NEITHER the United States nor South Africa should overreact to the setback suffered last week in that country by its ruling National Party. Although a far right-wing white party took one of the five parliamentary seats being contested in a mini-election and a second conservative white party almost won another, the National Party still retains ample room to maneuver. The National Party unexpectedly lost its single seat in a rock-ribbed blue-collar constituency in which a racist slogan -- ``Don't think, shoot'' -- mobilized voters opposed to the official policy of gradual governmental-led reform.
The herstigte (reconstituted) National Party had never taken a seat from the National Party before. But the fact that it did so in Sasolburg, where coal is gassified into petroleum, hardly threatens either the National Party's massive majority in the white chamber of South Africa's threefold (white-Colored-Asian) legislature or its hold on the votes and opinions of the mass of the country's voters. The loss of Sasolburg acknowledges the persistence but not the predominance of ex treme racist views among whites. Moreover, a general election is not required before 1989.
Given the character of mid-term mini-elections in South Africa, policymakers in both Washington and Pretoria should not worry unduly about the National Party's losses. Nor should they worry about its near defeat in Springs, east of Johannesburg, another working class constituency.
The National Party easily vanquished its more conservative opponents in Vryburg, a depressed rural farming area, and Bethlehem, a more prosperous farming center in the Orange Free State. It defeated both a more liberal, Progressive Federal Party, challenger, and two conservative opponents, in the English-speaking constituency of Port Natal.
These clear victories, as well as the narrow one in Springs, indicate that a white government which has demonstrated its inability to curb massive violence by Africans or to provide a recognizable blueprint for reform still has support among the broad run of white voters. Further, despite President Pieter W. Botha's clear loss of personal legitimacy as a leader in the white business community, it is clear that ordinary white voters still find options to the left and right of his party too dangerous to c ontemplate.
By maintaining his hold on the white electorate tolerably well, Mr. Botha can no longer claim that if he reforms South Afica too quickly whites will rebel, and desert his party. The message of last week's election is that whites still expect the National Party to save them and save South Africa.
Mr. Botha has a mandate for rapid reform. With these bi-elections behind him, and a serious liquidity crisis preoccupying his country's central bank, Mr. Botha can and should call his parliament into emergency session. Its next regular meeting begins in late January. By proposing a legislative framework and timetable for the dismantling of South Africa's system of apartheid he might be able to persuade both outsiders (especially creditors) and -- more important -- African rioters that meaningful reform is still possible. South Africa is ready for change of a kind that Africans demand. They seek clear progress toward full political participation for Africans. Yet they still -- but less with each passing day of violence -- might take less than ``one man, one vote'' or complete majority rule providing that whites demonstrate a desire to share power.
After last week's poll Mr. Botha is strong enough to initiate such discussions.
If President Botha balks, misreading the lesson of the recent election results, or remains complacent while the townships burn around him, then local white businessmen and the international corporate community will walk away from South Africa.
The Reagan administration, timorous and tentative when it should be resolute, might even be compelled by an enraged Congress to terminate its last ties to a white regime which lacks the leadership to understand and build constructively upon a continued if reluctant support of white voters at the polls.
Robert I. Rotberg is a professor of political science and history at the Massachusetts Institute of Technology.