SOWETO, SOUTH AFRICA, JAN. 9 -- A brief legal notice in yesterday's official government Gazette speaks volumes about what happened to the black revolution that appeared to be taking hold across South Africa just 18 months ago.

The notice declares that all public meetings in Johannesburg and nearby Roodeport to celebrate the 76th anniversary of the African National Congress or the release from prison of ANC Chairman Govan Mbeki have been banned by Acting Police Commissioner Lt. Gen. Rudolph Jansen van Vuuren.

The striking thing about the notice is that no organization has publicly called for a meeting in Johannesburg or Roodeport to celebrate the ANC's anniversary.

This suggests that security police, who routinely infiltrate hundreds of antiapartheid groups, may have gotten wind of incipient plans for such a demonstration and banned it even before it could be announced.

The brief item in the Gazette illustrates how effective the government has become in stifling dissent against its policies in the past year and how intimidated organized opposition groups in South Africa have become.

As the whites-only Parliament prepares to reconvene in Cape Town next month, there is increasing speculation that the ruling National Party, led by President Pieter W. Botha, is considering strong measures to restrict even more the activities of such legal opposition groups as the United Democratic Front (UDF) antiapartheid coalition and the black Congress of South African Trade Unions (COSATU).

But any new measures would appear almost to be superfluous, given the pervasive effects of the nationwide state of emergency imposed by Botha on June 12, 1986, after an unprecedented two years of social and political upheaval throughout South Africa.

The pulse and temperature of that upheaval dropped dramatically during 1987, taking the South African story off the world's television screens and newspaper front pages and leaving the often mistaken impression abroad that the draconian press censorship rules that accompanied the emergency have masked continuing antigovernment turmoil in the black townships.

While press restrictions have been severely applied, particularly to the South African media, the reality is that the harsh enforcement of literally hundreds of other national security statutes and emergency regulations has, to a large extent, put the lid on organized protest against the apartheid system of racial separation and continued white minority rule.

People who made news by challenging the authority of the government began disappearing from the scene, and events that had made news stopped happening.

With the exception of internecine fighting among rival black political groups in Natal Province, which last year left more than 280 people dead, political unrest in the country's black townships declined dramatically during 1987.

Because Law and Order Minister Adriaan Vlok decreed in October that it is not in "the interest of the country" to release cumulative statistics, precise figures of deaths, injuries, arrests and property damage during the past year are not available.

The only official barometer of antigovernment violence is the daily police report, which, excluding the recent escalation of "black-on-black" factional fighting in Natal, has indicated a sharp decline in unrest-related deaths and injuries.

While political violence claimed 1,289 lives in 1986, many of them in security force actions during township riots, the official reports suggest an average monthly death rate of less than 20 in 1987.

Because of the difficulties in obtaining reliable figures, the independent South African Institute for Race Relations stopped publishing statistics on fatalities in October. But it said that in the first nine months of 1987, 264 people died, for a monthly average of 29.

In contrast, the average monthly death rate for the first six months of 1986 was about 150, according to the institute.

"Any objective observer would have to conclude there has been a dramatic decline in unrest. The emergency clearly has worked," the director of the race relations institute, John Kane-Berman, said.

He noted that a pattern of hit-and-run attacks on black policemen and township councilmen had replaced the familiar cycle of clashes with white security forces, followed by mass funerals and still more clashes as the main cause of fatalities.

Unrest-related arrests and detentions without trial, which in 1986 totaled 11,006 and 30,163, respectively, according to independent monitoring groups, also dropped sharply last year. The Detainees' Parents Support Committee estimates that about 1,500 people are currently in detention under emergency regulations and another 350 are being held under other security legislation.

Nongovernment experts on black politics and unrest in South Africa generally agree that the lowering of the revolutionary climate last year cannot be traced to a single factor, but instead was the result of a number of developments. Some of these include:Collective battle fatigue among young black militants -- the "comrades" -- who turned the townships into battlegrounds until the massive force of Army troops and riot police crushed their rebellion in the streets. This has been accompanied by a general lowering of expectations that the white regime in Pretoria could be overthrown by force.

Already, people in the townships speak of "the time of the comrades" as if it were a part of history. The imposition of sweeping new emergency regulations that, in effect, made any form of civil disobedience or organized opposition to government policy illegal if so decreed by a police officer of any rank.

The banning of organizations that the government decreed were fanning the revolutionary climate. Increasing sophistication of police tactics. The detention without trial of thousands of militant black leaders who gave direction to organized protest in the townships.

The dismantling of "street committees" that effectively had replaced official government structures. Effective use of a policy of co-option, in which millions of dollars have been pumped into townships such as Pretoria's Mamalodi and Johannesburg's Alexandra to upgrade education, housing and public utilities in an effort to "win the hearts and minds" of moderate blacks. A decision by antiapartheid groups to end a massive school boycott and encourage young blacks to return to the classrooms, thereby taking thousands of potential combatants off the streets. An increase in real income of those blacks who are employed, even though joblessness has risen, and an increase in the number of blacks allowed by the state to purchase their township homes. A backlash by some moderate blacks against the constant disruption of their lives brought about by violent protest.

Here, in South Africa's largest township, a sprawling area southwest of Johannesburg, there is a prevailing sense of the popular rebellion being on hold at least for the duration of the emergency, accompanied by an awareness that it could flare up again.

With so many militant leaders driven underground or detained, young militant blacks acknowledge their war weariness and speak vaguely of a period of "consolidation" and the formulation of new strategies.

"It may be quiet now, but a lot is going on behind the scenes. The struggle is not over yet," said a teen-age militant who claimed to have been detained twice since the emergency was imposed.

Isaac Meletse, who runs a criminal rehabilitation project in Soweto, emphasized the importance of a broadening black middle class on stabilizing the townships.

"All you have to do is drive around here and see all the work going into these little houses. If you see a man putting an addition onto his house, you know he's a new homeowner. He's got a mortgage to pay, and this calms things down," Meletse said.

Kane-Berman of the race relations institute said, "We have always argued that if you want political stability in South Africa, you have to start by giving people a stake in life. They should own their own homes, and, fortunately, that is beginning to happen."

Michael Hough, director of Pretoria University's Institute for Strategic Studies, said he believes that a change of strategy by leaders of the liberation movement in exile also has contributed to a dampening of the revolutionary climate here.

"While the ANC still talks about making South Africa ungovernable, there is a realization that forcible seizure of power is not possible. They may still have hopes for a mass uprising, but they tend to concentrate more now on trade unions and sanctions -- to make South Africa unprofitable rather than ungovernable," Hough said.

Both Hough and Kane-Berman stressed the importance of the economic cycle on political unrest, saying there is less likelihood of instability during periods of economic recovery such as the one at present.

"If living standards take a big dive in a couple years' time and there is a volatile situation in that underlying grievances have not been addressed, you just need some incident to spark it off again," Kane-Berman said. "That danger always exists."