JOHANNESBURG, AUG. 15 -- Troops moved in today to try to restore order as fighting between rival black groups swept through three densely populated townships southeast of Johannesburg, leaving a trail of devastation and more than 100 people dead on South Africa's bloodiest day in many years.

Police spokesman Eugene Opperman confirmed that the overall death toll in the fighting, which began Sunday night but reached a crescendo today, was at least 140, and estimated the number of injured during the period at more than 1,000.

The cause of the fighting remains unclear. Police describe it as a clash between members of the Zulu and Xhosa tribes, but leaders of the African National Congress and its allied organizations said it was an extension of the black civil war in Natal province between their supporters and members of Chief Mangosuthu Buthelezi's Zulu-based Inkatha Movement.

Speaking at a news conference here, Chris Dhlamini, vice president of the country's major labor union federation, Cosatu, an ANC ally, accused Inkatha of launching "an orchestrated campaign to export the battle from Natal to Transvaal {provincial} townships to fight for Inkatha's existence in the political arena."

The ANC's information chief, Pallo Jordan, accused police of aiding "Inkatha vigilantes" in the fighting, and charged President Frederik W. de Klerk with failing to control and discipline the police force.

In a statement from his headquarters in Ulundi, Buthelezi denied that Inkatha was promoting the violence, which he said appalled him. He called for black leaders to convene peace talks.

In a statement tonight, Law and Order Minister Adriaan Vlok urged black political leaders to use their influence to try to end the fighting, which began in a migrant workers' hostel in Thokoza township.

Alfred Nkambuli, who lives in the hostel, said the violence was sparked by a dispute over a dice game that led to one of the hostel dwellers being killed by a man from a nearby squatter camp called Phola Park.

Other hostel dwellers then raided the squatter camp, setting fire to shanties, Nkambuli said. From there the fighting spread, with the squatters mounting a reprisal raid on the hostel.

As further counterattacks followed, the struggle seemed to take on a political flavor: most of the hostel dwellers are Zulu migrant workers from Natal, while most people in the shanties are from other tribes.

By last night, the death toll in Thokoza had reached 15, but the fighting intensified overnight, and by this morning police reported 38 dead.

Today, it spread to the neighboring townships of Kathlehong and Vosloorus. As the warring groups rampaged through the streets attacking one another and setting fire to homes and shops, thousands of residents, many of them women and children, fled to the surrounding countryside.

Reporters who visited the area saw groups of up to 2,000 men moving through the streets armed with spears, axes, machetes, butcher knives, sticks, iron bars and home-made shotguns with barrels cut from steel piping. Police said more sophisticated weapons also were used, including heavy-caliber pistols and hand grenades.

Reporters in Thokoza saw a group of youths chase a man down a street, pull him to the ground, stone him, douse him with gasoline and set him ablaze.

Two reporters ran to the burning man and put out the flames. Police later took the man to a hospital, where his condition was described as critical.

As the casualties mounted, truckloads of troops moved in to the three townships late today to try to keep the warring factions apart. Police moved from house to house searching for weapons and disarming fighters.

The publicity secretary of the Vosloorus Civic Association, Keith Montsitsi, announced that his organization was attempting to arrange peace talks between leaders of the warring factions later tonight.