Black South African townships tense but calm after unrest . . . and Botha gets more power

First and foremost he is party politician. But more and more he fancies himself a statesman. Pieter Botha has been as tough as any of his predecessors in maintaining white power in predominantly black South Africa. But he says there is such a thing as ''healthy power-sharing'' between whites and certain ''nonwhites.''

The prime minister frequently whips up white fears of a Soviet-inspired ''onslaught'' against his country. Yet earlier this year he broke bread with Samora Machel of Mozambique, a country openly friendly with the Soviet Union.

Mr. Botha has produced some surprises since becoming prime minister of South Africa in 1978. But interviews with many who follow his career and an examination of his track record suggest Botha's ''surprises'' are the result of a slightly more pragmatic approach to issues rather than any new ''vision'' of South Africa. By and large, Botha is seen as adhering to the fundamental aims of apartheid.

Today Botha gains more power than he had as prime minister. He assumes the mantle of ''executive state president'' under a new constitution designed by his government and approved by whites. The office combines Botha's previous ministerial job with that of the ceremonial state president.

The most serious immediate task facing him as president will be dealing with unrest among blacks who have been rioting in townships in the Johannesburg area. The reasons for black riots are varied. But the new Constitution, and its exclusion of blacks, is seen by many as one cause of the wave of violence.

The use of new presidential power for good or ill will depends largely on the ''style of leadership'' and the goals of the president, says Dr. Frederik van Zyl Slabbert, leader of the Progressive Federal Party, the main white opposition to Botha's ruling National Party.

At the leadership level of the South African government, there is a ''new style of politics, more pragmatic,'' Mr. van Zyl Slabbert says. But below that level, the ''huge apparatus of the apartheid bureaucracy'' is carrying on with as much determination as ever, he asserts.

The opposition leader claims that under Botha, restrictions on blacks have tightened and forced removals to the so-called black ''homelands'' have continued, despite resistance and international condemnation.

Some aspects of apartheid are likely to come under intense scrutiny next year as a three-chamber Parliament - made up of whites, Coloreds, and Indians - gets into gear. The Parliment, which ends exclusive white rule, is a prime feature of the new Constitution. The body epitomizes some of the apparent contradictions that many analysts believe are a major theme of Botha's rule in that it allows minorities into the government but bars the nation's majority racial group, blacks, from a political role.

The Parliament is to meet informally this week and then assemble formally Sept. 18 for a brief session that will deal mainly with housekeeping matters.

Under the new Constitution, the president is powerful in determining what issues will be dealt with by the white, Indian, or Colored houses of Parliament. Policy regarding blacks, foreign affairs, finance, defense, and law and order, for instance, are ''general affairs'' and must be approved by all three houses of Parliament.

When the three houses cannot agree, the state president will have tremendous power in breaking the logjam in favor of his own white constituency. He can refer all contested legislation to a body called the President's Council, also dominated by whites, for a final determination of whether the bill should be amended, shelved, or passed.

Botha is expected next year to face demands by Colored and Indian members of Parliament that he scrap apartheid laws such as the so-called Prohibition of Mixed Marriages and Immorality acts, outlawing marriage and sex between black and white, and the Prohibition of Political Interference Act, outlawing mixed-race political parties.

The prime minister has paid a high price for the Constitution: He split his party's base of support, the Afrikaner community, which has long regarded unity as the key to survival.

''You can credit the prime minister with considerable courage. He had to say things that in many ways are a heresy within (Afrikaner) political thinking,'' says Desmond Tutu, general secretary of the South African Council of Churches. Botha told fellow Afrikaners there was such a thing as ''healthy power-sharing'' with Coloreds (persons of mixed-race descent) and Indians, albeit under a system that reserves real control for whites.

''But (Botha) stopped disastrously short of what would have provided a resolution of our crisis,'' Bishop Tutu adds. ''What we have is the appearance of power-sharing without its substance,'' he says, referring to the exclusion of blacks.

Helen Suzman, whose tenure in Parliament is second only to Botha's, says Botha is accommodating Coloreds and Indians only to broaden the government's base in order to make the exclusion of blacks more tenable.

Ms. Suzman, a member of the opposition Progressive Federal Party, recalls that Botha was a ''major protagonist'' in the removal of Coloreds from the common voters' roll in the mid-1950s.

Suzman's recollection seems at odds with a story told by Botha admirers that holds he feels a special ''debt'' to Coloreds since a Colored family helped protect his mother during the Boer War of 1899-1902.

Whatever his motives, Botha is seen as so committed to the Constitution that his major preoccupation will be to make it work. This is doubly important given the low voter turnout in recent Colored and Indian elections.

Alfred Ries, an Afrikaner political analyst with Die Burger newspaper, reckons Botha probably sees the new Parliament as his major contribution to South Africa.

''There is no one who knows the inside workings of the (white Afrikaner) politics of this country better than (Botha),'' Mr. Ries says.

As a party organizer Botha earned a reputation as a brawler. One veteran political analyst recalls how he used to deliberately disrupt meetings of opposition parties.

The early years of Botha's premiership were marked by lots of reformist rhetoric, but little action. It appears in hindsight he was consolidating his position in the National Party.

One of Botha's few universally acclaimed moves was to reform South Africa's labor laws in 1979, permitting blacks to organize their own trade unions.

Regionally, Botha has been a hawk. He has put immense political and economic pressure on South Africa's black neighboring states. The results: agreements with Mozambique and Swaziland requiring them not to harbor anti-South African guerrillas, and informal assurances from most other neighboring states, also to deny the guerrillas any military bases.

For the moment at least, Botha has sheathed his sword and is talking more to neighboring black governments.

Botha's government has maintained a steady dialogue with the Reagan administration mainly over the issue of Namibian (South West African) independence. The Reagan administration appears to have accepted Botha's assurances that under certain conditions South Africa would surrender control of the territory.