White South Africans vote for 'reform' -- but disagree on what it means

South African whites appear to have voted in favor of ''reform'' in a handful of by-elections Nov. 3. But they also seem to remain deeply divided over what reform means.

Is it a process of change ultimately leading to resolution of the central problem here of enfranchising blacks in some meaningful way? Or is it a process of adaptation to entrench white supremacy in South Africa and ward off black power?

The sweep by the country's ruling National Party of the six out of seven by-elections it contested stemmed in large part from the party's ability to studiously avoid answering those questions, analysts here say. Voters were left to draw their own conclusions and were apparently content to do so as they gave what analysts here interpreted as strong support to Prime Minister Pieter W. Botha's proposals for limited ''power-sharing.''

Botha's program for ''power-sharing'' calls for Coloreds (persons of mixed race descent) and Indians to participate in central government. It offers nothing in the way of political power to blacks, who are 70 percent of the population.

The proposals are expected to be taken up by Parliament next year.

Most blacks see the plan as a white attempt to coopt Indians and Coloreds into a unified front against blacks. The white opposition Progressive Federal Party (PFP) has rejected the ''reforms'' for excluding blacks and leading to greater white-black polarization.

But the greatest fear among the Afrikaners who dominate white politics is that ''power-sharing'' is just the first step to granting power to blacks. Fearing this, right-wing Nationalists split and formed the Conservative Party earlier this year.

The outcome of the by-elections appears to signal that the National Party has contained its threat from the right while earning some grudging support from critics on the left.

This was possible because voters in various constituencies saw ''reform'' as meaning different things. Conservative whites appear to have contented themselves that ''reform'' is not the ''thin edge of the wedge'' leading to some form of power-sharing with blacks. More liberal whites seem to have accepted that this small change is better than nothing.

The results in the three most important parliamentary races (in all there were seven parliamentary and provincial contests) indicated the National Party's ability to contain the right and gain some strength from the left.

* Perhaps the most important race was for the parliamentary seat in Parys, a farming area. It was here that analysts expected any significant shift among conservative Afrikaners to the Conservative Party would occur.

But the Nationalists won the seat by a comfortable margin over the Conservatives. Political analysts reckon voters supported the National Party through loyalty and a conviction that Botha-style ''reform'' would not threaten the basic structure of apartheid.

* The Nationalists scored another impressive victory in Stellenbosch, a university town that has been the spawning ground of liberal or ''verlig'' Afrikaner thought. The party increased its margin over the more liberal PFP, compared to the 1981 election. Analysts read this as a signal that some left-wing support was going to the National Party because its ''reform'' policies were a tentative start that required support to expand. The vote appeared to be a setback to the PFP, which has called for white opposition to Botha's ''reforms.''

* PFP's opposition policy seemed to get a cool reception from voters in a Johannesburg constituency that had been a PFP stronghold.

The Nationalists did not contest the seat, but the PFP fell far short of the support it gained in 1981. There was a low turnout at the polls, apparently a sign of voter apathy.

While analysts see this by-election as encouraging the government to proceed with its ''reforms,'' the votes tallied by the Conservative Party and the further-right Herstigte (Reconstituted) National Party suggest the National Party dare not go any further with its ''power-sharing'' proposals. In Parys, for example, the combined right-wing vote of the CP and HNP was only 10 votes short of the NP total.

While leading Indian and Colored political parties have not taken a final stand on the ''power-sharing'' proposals, they appear to be pressing for more concessions that would help them cope with extreme pressure from blacks to reject the whole concept. But these by-elections indicate the government will be reluctant to go any further with its ''reforms'' at this time.