JOHANNESBURG, SEPT. 14 -- Three suspected guerrillas of the outlawed African National Congress were tracked down and shot dead in a gun battle with security forces near the Zimbabwean border, the military command said today.

One of the gunmen was killed in a shootout Friday night on a farm near Alldays, in the northern Transvaal Province, and the other two were killed on another farm in the Pontdrif area Saturday, the South African Army said.

The gunfight Saturday occurred after a farmer reported the presence of "suspicious people," authorities said. The military command said security forces suffered no casualties and captured three Soviet-made automatic rifles, eight pistols and hand grenades and other weapons.

An Army spokesman said the three gunmen had "infiltrated from Zimbabwe."

South Africa has repeatedly justified its military incursions into neighboring Angola, Zimbabwe, Zambia and Mozambique on the basis of allegations that ANC guerrillas trained in those countries cross the borders to conduct terrorist operations in South Africa.

Independent military analysts estimate that at any given time there are between 300 and 500 ANC guerrillas operating in South Africa, but counterinsurgency experts in the South African Police Force say that the estimates are exaggerated and that only about 50 trained guerrillas operate inside South Africa at a typical time.

In its daily report on violence, police headquarters in Pretoria today said a bomb damaged a power substation in Johannesburg's black township of Soweto yesterday. The authorities did not say who was responsible.

Police also said security forces fired shotguns and tear-gas grenades after a crowd of mixed-race Coloreds stoned them near Saldanha, north of Cape Town, yesterday. Four persons were injured and four arrested in the clash.

The police command also said an intensive search was under way for gunmen who killed two white policemen -- a father and his son -- in the tribal homeland of KwaNdebele, north of Pretoria, Friday night.

Authorities said the bullet-riddled bodies of police Lt. Hannes Fourie, commander of the KwaNdebele National Guard, and his son, Constable Mark Fourie, were found near where they had gone to investigate a report of a robbery.

A police spokesman said they were shot at point-blank range with an AK47 assault rifle.

This article was written under South African press restrictions that prohibit the reporting of nonofficial news of violence, unlawful gatherings, strikes, boycotts and other forms of organized dissent, or of any "subversive statement" as defined by the Pretoria government, unless cleared by a board of official censors.