Like a pot boiling over, South Africa's racial unrest has again spilled across its borders and claimed new victims with yesterday's commando raids on rebel targets in Botswana, Zambia and here.

The South African bombs that tore through a suburban house and an office in this capital city yesterday morning have likewise shattered the fragile understanding between the white-ruled regional superpower and its strongest black neighbor.

The violence marked South Africa's first open attack against Zimbabwe and its first raid near the Zambian capital of Lusaka.

The raids, in which two civilians were killed and about 15 wounded, are certain to force the six black "front-line" states neighboring South Africa into a search for new sources of military support, according to western diplomats and other analysts. One result, they said, is that these governments may turn to the Soviet Bloc for further help, something that many of them, especially Zimbabwe, have tried to avoid.

For South Africa, the raids mark a new triumph for those who advocate an "iron fist" policy in the region. They come at a time when civil violence inside the country, nearly two years old, shows no sign of abating and the government is seeking to stave off defections among its most hard-line backers.

Although the damage inflicted on South African rebels appeared slight, the message that was delivered to all concerned -- to the insurgents, the black states, western governments and, perhaps most importantly, Pretoria's conservative white constituency -- was that South Africa still has a virtual monopoly on military power in the region and will use that power regardless of international consequences.

Since their country's birth six years ago, Zimbabwe's black leaders have striven hard to maintain a quiet understanding with Pretoria. No government in the region had better succeeded at keeping its territory off-limits to the rebel African National Congress, the main South African resistance movement.

Military and police officials here -- including Zimbabwe's state security minister -- held regular secret meetings with their South African counterparts at which security information was discussed and shared. The latest meeting, now cancelled, had been scheduled to take place here today.

The gentlemen's agreement began to unravel last December when South Africa charged that land mines in the border region of northern Transvaal had been laid by ANC operatives crossing over from Zimbabwe. Pretoria threatened to strike, but after security officials met, the matter seemed defused.

Now the delicate truce has been destroyed and the government of Zimbabwean Prime Minister Robert Mugabe publicly humiliated. The raids have also appeared to vindicate the views of hard-liners here who have long argued that Zimbabwe, which considers itself socialist but nonaligned, should seek Soviet weapons and military advisers to prepare for a long siege by Pretoria.

Soviet defense officials visited Harare earlier this year as part of a trade delegation and Zimbabwe is weighing whether to purchase a Soviet air defense system, MiG jet fighters and other weaponry, according to diplomatic sources here.

"The Zimbabweans thought they had a workable relationship with the South Africans, especially on the security side," said a senior western diplomat here. "To have that literally blow up in their faces has got to give them pause."

Zimbabwe's 40,000-member Army is one of black Africa's best-trained and its intelligence network is extensive. Officials here had long predicted that should South Africa attack, its commandos would not escape unbloodied.

Nonetheless, the raids here were successfully completed within yards of two police stations, virtually under the noses of the authorities.

Zimbabwean investigators believe the raiders entered the country via a private plane by posing as tourists, reliable sources said. They reportedly landed near the Hwanne game reserve in western Zimbabwe, rented cars and drove to Harare.

At least one was said to have spoken warnings to bystanders in Shona, the native tongue of the country's ethnic majority, setting off speculation that the raiders included former members of the Selous Scouts, an elite commando unit disbanded in 1980 when blacks came to power here in the former Rhodesia.

Government officials refused to divulge how the raiders escaped or whether some are still at large inside Zimbabwe, or to reveal any information about the four suspects Mugabe said were arrested yesterday.

Most countries would consider such a cross-border attack an act of war. Yet Mugabe, while condemning the attack and repeating previous calls for international sanctions against Pretoria, spoke cautiously yesterday.

It was a tacit admission that there was little else he can do. His Army is considered no match for the 80,000-man South African Defense Force, southern Africa's most highly rated force.

Mugabe also ruled out, for now, symbolic gestures such as suspending commercial flights to Johannesburg or closing the small South African trade mission here. Such moves would invite economic retaliation by South Africa, through whose ports, roads and railways more than 80 percent of Zimbabwe's foreign trade flows.

Besides pushing Zimbabwe further to the East, the raids also are likely to feed repressive tendencies that are a prominent feature of political life here. Some observers fear that the government's tendency to characterize political opponents as "enemies," its use of detention without trial and other emergency powers and the frequency of human rights abuses such as police torture of detainees are all likely to increase because of heightened fears of South Africa.

The raid has all but killed hopes that western diplomatic initiatives, whether by the Eminent Persons' Group of the Commonwealth nations or by the United States, can reduce regional violence or start a process of negotiation between Pretoria and the ANC.

Analysts in South Africa suggested that the government had opted for a display of toughness to impress white voters increasingly disenchanted with the government's inability to stop black unrest. Pretoria also sought to stem the view that it is caving in to western demands for concessions to the country's disenfranchised black majority, they said.

A neo-Nazi movement called the Afrikaner Resistance Movement, which was regarded as little more than a fringe group a year ago, recently drew a crowd of 6,000 at a rally in the Pretoria city hall. And the government's information chief, Louis Nel, was forced to abandon a recent meeting when rowdy right-wingers shouted him down at a party rally east of Pretoria.

Analysts said South African President Pieter W. Botha is reasonably confident that despite western condemnation of the raids, the countries that are economically most important to Pretoria will be unwilling to go along with mandatory sanctions.