JOHANNESBURG, NOV. 2 -- The South African military command reported today that its forces in Namibia had crossed into southern Angola and, in a major "preemptive strike," had killed more than 150 guerrillas of the South-West Africa People's Organization (SWAPO).

Military headquarters in Pretoria said that 11 members of the attacking force, including nine white soldiers of the South African Defense Force and two from the predominantly black South-West Africa Territory Force, were killed during the incursion Saturday.

It was the largest South African Army land operation inside Angola since July 25, when an infantry unit pursuing SWAPO guerrillas about 35 miles north of the border was ambushed by Angolan troops. At least 190 were killed in the fighting, most of them believed to be Angolan soldiers.

South African troops were reported to be inside Angola last month supporting anticommunist rebels of Jonas Savimbi's Union for the Total Independence of Angola in clashes with Angolan government troops.

A military command spokesman said Saturday's operation was aimed at "SWAPO elements preparing for their seasonal infiltration of South-West Africa {Namibia} and ensuing terrorist activities against the inhabitants."

SWAPO has made cross-border attacks in past rainy seasons as a means of covering their tracks.

Military officials said the attack hit a SWAPO base in Angola's Cunene Province -- adjacent to the 220-mile-wide Ovamboland tribal territory in north-central Namibia -- where SWAPO maintains training bases in conjunction with Angolan troops.

The 11 South African dead announced by Pretoria was a high figure for a single engagement.

The Army command does not normally disclose cumulative casualty figures, but last year's total of announced deaths in the Angolan "operational area" was about 60.

In the 21 years in which South African forces have been fighting the bush war with SWAPO, more than 10,600 SWAPO fighters have been listed as killed, with the unofficial security forces' death toll at between 600 and 700.

In 1980, at the height of the war, SWAPO combat units of more than 200 guerrillas each crossed the porous border to conduct sustained operations inside Namibia.

Today, the South African Army estimates that only about 60 guerrillas are inside Namibia at any given time, and that they rarely stay for more than two or three days.

This year, nearly 800 SWAPO guerrillas attempting either to enter or leave Namibia have been killed, according to South African military intelligence officers, compared to 694 last year.

Military sources in Namibia say that because of the almost daily cross-border pressure, SWAPO has been forced to move its main headquarters and training bases nearly 200 miles north of the border.

South Africa has administered mineral-rich Namibia since capturing the former German colony during World War I.

It has refused to accept a 1978 United Nations independence plan unless Cuba agrees to withdraw an estimated 27,000 troops in Angola.