More than 750 persons have died in political unrest in South Africa since violence broke out in the black townships of the Vaal Triangle south of Johannesburg on Sept. 3, 1984, according to figures compiled by the South African Institute of Race Relations and an update Saturday.

As of Oct. 7, the institute's death count stood at 744, and at least 13 more persons have been reported killed since then. Institute researchers agree with government estimates that about two-thirds of the deaths result from police action, while the rest of the victims were killed by fellow blacks. Five whites and 14 black policemen have been among the victims.

These are official statistics, based on bodies counted on the scene by police, or recorded at local hospitals and mortuaries. Many blacks contend that the actual number of deaths is higher. Anglican Bishop Desmond Tutu commonly cites 1,000, although he offers no explanation for the figure.

As of Friday, police had reported arresting 4,960 persons under the emergency regulations, 1,006 of whom are still being held. The figures do not include more than 1,500 schoolchildren rounded up in Soweto at various times and released after one to three days for allegedly violating the emergency ban on school boycotts. Nor does it include the 441 persons who the Detainees' Parents Support Committee says are being held under other security laws.