The second most powerful man in South Africa's ruling National Party, Frederick W. de Klerk, told foreign correspondents here today that the government plans to include 10 million of the country's blacks in a "confederal structure" based on the tribal homelands.

De Klerk, who is minister of the interior and leader of the National Party in the dominant Transvaal Province, said blacks would never be included in the new central parliamentary system being established for whites and the minority groups of Asians and mixed-blood people officially designated as Coloreds.

Prime Minister Pieter W. Botha announced plans to set up this new structure, with separate parliamentary chambers for the whites, Coloreds and Asians, to a special congress of his party July 30.

The exclusion of the black majority from this new parliament did not mean the government was "running away" from this aspect of the problem, de Klerk said.

He said about half the black population of 21 million are directly connected to the 10 tribal homelands the government is leading toward independence.

Another 10 million live outside these "national states" in what he called a "situation of dualism," meaning they live and work in the cities of "white" South Africa but have cultural ties with the tribal homelands.

De Klerk said the government aimed to give municipal rights to these blacks in their urban townships, then draw them into a "confederal structure" based on the homelands.

He was not specific about the form this would take, saying it still has to be discussed with the black administrations in the homelands.

Botha is scheduled to hold a summit conference in November with the heads of the four homelands already regarded as independent by South Africa: Transkei, Bophuthatswana, Venda and Ciskei.

"My government feels confederation is a viable option for southern Africa where there is such a complexity of different groups living together," de Klerk said, "and for our region particularly we have decided it is the best option.

"It makes provision for nationalism to come to fruition without destroying other nationalisms, and it also makes provision for cooperation on matters of common concern."

De Klerk emphasized that while his government was committed to reform, it was not moving toward racial integration.

"We have embarked on a policy of dynamic development, but the new government has not changed its basic beliefs and will not change its basic policies," he said, adding that the government's priorities in the new program would include a review of all laws that resulted in racial discrimination, which he argued was different from "racial differentiation."

"Differentiation," he said, was drawing of lines between groups in a multiracial country so each could have security within "spiritual boundaries comparable to the geographic boundaries in Europe." De Klerk said the government was committed to decentralization to improve conditions in the homelands.