Johannesburg — In the space of one week, South African Prime Minister Pieter W. Botha has been told his new proposals for limited ''power sharing'' with Indian and mixed-race minorities have: (1) a clear mandate from whites and (2) no mandate whatsoever.
Such are the mixed signals coming from South Africa's increasingly splintered white electorate, which, although a minority, holds the reins of power that will determine the extent to which change comes here through consent or force.
Meanwhile, blacks representing 70 percent of the population watch the growing wrangling among whites with interest and frustration.
''It is a bit eerie,'' says a politically astute young black. ''All this wrangling is about us, but no one consults us.''
Indeed, Mr. Botha's proposals for giving central government representation to Indians and Coloreds (persons of mixed racial background) have alienated right-wing support on the grounds the plan is the initial step toward ultimately sharing power with blacks. Mr. Botha staunchly rejects any such possibility.
Still, that basic fear apparently galvanized a strong right-wing showing in a provincial by-election last week. Botha's ruling National Party turned in a weak performance in its first electoral test against the new Conservative Party, formed by breakaways from the National Party earlier this year. The Nationalists scraped by with a narrow victory in the industrial district of Germiston, which has long been a National Party stronghold.
Just as worrisome for the National Party was the fact that the total right-wing vote, represented by the Conservative Party and the extreme right Herstigte (Reconstituted) National Party, exceeded its own tally.
''The prime minister clearly has no mandate to go ahead with his reform policy,'' pronounced Conservative Party leader Andries Treurnicht.
Political scientists are more cautious in their analysis, particularly in light of an important nationwide opinion poll published days before the Germiston election.
That poll showed strong white support for Botha's proposed constitutional changes, with 55 percent of the respondents backing the plan. The largest slice of white opinion - 46 percent - said the exclusion of blacks from the ''power-sharing'' proposals was bad.
The exclusion of blacks has led to intense debate among whites over whether the plan is really a progressive step. The official opposition Progressive Federal Party has rejected the plan in its current form partly because it is seen as a recipe for further polarizing black-white relations.
Botha's biggest problem will be selling the plan to Coloreds and Indians, who are hungry for a political platform but will be seen as sellouts by many blacks if they participate. The poll found an overwhelming majority of Coloreds and Indians favoring the inclusion of blacks in any new constitutional setup.
Most Indians and Coloreds would not vote in favor of the constitutional changes as they now stand, but clear majorities of both groups clearly favored negotiating with the government toward improving the ''reforms.''
Although the Germiston vote and the poll may appear at odds, they may just reveal that ''whites today are a mixture of confusion and anxiety, saying many different things,'' says opinion specialist Lawrence Schlemmer of Natal University.
He says the election provided ideal conditions for a large protest vote. A working-class district hard hit by South Africa's slumping economy and raging inflation, Germiston is ideologically conservative, offering precisely the kind of electorate that will find the new Conservative Party appealing, Schlemmer says.