JOHANNESBURG, SOUTH AFRICA, JULY 28 -- South African-led forces in Namibia reported today that they had killed 190 Angolan troops and Namibian insurgents in two major clashes in southern Angola.

Diplomats here said the incidents could represent the start of a sharp escalation in the prolonged confrontation between Pretoria and Luanda's Marxist government.

Military headquarters in Windhoek, the capital of South African-administered Namibia, said its forces had been pursuing about 120 insurgents of the South-West Africa People's Organization on Saturday when the insurgents and Angolan government troops ambushed them about 35 miles north of the Angolan-Namibian border.

After the first battle, the South African force continued pushing north into Angola, clashed a second time with Angolan troops and then continued the skirmishes before returning to Namibia Sunday. At least 190 were killed in the fighting, most of whom were believed to be Angolan soldiers, the headquarters spokesman said.

By the South African account, the battles were among the biggest that its forces have fought in recent years in southern Angola and apparently involved major Angolan units, perhaps two battalions.

South African officers believe that the large concentration of Namibian insurgents, members of a unit normally deployed well back from the frontier, was used to lure a fast-reaction task force into the ambush mounted by the heavily armed Angolan troops. Had the tactic succeeded, the Angolans would have inflicted scores of casualties in what might have been a considerable South African defeat, a senior officer said.

But the South African task force, outnumbered but drawn from a local, highly rated Namibian battalion, fought its way out of the ambush, according to Windhoek military sources. A barrage of rockets and grenades heavily damaged its vehicles, the sources said, but only one officer was slightly wounded. The South African task force then counterattacked and pursued the Angolans for more than a day.

Speculation arose here that the South African troops had actually gone to the assistance of its rightist allies, the National Union for the Total Independence of Angola, known by its Portuguese initials, UNITA, and that the fighting in Angola was about to escalate significantly.

Jonas Savimbi, the UNITA leader, has warned frequently in the past three months of a coming Angolan government offensive to be launched with Cuban and Soviet assistance against UNITA positions in southeast Angola in the present dry season. Savimbi, who also receives American arms, visited South Africa last month to make certain of Pretoria's support.

The scale and depth of South Africa's recent operations in Angola have suggested to some diplomats that they are intended to draw Angolan government forces out of the offensive against UNITA.

"Judging from what Pretoria has said and the number of casualties it claims to have inflicted, this was a major engagement that the South African forces pursued deliberately and rather vigorously," a western diplomat said in Cape Town. "They went far deeper into Angola than they normally do, they did not back away from {Angolan government} troops and they probably brought in reinforcements.

"The South African goal may have been to help Savimbi, either directly or by threatening an even greater incursion. The implication is that South Africa feels no political restraints on its cross-border operations into Angola and that it is prepared to do much more than before. We are not talking about an all-out invasion again, or even the resumed occupation of Angolan territory, . . . but we are looking at a considerable expansion of South African operations in Angola."

Angolan forces normally operate 30 miles or more back from the frontier with Namibia in order to prevent chance clashes with South Africa's routine cross-border patrols, which also have orders to avoid skirmishes with the Angolans.

Angola repeatedly has accused South African forces of operating deep inside its territory. It claimed earlier this week that eight South African battalions, totaling nearly 7,000 soldiers and supported by fighter-bombers and helicopter gunships, were across the border. About a quarter of the South African forces were deployed to support UNITA in southeastern Angola, according to Luanda, and the rest were operating in areas north of the central section of the border.

Military spokesmen in Windhoek and Pretoria acknowledge that South African forces based in Namibia regularly operate in southern Angola to prevent the infiltration of Namibia guerrillas and in pursuit of those slipping out of the territory back into Angola. But they dismiss as "exaggerated" the Angolan claims of such large-scale, cross-border deployments.