JOHANNESBURG, AUG. 23 -- As fighting died down in South Africa's black townships today, President Frederik W. de Klerk announced that he would introduce new laws Friday to bring the violence under control.

De Klerk spoke to an audience of several thousand at Potchefstroom University, his alma mater. He gave no details of the new measures, but aides stressed that they would not amount to a reimposition of the three-year state of emergency lifted last month.

The only clue de Klerk offered was that the new laws would affect the control of weapons. Observers took this to mean that he would clamp down on the right of Zulu tribesmen to carry sticks, clubs and spears, which the government has so far allowed in the name of preserving tribal culture.

The 11 days of fighting has chiefly pitted supporters of the African National Congress against backers of Zulu Chief Mangosuthu Buthelezi's rival Inkatha movement, and many Zulus have been seen carrying such weapons openly through the streets without police intevention.

Sporadic violence continued overnight and this morning, especially in Kagiso township, west of Johannesburg, where 18 people died, raising the overall death toll in the townships to 528 since the fighting began.

But by tonight, police reported all quiet in the chain of townships along the 150-mile gold-mining reef of the Witwatersrand region, which has Johannesburg at its hub.

The respite, the first in the worst sustained violence in South Africa's history, coincided with calls for peace from church leaders and from Nelson Mandela, deputy president of the African National Congress, who appealed in a television broadcast tonight for the warring factions to lay down their arms and said his organization was working behind the scenes to achieve peace with Inkatha.