Strikes, school boycotts and violence in black areas are giving South Africa its most serious period of unrest in 2 1/2 years.

The situation is still far from the chaos that gripped the country during widespread upheavals in 1976, but the recent incidents show that anger and discontent, especially among young blacks, are still serious.

Many observers say that the troubles during the past two weeks may foreshadow what the 1980s will bring to this racially divided country -- growing militancy among black workers that disrupts the economy and recurring protests by students and other youths who cannot find jobs.

The election victory of former guerrilla chief Robert Mugabe in neighboring Zimbabwe profoundly affected the consciousness of blacks and contributed to the mood behind the current unrest.

Also, a date that touches emotional chords in blacks is approaching. June 16 is the fourth anniversary of the violent clash between police and demonstrating students in Soweto. The protest ignited 18 months of unrest that culminated in a massive security crackdown on black organizations and leaders in October 1977.

Recent events appear to be bringing to an end a period of grace that Prime Minister Pieter Botha has enjoyed by his talk of reform. Disillusionment is setting in as blacks see these promises failing to bring tangible change to their everyday lives.

In addition, Botha's most crucial reformist political initiative has fallen far short of what observers say is needed to defuse the black-white tension here and renew the trust between them. A "president's council" that is to work out a new constitution will not include black members.

One of the most striking aspects of the recent unrest has been the anger and violence that youths have vented on other blacks -- especially those who occupy posts in the white-dominated political structure -- who tried to discourage their protests.

In the grimly industrial town of Port Elizabeth, for example, boycotting students attacked and stoned to death a black man who tried to persuade them to return to school.

By far the most serious violence occurred in the black townships near Bloemfontein, a center of white conservatism. Boycotting students stoned cars, set fires and erected roadblocks for two days in their townships. Police opened fire at one point, but denied responsibility for a man later found dead.

A white soldier taking blacks from work to home in one of Bloemfontein's black townships was attacked by a group of blacks, who beat him unconscious. Then, in an example of the contradictions in black-white relations here, another group of blacks took the assaulted soldier to a police station.

The most unusual protest so far came Saturday when thousands of Colored (mixed race) students protesting "inferior education" marched into crowded shopping centers in Cape Town. They jumped on counters, blocked lines of shoppers with carts of goods and sang freedom songs.

Police eventually charged the largest group of about 3,000 and arrested 105 students.

Police said the students were "looting" the stores. Students said the aim of their action was to call attention to their parents' "consumer power" and to the "exploitative" economic system in South Africa.