SOWETO, SOUTH AFRICA, JUNE 16 -- An estimated 1.5 million black workers in the segregated townships of South Africa stayed away from their jobs today to commemorate the anniversary of the 1976 Soweto student uprisings, which led directly to the most intense racial unrest this country has ever experienced.

A choking pall of coal smoke from kitchen fires hung over nearly 1 million matchbox-like brick houses on a crisp winter day, as heavily armed security forces blockaded the entrances to this satellite ghetto of 2.5 million blacks in an attempt to stifle organized dissent.

Soweto's streets were eerily deserted, as commuter buses and jitney taxis shut down their operations to mark the day 11 years ago when black students defied an order to learn Afrikaans -- the language of the dominant, Dutch-descended whites -- and demanded better education for blacks.

When security forces opened fire on the students that day, they left a 13-year-old boy dead in the first salvo. That killing sparked 15 months of unprecedented rioting that spread to other townships and resulted in more than 600 blacks being killed in the first three months alone.

The ensuing revolt was not put down until October 1977, when the government outlawed 21 major antiapartheid organizations, forcing about 4,000 young blacks across South Africa's borders into exile with the outlawed African National Congress. By then, an estimated 1,700 persons had been killed in South African rioting, a figure that has grown to more than 2,500 since 1984.

As a result, the Soweto uprising anniversary is the most important on the black political calendar in South Africa. A year ago today, 11 persons were killed and hundreds of black leaders were detained during protests to mark the occasion.

In contrast, the major antiapartheid organizations today called on their members to exercise restraint and observe the anniversary with quiet dignity. There were no serious clashes with security forces, and no reported casualties.

No buses were running into Soweto this morning to take workers to their jobs in central Johannesburg factories and to the white suburbs north of the city.

Officials said that Johannesburg-bound trains on the Soweto line carried only 5 percent of the normal passenger load. Virtually all businesses in Soweto were closed, following an appeal by the township Chamber of Commerce for traders to pull down the shutters of their shops.

Churches across the country tolled their bells at midday, and thousands of blacks gathered for solemn memorial services.

In Tembisa, a sprawling township halfway between Johannesburg and Pretoria, white security forces implored residents over a loudspeaker to go to work. But only small numbers of workers obeyed, despite police promises of protection.

In Soweto, police appeared at the Regina Mundi Catholic Church -- traditionally a focal point for antiapartheid demonstrations -- shortly before the beginning of a commemorative service, but left at the request of participants.

Before leaving, however, they confiscated protest posters hung by the National Confederation of Trade Unions, a black consciousness labor federation.

At the Evangelical Lutheran Church in Soweto's White City, Rapu Mokolane, a leader of the 1976 uprising and now general secretary of the South African Youth Congress, led an emotional rally in defiance of a government ban on political meetings.

Meanwhile, the government said it had banned posters prepared by an extremist white group calling for the deportation of all non-whites from South Africa.

The government Publications Control Committee ruled that the poster, issued by the White Liberation Movement, a splinter faction of the neo-fascist Afrikaner Resistance Movement, was undesirable. The government ordered that all copies of the poster, which reads "Stop Terror -- Repatriate All Non-Whites," must be removed from public places.