SOUTH AFRICA'S white electorate decided last week to vote in favor of Prime Minister P.W. Botha's plan for limited constitutional change, an outcome Botha hailed as a "victory for South Africa." But the measure made no provision for the 22 million Blacks living within South Africa's traditional borders, and will further enshrine apartheid rule.

Two-thirds of the 2.7 million eligible white voters favored the new constitution, which had been hotly debated among white Nationalists. The approved plan allows for an executive white president with potentially authoritarian powers--he would be able to dissolve Parliament and declare martial law--and a three chamber legislative body composed of whites, Indians and coloreds (those of mixed blood) in separate chambers. Blacks, of course, will still be excluded. Parliament will be dominated by whites through a system of weighted votes that ensures the election of an Afrikaner to the position of authority, giving Afrikaners, who have dominated the country since 1948, a larger, though still bogus, mandate.

Botha's new system divides nonwhites to insure white dominance--the strategic base of apartheid. The "yes" vote has also insured Botha a ticket to a future Presidency. Even more moderate South Africans joined supporters of the referendum, hoping that a large majority consensus would force Botha actually to step on the road to reform he has promised potential sympathizers in the West.

But it is more likely that Botha, who has dedicated his life to preserving apartheid, is not lying when he says that "there is no hidden agenda" for the later inclusion of Blacks in the political process. Botha will put up a colorful camouflage by incorporating those of brown colored skin, but he has already said that Blacks will not be given full political rights in his childrens' lifetimes (parroting a statement made by former Rhodesian leader Ian Smith shortly before Blacks took control). Instead Blacks, who from a majority of the population, will continue to be consigned to non-citizenship status through the homeland system, nominally independent government established tribal states ruled by puppet chiefs.

THE SOUTH AFRICAN government will now have a larger group to draw on for mandatory military conscription. Combined with the power of the president for martial law, the new constitution is simply an effort at modernizing the existing apartheid system.

Some suggest that Botha must now answer with reforms to satisfy the constituents who voted "yes," while still trying to satisfy the substantial minority of Afrikaners who voted against "reform." But Botha has already hinted that his main concern has been to please the West, especially President Reagan.

The constitution passed last week makes no provision for the so called urban Blacks who have supposedly lost their tribal roots and are allowed to live in the cities, instead of being tied to a "homeland."

The supposed winners from the reform--Indian and colored voters--are now placed in an unpleasant buffer position. Many of their leaders have urged a boycott of the segregated chambers of Parliament, while others are more willing to lay down for their former oppressors. So a new twist is added to apartheid.

The U.S. government--the only international voice to speak out in favor of the referendum--will also toe the new South African line. With the advent of the Reagan Administration a pattern of "constructive engagement" with South Africa reversed the legislation of the Carter era. Although the House voted last week to put severe restrictions on future American loans and investments to South Africa, most Americans still cling to the overly pessimistic view of peaceful change in the country.

If nothing else, Botha and his lot were reaffirmed by the "yes" vote last week. It's too much to hope that the U.S. will get out of South Africa, and its willingness to take some credit for Botha's so called softening of apartheid indicates that the U.S. is as entrenched as ever.

What should be recognized is that this constitutional move, while polarizing whites, was denounced unilaterally by puppet homeland chiefs and leftist African National Congress members alike. It was a remarkable show of unity from groups that historically have been at odds. The threat of a unified 22 million Blacks in South Africa will inevitably have to be reckoned with and no token reforms can make their persistent threat of resistance vanish.