South African and Cuban troops have clashed in the Namibian-Angolan border war for the first time in nearly seven years, according to South Africa, which claimed it killed one Cuban and captured another.

Brig. Gen. Jan Klopper, acting commander of South African forces in Namibia, issued a terse statement today reporting the encounter. He said the Cubans had "interfered with" South African and Namibian troops engaged in a "follow-up operation" against insurgents of the South-West Africa People's Organization, which is fighting for Namibia's independence from South Africa.

Defense headquarters in Pretoria declined to add anything to the statement. It would not say where or when the clash took place, or where the captured Cuban was being held.

Klopper's statement indicated that the encounter had probably been inside Angola, although he only referred to "the operational area straddling the border." South African troops often penetrate deep into Angola in what are officially termed "hot pursuit" or "follow-up" operations against SWAPO.

Between 10,000 and 20,000 Cuban troops are in Angola, where they tipped the balance in favor of the ruling faction in the Angolan civil war.

The clash was the first between South African and Cuban troops since South African forces invaded Angola in mid-1975 and reached the outskirts of the capital of Luanda, 700 miles north of the Namibian border.

At that time South Africa captured three Cubans, and several South Africans were taken prisoner. Later an exchange was arranged through the Red Cross.

Since then, according to the South Africans, the Cubans have always kept clear of the "hot pursuit" forces.

Last August, a Soviet officer and a Russian woman were killed in Angola during a major South African incursion, and another Russian officer was captured. They were apparently part of a group of military advisers.