The two-month-old strike of high school students in this sprawling African township has suddenly spread to include primary school children in what appears to be a silent portest against the government's decision Wednesday to ban virtually all black opposition groups and detain more than 40 of their leaders.

It was not immediately clear how many of the 142,000 Africans attending primary schools had joined the boycott, but a large number of them were reported by various sources to have stayed away from classes yesterday and today.

In the first such move against Asians, police today detained 97 Indians in Johannesburg's Asian suburb of Lenasia after they attempted to hold a prohibited public meeting at lunchtime.

Meanwhile, there were indications today that the South African government may be planning to take action to close the small United States Information Service's branch library here.

Two white South Africans posing as businessmen and saying they wanted to give books and money visited the American reading room today and carefully noted materials availabe on the shelves of the cubbyhole-size center located on the second floor of the YMCA building in the East Orlando district of the township.

The tow men said they were representatives of the Anglo-American Corp., but a check with the company later indicated this was apparently not true. It was generally assumed here that they were South African security agents sent ot investigate the center.

It was the second time that the two-year-old reading romm has been visited recently by mysterious white South Afticans posing as businessman and offering to make a donation of books and money.

It is already well known here that South African authorities are less than happy with the USIS outpost, which serves at times as a meeting point for young black Soweto militants. For example, the Medupe Writer's Association. One of the 17 black organizations outlawed Wednesday, held some of its redings there.

In the sprawling township of Soweto, which is home for 1.2 million Africans working in Johannesburg, all 27,000 students in the state-run secondayr schools have been out on strike for several months. They were joined recently by about 380 of their 750 teachers.

A spokesman for the Department of Bant (African) Education admitted today that the boycott is spreading and said primary school children are being "threatened by people who call themselves students" telling them "out or you have had it."

There have been several reports in the local press recently of students breaking into the primanry schools here and elsewhere to disrupt classes and force the pupils to join the strike. In some cases, there has been violence including stone throwing.

In another development today, the new South African administrator-genral of Namibia (Southwest Africa). Justice M.T. Steyn, announced the repeal of the pass laws in the territory in preparation for elections and its independence something next year.

The pass laws, which tightly control and restrict the movement of Africans are detedted by all blacks both in Namibia and here in South Africa. There have been many calls from abroad for their abolition, icluding most recently from some U.S. government officials who have suggested such a step would be a good indication of South Africa's earnest intention to make meaningful changes in its system of apartheid, or strict racial segregation.

While showing no signs of introducing similar legislation here, the South African government has now moved in Namibia to abolish the pass laws, the Immorality Act and the so-called Mixed Marriages Act prohibiting sexual relations or marriages between the races.