Cape Town — The ''bizarre'' detention of a young man in Cape Town in solitary confinement , a mysterious poisoning case, and the renewal of harsh restrictions on the wife of an imprisoned black political leader are all drawing increased public attention to South Africa's totalitarian ''security'' laws.
These let the police jail anybody for as long as they wish without trial or any access to legal aid, and allow for such other restrictions as including house arrest and ''banning.''
More than 140 people are believed to be in solitary confinement without trial under these laws at present, among them several trade unionists and some students.
Those who have been held have included the son of a Member of Parliament and even the niece of a cabinet minister.
Now detainees' relatives and friends are forming ''support groups'' to campaign for a better deal for detainees, as well as to comfort each other and to provide practical assistance where possible, especially to families suddenly left without a breadwinner because of an arrest.
One of the most recent to be released from solitary confinement is Mark Kaplan of Cape Town, who works at the University of Cape Town Community Video Resource Association.
He was told early in November that he could collect certain video tapes which had been seized by the police, if he called at the Central Security Police offices. Instead of giving him the tapes, which documented a protest meeting, and letting him go, the police arrested him.
Released just as suddenly a few days ago, Mr. Kaplan says, ''from the very first to the very last I continued to shout my innocence,'' but he was continually pressured to sign a statement. He refused. Finally he was released without signing the statement. ''The whole thing was bizarre from beginning to end,'' he said. ''I should never have been detained.''
Another detainee who has been freed - after five months - is Siphiwo Mtimkulu , a member of the Council of South African Students. He was held in Port Elizabeth, where the Black Consciousness leader, Steve Biko, who died in police custody after receiving brutal injuries, was interrogated.
After he was released, Mr. Mtimkulu complained of pains in his stomach and legs. After a while his hair fell out. He also became disoriented.
Finally, doctors at Cape Town's Groote Schuur Hospital diagnosed thallium poisoning, which one of them described as a ''homicide's dream poison.'' Thallium, once used as rat poison, was withdrawn some years ago because it was considered too dangerous.
It has not yet been established how Mr. Mtimkulu came to take the poison.
Then there is the case of Winnie Mandela, wife of the former African National Congress leader, Nelson Mandela, who is serving a life sentence on Robben Island , the country's main political prison.
Mrs. Mandela has been subjected to various bannings and orders limiting her movements and imposing other restrictions on her almost continuously for the past 20 years. When the latest expired, just after Christmas, she was summarily served with yet one more, imposing fresh restrictions on her that will last another five years.
One of South Africa's leading campaigners for civil rights, Helen Suzman, a founding member of the official opposition party in the all-white Parliament, the Progressive Federal Party, declared, ''Mrs. Mandela is being punished by purely arbitrary government action . . . which must disgust all people who believe in simple justice.''
Not surprisingly, members of the government are much more tolerant of the application of their security legislation.
One cabinet minister referred benignly to the detention without trial of the son of a Member of Parliament as providing the opportunity for him to ''cool off.''
Another minister objected to the term ''solitary confinement'' to describe the conditions under which some prisoners are held. It just so happened, he said , that they were detained in such a way that they were ''alone in a cell.''
And although it seemed at Christmas as if the police were relaxing slightly the conditions under which certain people were being held - even allowing some of them a short visit from a family member, some food and clean clothing - it seems more stringent restrictions are being applied again.
And when a police officer was asked why Mr. Kaplan, for example, was being denied the right to read his Hebrew Bible, he simply retorted: ''The less said about that the better.''