There is considerable skepticism, in South Africa and abroad, about the power-sharing plan now formally introduced in the Parliament in Cape Town. On the face of it, the constitutional reform would seem to represent a modest step away from the system of apartheid and white racial dominance. For the first time, South Africa's Coloreds and Indians would be given some voice in government through the establishment of three separate chambers of Parliament divided along ethnic lines. At present Coloreds and Indians have no elected representatives.
Yet the deficiencies of the proposed reform are self-evident. Blacks, who constitute 72 percent of the population, would be excluded altogether. Ethnic divisions would be maintained in the government, and whites would retain effective control of the state. A new executive state president would combine the present offices of prime minister and state president and carry unprecedented power, and because the white chamber would have the dominant voice in his appointment he would necessarily be white and Afrikaner. In the eyes of many of mixed race, the reform would thus simply solidify apartheid, in effect widening the ''laager'' to include Coloreds and Indians and staving off the urgent need for black participation.
Perhaps any change, however, is better than no change at all. This seems to be the view of leaders of the Labor Party, the largest political grouping among the Coloreds, who have endorsed the reform despite strong opposition from many members. It is felt that once those of mixed race and Asians have a share in a new ''multiracial'' government, however limited a share, they can work to undo the discriminatory practices of apartheid and win political rights for the black majority as well. Indeed it cannot be ruled out that the reform would unleash new political forces and generate a momentum for peaceful change difficult to stop. Whites might be awakened to the fact that the races can work together; they might begin to shed their fears.
Three important parliamentary by-elections this week in Transvaal Province will be the first test of the ruling National Party's reform initiative. In two of the contests the government candidates are facing a strong challenge from the ultrarightist parties. Defeat of Minister of Manpower S. P. ''Fanie'' Botha, who has done so much to improve South Africa's labor laws, would be a particularly significant blow to the ruling party and its constitutional plan.
The world will be watching the elections - and the deliberations in Parliament on the new bill - with more than passing interest. Few doubt that political changes must eventually come to South Africa.The question is whether they come peacefully - and how they will come.