South Africa today issued a stern warning against domestic terrorism after police commandos crushed a guerrilla takeover of a bank that left the nation's ruling white minority wondering whether the fight against apartheid is entering a new, violent phase.

Commandos of the police antiterrorist brigade blasted their way into a suburban Pretoria bank Friday, killing three black nationalist who had taken 25 persons hostage in a raid to demand the relase of imprisoned black leaders.

One of the hostages, a 19-year-old bank teller, was killed in the shootout and a second died early today. Three others hostages remained in critical condition. It was the first time black guerrillas had taken hostages to press their fight against South Africa's white rulers.

The antiapartheid Rand Daily Mail, in a front-page editorial this morning, condemned the bank takeover, but appealed to the government to forge ahead with racial reforms before the country faced "terrorist war."

Some of the hostages said today that the guerrillas told them they had trained in Angola. Peter Bierman, a teller at the Volkskas Bank where the siege occurred, quoted the guerrillas as saying they "were fighting for equal rights and they wanted to live as people lived in Cuba and Russia."

Prime Minister Pieter Botha said, "Any form of terrorism or any act going against the laws of the country will have the state to contend with."

Meanwhile, a black naitonalist leader in Zambia said the bloody bank siege was the start of a guerrilla war against South Africa.

A spokesman for the outlawed African National Congress, to which the gunmen reportedly said they belonged, said, "South Africans can expect a steady escalation in urban guerrilla attacks of all kinds. Militants will not be frightened by the episode."