South African troops attacked guerrilla positions in Zambia, killing at least 16 Nambibian nationalist guerillas in retaliation for an attack on Namibia (Southwest Africa), South African military authorities said yesterday.

The retaliatorry attack Wednesday immediately followed the two-hour bombardment by guerillas of the Southwest Africa Peoples Organization of two towns in Namibia in which nine South African troops were killed and 11 were wounded. (SUBSECTION) ambia said 12 civilians had been killed and 16 wounded in a South African attack on the Zambian border town of Shesheke and charged South Africa with bombing a school.

Gen. Jan Geldenhuys, South African commander in Nambia, said it was possible that Zambian defense forces had been hit in the raid but a spokesman in Pretoria denied the school had been attacked.

Zambia charged that the fighting was still going on, but a South African military spokesman indicated that it had ended.

South Africa meanwhile backed off from the charges made Wednesday by military authorities that Zambian regular troops assisted SWAPO in its bombardment of Katima Mulilo and nearby Wenela in northestern Namibia.

Zambia denied Wednesday that its troops had been involved in the two-hour bombardment. Observers here speculated that local Zambian troops in the area of the fighting might have been drawn into the exchange without the knowledge of their superiors,

"There are indications that it may be possible that the Zambian government was not officially involved in the latest incident," Prime Minister John Vorster said.

Vorster yesterday called on Zambia to restrain SWAPO from further attacks in Namibia, where South Africa has agreed to a cease-fire under a U.N. plan calling for elections and independence by the end of the year, but SWAPO has reejected truce conditions until the plan takes effect.

Voster warned Zambia that it "has no other option but to act in such a way in the future that such acts cannot easily be repeated.

"A responsibility also rests upon those countries which make their territory available to SWAPO for its operations," he said.

Zambia has allowed SWAPO to use its territory for bases, although most SWAPO operations have been conducted from southern Angola.

Although public opinion among white South Africans has been aroused by Wednesday's bombardment, which resulted in the highest South African casualty figure for any single incident so far in the Namibian war, observers here do not believe the latest clash will set back the peace plan unless either side launches an other attack.

U.N. representative Martti Ahtisaari left Namibia Wednesday for U.N. headquarters in New York, just before the fighting broke out, with his suggestions for for implementing the plan.

"The real question is, will there be anything else," said an official closely involved with the plan. "If this is the full extent of South African retaliation, it won't put Zambia or SWAPO off the track in regard to the proposals."

South Africa is known to have launched minor raids into Zambia previously to strike at SWAPO camps, in addition to the much publicied raid into southern Angola May 4 in which as many as 1,200 people are believed to have been killed at what Pretoria said was a SWAPO training camp.