Physical and psychological torture of political detainees is used "systematically on a widespread basis" in South Africa, according to a report released today by the University of Cape Town.

The 2 1/2-year study, which included interviews with 176 former detainees, said 83 percent reported some form of physical torture by prison or police authorities while in custody, and almost the entire sample reported being subjected to psychological abuse.

Police did not respond today to a written request for comment on the study. In the past, police officials have strongly denied allegations of torture, although the government has made an undisclosed number of out-of-court financial settlements with former detainees or their families after lawsuits alleging physical abuse.

In 1982, Law and Order Minister Louis le Grange issued a set of directions on the humane treatment of prisoners that included a statement banning torture. But the report said le Grange's directions were "filled with provisos and escape clauses" and were not legally binding.

Nearly 2,700 persons have been detained under emergency regulations decreed by the government in July, and the report estimates that more than 300 others have been held under other statutes, including South Africa's sweeping Internal Security Act. Under that law, detainees can be held indefinitely without charge or access to lawyers or family.

Sixty persons have died while in detention since 1963, according to the Detainees' Parents Support Committee, an opposition human rights group here.

The report was compiled by two researchers for the Institute of Criminology at the university, considered one of South Africa's most prestigious.

Of those detainees who said they were tortured, 75 percent reported beatings, including punches, kicks and slaps as well as blows from a variety of implements. Fifty percent said they were forced to crouch or stand on their toes for prolonged periods, while 25 percent said they had been subjected to electric shock, and 18 percent to choking. Fourteen percent said their bodies had been suspended "in various forms."

The study said torture was most frequent among blacks, with 93 percent reporting some form of physical abuse. Nine of the 13 whites interviewed said they had undergone no physical torture. The most heavily tortured were those under age 20, according to the report.

It also accused authorities of widespread use of psychological torture, including false accusations (reported by 83 percent of the detainees interviewed), solitary confinement (79 percent), verbal abuse (71 percent) and threats of violence (64 percent).

The study also listed widespread health problems detainees said they suffered while imprisoned, including sleeping difficulties (reported by 60 percent), headaches (by 53 percent), weight and appetite loss, difficulties with concentration and nightmares. Many said these problems persisted after they were released.

The research sample was made up of 127 blacks, 36 persons of mixed-race or Asian origin and 13 whites. The average period of detention was three to four months and about half said they had been detained more than once.

Sixty percent said they had been harassed by police before their detention by methods such as threatening phone calls, wiretaps, or opening of mail and 68 percent characterized their arrest as violent, rough or aggressive.

Sixty percent said they had undergone six or more sessions of intensive interrogation, and nearly a fifth reported sessions longer than eight hours, most frequently by three or more interrogators.