Pretoria's plan to end rent boycott seen as risky. Bill to dock wages likely to spur greater black union activism

The South African government is contemplating a potentially risky move to break one of the most powerful forms of black political protest to have survived the year-old state of emergency. At issue is the widespread refusal of residents in the country's segregated black townships to pay rent or government-service charges. Thus far, efforts to end the protest by evicting defaulters or by setting up payment offices in white areas to counter alleged intimidation by black militants have failed. Officials now hope to get employers to dock paychecks by the amounts owed for rent and service charges.

Legislation to enforce this plan was revealed in Parliament last week. If and when put to a vote, it is virtually assured to pass, since the government holds a great majority in the white chamber.

This could lead to an unprecedentedly stark showdown with black labor unions - by far the most influential black political organizations since the state of emergency began. The unions are riding particularly high these days, after victorious strikes in two different sectors.

A transport strike, settled a week ago, was the more significant victory. Sparked by disciplinary action against an employee who was alleged to have improperly handled $20, the walkout lasted some three months, claimed 12 lives, and became a battle by a militantly antigovernment union for formal recognition by the government-run transport network.

At first, the managers held out. Then, they fired some 16,000 workers, and without major success sought to rehire them over the head of the union. In the end, although without, technically, dealing face-to-face with the union, the transport company ceded all of the union's wage, rehiring, and job-security demands.

In recent weeks, senior government officials have hinted at a long-term campaign to try to ensure that the unions restrict themselves to bread-and-butter issues. But so far, there has been no sign of how this will be achieved. And the introduction of the new bill has drawn predictions from both black activists and independent political analysts here that this move might instead encourage more political activism among unions.

Privately, businessmen are expressing fears that a move to deduct rent payments from pay packets will lead to worker walkouts. Albertina Sisulu, a major figure in the antigovernment United Democratic Front (UDF), sees such a development as inevitable. The rent plan, ``will just start another war between employers and employees,'' she said.

Tom Lodge, a leading academic expert on black politics, says the government's position is made particularly delicate by the limits of its leverage on the unions. The government can - and has moved to - rein in the activities of opposition groups. But to crack down on union activity carries the risk of ``chaos'' in the marketplace, says Mr. Lodge.

The government bowed to energetic overtures from employers early in the emergency and released most of the union officials detained in a general sweep against government foes.

The new rent-collection strategy is an index of the potency of the rent boycott, which began in late 1984 and was a major catalyst in the more general black political unrest that followed. The boycott has continued to a considerable degree despite the emergency restrictions on opposition activities. An estimated $135 million in rent and service charges remains outstanding - forcing the central government to earmark more subsidies for township governments.

The township authorities are meanwhile stepping up their own efforts to break the boycott. In Soweto, the country's largest black urban area, the black local council has warned prominent antigovernment leaders that they face possible eviction if rent remains unpaid. The targeted leaders include Archbishop Desmond Tutu and Winnie Mandela.

Mrs. Mandela, the wife of Nelson Mandela, jailed leader of the outlawed African National Congress, owes the equivalent of about $300. Some urban blacks, who generally earn between $175 and $250 a month if they are not among the large number of unemployed, owe as much as five times that figure.

Journalists in South Africa operate under official press restrictions.