South African Blacks' New Tactic Fazes Pretoria. Sowetans' readiness to negotiate may signal political watershed. NEGOTIATING FOR GAINS

SOWETO, usually a bellwether of political change in South Africa, is proving so once again. The issue this time is a 31-month-old rent boycott. Black councilors charged with running the sprawling township recently struck a deal with opposition activists, in principle, to write off the $70 million owed in arrears by residents. The accord's significance, however, goes far beyond just big bucks.

For starters, it sets the stage for a possible showdown with the government. Pretoria doesn't like it because the deal negates its carefully constructed counterinsurgency strategy. Part of that plan calls for the installation of ``moderate'' black leaders in town councils to neutralize anti-apartheid ``radicals.''

But by meeting with these activists last month and cutting a deal, councilors have conferred on them the very legitimacy they were meant to destroy. Quashing the agreement, however, could be a problem for Pretoria. That's because it long has insisted black local authorities - as councils are called - are truly independent.

Perhaps more important, analysts say, the accord also marks a watershed in black politics.

For years, activists have refused to bargain with the government, claiming that would be tantamount to selling out. They instead stuck to boycott tactics - tactics rendered just about ineffective by the state of emergency that was slapped on in 1986.

Activists since have been searching for new strategies. And they finally seem to have hit on the idea of negotiations, which will allow them to deliver short-term benefits along the same lines as trade unions. It's a tactic that ``could change the direction of black politics,'' says a Johannesburg political scientist who asked not to be named.

``This isn't a confrontation strategy designed to bring down the government,'' he continues. ``It's a negotiation strategy that will make gains through collective bargaining. And it will reinforce the idea that further negotiations could lead to even greater gains.''

That wasn't necessarily the boycott's intent when it started in 1986. An estimated 2.5 million people live in Soweto, and many simply were fed up with years of forking over relatively high fees for miserable, tumble-down hovels. They say they paid off their homes, in effect, long ago.

Their determination at times caused the boycott to become nasty. Frustrated in attempts to break the strike, town councilors started evicting residents. That led to street battles, petrol bombings - and the loss of some 30 lives. To complicate matters further, the government earlier this year banned many of the opposition organizations that were key to trying to work out a solution.

So by the time last October's municipal elections rolled around, Soweto was in a real mess. Along came the candidates of Sofasonke, a populist party founded in 1942 to deal with the problems of the then-fledgling township. Because the incumbents had been Sofasonke members once (the party had split with them), the new candidates made clear they stood on the opposite side of the rent issue.

And that's how they won. ``We promised not to evict people if we were elected,'' declares Samuel Mkhwanazi, the new, gravel-voiced mayor. ``We think these houses belong to the people.''

(Mr. Mkhwanazi himself didn't exactly receive an overwhelming mandate. Activists staged a relatively successful nationwide boycott of the elections, contending that they granted legitimacy to an illegitimate system. In Soweto, only about 11.5 percent of elegible voters voted.)

Anti-apartheid groups - which had refused to meet with provincial officials to discuss the rent issue - clearly saw in Sofasonke an overlapping of interests. Thus, Mkhwanazi was approached by a delegation that included such prominent leaders as Anglican Archbishop Desmond Tutu; the Rev. Frank Chikane, general secretary of the South African Council of Churches; and Cyril Ramaphosa, general secretary of the National Union of Mineworkers.

At a press conference afterward, the delegation announced the agreement-in-principle. Besides the arrears issue, the council also said it would reevaluate utility rates and consider transferring ownership to longtime residents.

The accord ``caught us completely off balance,'' says Victor Milne of the Transvaal Provincial Administration, the governmental body responsible for Soweto. Although Mr. Milne says it's up to the council to decide about writing off the arrears and lowering rates, ``if they do, they haven't a clue how to run Soweto.''

For starters, Milne figures the average Soweto home uses about 51 rands ($21) worth of electricity each month. That already is twice the 25 rands the council proposes to charge each household for everything: electricity, water, and the like. Moreover, the council owes the province close to $80 million in bridge financing - a bill that will be impossible to repay if rent arrears are written off.

Milne says Soweto needs to generate about 13 million rands monthly just to break even; it currently is getting only 3 million rands. ``He who pays the piper calls the tune,'' Milne warns. ``If we cut the council off, they'll collapse.''

The Johannesburg political scientist thinks the government will use financial pressure to get councilors to back down from the agreement. But he believes that Pretoria's military men - the counterinsurgency strategy's designers - are even more upset by the pact's political implications.

``The military guys are tearing their hair out,'' he says. ``Talking with activists is the antithesis of what they intended.''

For the moment, Mkhwanazi and his councilors are keeping quiet about a final decision, meeting with community groups to hear their opinions. Privately, Mkhwanazi says that ``We're testing the government. Now we'll see if it's true that black local authorities really can make their own decisions.''

As for anti-apartheid activists, the matter is a test case. Regardless of the outcome, they reckon they've won at least provisional concessions from the authorities. We're national leaders, Reverend Chikane has said, and this could have national implications.