South African jet fighters launched an air attack against the capital of neighboring Mozambique today in quick retaliation for Friday's bombing in downtown Pretoria by black nationalists. Six people were reported killed and 40 wounded in the air attack.

The Defense Ministry said seven locally made Impala jets rocketed and machine-gunned six houses and a nearby antiaircraft-missile site in Maputo. The ministry spokesman charged that the houses were all "terrorist camps" of the African National Congress, the opposition organization seeking to overturn white minority rule in South Africa.

In Maputo, the official Mozambique news agency AIM, however, said the raid on the suburb of Matola hit private dwellings and a jam factory. The dead included two Mozambican women and two children, and one of two men killed was reportedly a South African refugee.

The African National Congress issued a statement from its exile headquarters in Lusaka, Zambia, denying that it had military installations anywhere in Mozambique.

The ANC, which had earlier limited itself to an expression of approval of Friday's bombing, issued a statement from offices in Dar es Salaam, Tanzania, directly claiming responsibility for the rush-hour blast in Pretoria that killed 18 people and wounded 217, Agence France-Presse reported.

The ANC bombing and South African reprisal represented a major escalation on both sides in the struggle between the militarily powerful South African government and its black opponents, and western diplomats expressed concern that the incidents may be the beginning of a cycle of violence that could transform the region into a focus of increased international tension.

Until now the ANC followed a policy of avoiding civilian targets. Friday's bomb, while planted outside Air Force headquarters, exploded in a busy street during the afternoon rush hour, making civilian casualties virtually inevitable.

For South Africa, today's air raid was the first time the government has used the Air Force in a cross-border attack against suspected black nationalist havens. In recent years, South Africa has launched raids by commando squads into neighboring countries, as it did in 1981 against African National Congress offices in Matola, the target of today's air attack.

An Associated Press reporter visited the scene of the attack and said he saw the bodies of two men and a woman in the jam factory. He said he counted 11 wounded in the surrounding area, including two children.

The Mozambican news service said congress members who had lived in Matola had left after South African commandos raided the suburb in 1981, killing 13 people.

A Reuter reporter on the scene said he found no signs of a missile site in the attack area.

Announcing the raid early today, Defense Minister Magnus Malan emphasized its retaliatory nature and threatened to attack the ANC in other countries as well. "Although the retaliatory attack can never compensate for the cowardly car bomb attack in a busy central area of Pretoria, it will at least demonstrate to the world and to South Africa's enemies that we are ready to act where and when necessary," Malan said.

Speaking later in the South African Parliament in Cape Town, Malan added: "The world and our enemies must see this only as an example of our capabilities and what we are prepared to do to protect our territorial integrity and the letting of innocent blood."

He repeated a warning that South Africa would not hesitate to launch attacks into any country believed to harbor congress insurgents.

Some observers said they thought the congress might now seek vengeance for the Mozambique raid by striking again at civilian targets inside South Africa, thus continuing the cycle of violence.

What is worrying western diplomats even more is the possibility that some black "front-line states," increasingly anxious at the South African actions, may turn to Communist countries for military reinforcement--as Angola appealed to Cuba for aid against South African incursions.

The entry of Soviet-aligned states, the westerners fear, would lead to even more aggressive retaliation by South Africa.

Diplomats in Lesotho and Botswana, two neighboring countries that accept congress refugees from South Africa, said in telephone interviews that the level of anxiety there had risen sharply as a result of the Mozambique raid and Malan warning.

John Barratt, director of the South African Institute of International Affairs, said in an interview here he thought there was a serious danger of the escalating violence resulting in foreign troops being introduced into the region. "The real danger I foresee is that as the Southern African conflict escalates it is going to become increasingly internationalized," he said.

At a press briefing in Pretoria today after the air raid, the chief spokesman for the defense force, Brigadier Kobus Bosman, said the plan had been drawn up as a contigency, a long time ago. "We had intended making the attack on Saturday, but the weather was bad," Bosman said.

Bosman played a tape recording that he said was of a conversation between the leader of the Impala formation and the control tower at Maputo airport as the jets neared the target area.

"I have an important message for you," the voice on the tape said. "Tell your military headquarters that aircraft are conducting operations against the ANC. We have no quarrel with the Frelimo Mozambique government, and any interference against these aircraft will result in immediate retaliation."