Black high school students in South Africa's segregated townships continued their boycott of classes today but primary school pupils went to the first day of post-holiday classes in increasing numbers.

Officials in Soweto, the black township south of Johannesburg, said high school attendance remained low as most students in the higher grades appeared to be continuing the six-month boycott.

Blacks protesting the requirement that Afrikaans, the language of the ruling white minority, be taught and used in school led to antigovernment rioting in the township last June and the subsequent boycott. The government since has said that both English and Afrikaans could be used in the classroom.

Police patrolled three Cape Town townships, Langa, Nyanga and Guguletu, to prevent intimidation of returning students by black militants trying to keep them away from school, security officials said.

Last week the government announced new programs to improve nonwhite education: free text books for senior high school pupils in 1977 and for all students in 1978, government school maintenance and construction, upgrading of black teachers through adult education centers and grants for university study and parental choice of school councils.

These other southern Africa developments were reported:

British diplomat Ivor Richard said in Gaborone he may have won the approval of Botswana's president for what would be designed as a steadying British presence in Rhodesia during the transition to black majority rule. This was the first visible progress made by Richard, Chairman of the Geneva conference on Rhodesia, during his southern Africa shuttle, aimed at ending the conference stalemate. Richard left Botswana late today for Mozambique.

Presidents of the "front-line" group of southern African countries - Zambia, Botswana, Tanzania, Angola and Mozambique - will hold a summit meeting in Lusaka, Zambia, at the end of this week to decide what role they want Britain to play in Rhodesia during a transition to majority rule, a reliable source in Lusaka said.

A stream o fordinary black, Angolan civilians who are not refugees from fighting in their country now are crossing the border to seek food and medical treatment from South African authorities in Southwest Africa (Namibia) a senior administration official said in Windhoek.

South African journalist Eric Abraham, 22, declared a banned person and placed under house arrest in Cape Town last November, arrived in Botswana after escaping across the border.