforms.

Particularly important may be the returns from Natal Province. This is the province, among South Africa's four, in which the white-liberal opposition is strongest. The Natal liberals seem in no position to challenge Botha's overall parliamentary majority. But having recently helped negotiate a milestone blueprint for power-sharing with the region's black majority, they are determined to make national government endorsement of the plan their major campaign issue. So far, the government has seemed reluctant to go along with the plan, although not rejecting it outright.

The timing of the national election - and Botha's remarks in announcing it - suggest he will seek a revived mandate for measured reform, coupled with an unflagging clampdown on the black political unrest of the past two years. Botha announced the vote amid a state-of-emergency counter-offensive against unrest at home and criticism from abroad. The theme of his year-end talk to the nation was unity: unity against black militancy or violence, and international criticism or economic pressure.

The emergency clampdown seems to have slowed the momentum of the extreme right - notably a Conservative Party founded by National Party breakaways several years ago. The continuing antigovernment pressures inside South Africa and abroad, meanwhile, are seen as complicating any bid by the white-liberal Progressive Federal Party to win support for greatly accelerated reforms.

Still, spokesmen for both the Conservative Party and the Progressive Federal Party say they are determined to fight the President every step of the campaign trail - even if this means violating recently tightened restraints on public references to antigovernment unrest.

Political analysts say that both opposition parties stand a chance of making inroads into the National Party's commanding parliamentary majority - now 127 of 178 seats. But, they add, the degree of success will depend on a number of factors - most important unrest and the economy - as the election approaches.

Key questions about these factors are:

Will political unrest, beginning to flag under state-of-emergency pressures, continue to do so as the election nears?

Will a recent mini-rebound from the country's worst economic recession on record continue?

This report was written to conform with South Africa's press restrictions