Thousands of Afrikaners, despite their puritanical Calvinist religion, chuckled with delight at the sexual antics of a television crew and its groupies, including two british aristocrats, Lord Seldom and Lord Sudden, and two South African beauty queens, Miss Transvaal and Miss Orange Free State, in the Afrikaans novel of Etienne Leroux, "Magersfontein, O Magersfontein."

Then suddenly, after the book had sold 4,000 copies, won critical acclaim and a top national literary award over the course of a year, the South African government's censorship board banned the novel last November on the ground that even though the "average man" probably won't read the book, it would offend him if he did.

The banning of the book, which even the censorship board admitted was of "high literary value," set off a furor among Afrikaner intellectuals. The editorial pages of the Afrikaans press (as well as the English) were ablaze with indignation. Leroux was called "South Africa's Solzhenitsyn" and, for the first time since the present censorship structure was set up in 1974, publishers are challenging a book banning in South Africa's higest court.

The replacement of the former minister of the interior, Connie Mulder, in a recent cabinet reshuffle came none too soon for a frikaner writers. They are pinning their hopes for relief from censorship on his sucess, Alwyn Sshlebusch, who has promised to read "Magerfontein, O Magersfontein" as "a matter of urgency."

The government's censorship organization, which is responsible for monitoring both pornographic and politically undersirable works, functions under legislation which eliminated the right of authors to appeal a banning to the supreme court. The court can only review a banning to see if it was done "in bad faith", it cannot revoke it.

Writers and publishers complain that the censorship is becoming tighter. The higest censorship body, the Publications Appeals Board, acknowledge in a report to parliament last month that it had banned considerably more works in 1977 than in 1976. The number of banned "subversive" publications rose 40 per cent and those that were deemed "offensive or harmful to public morals" rose by 49 per cent.

Among the subversive documents banned in 1977 was "Detention Without Trial in South Africa, 1976-77" by the highly respected South African Institute of Race Relations. The report described that various security laws that permit a person to be held by police without being charged and listed people who died in police detention.

Books, films, T-shirts and posters which get banned are listed in the newspaper periodically. Recent lists have included "How To Grow Marijuana Indoors and Under Light," "How to Avoid Electronic Eavesdropping," a T-shirt with the slogan, "We the People," and "Roots of a Revolution" by the Rev. Ndabaningi Sithole, who is negotiating Rhodesia's transition to black rule with Prime Minister Ian Smith.

But Joh Pretorius, director of publications at the government's censorship department, denies censorship is becoming tougher and said, "Since 1963 not more than 25 Afrikans books have been banned."

Like all books that are published in South Africa, "Magersfontein, O Magersfontein" was reviewed by one of the 30 local censorship committees that are set up all over the country. Leroux's skill in contrasting the decadent 1970s lifestyle of the television crew, filming a reenactment of the Boer War battle of Magersfontein, with the heroic stature of those who had fought in the historic 1899 engagement, gave the book recognized literary merit, so the committee let it be circulated.

But at a National Party congress in the Orange Free State, Connie Mulder was asked by a 28-year-old woman why the book was not banned. Pretorius said the minister also received many letters complaining about filthy language, blasphemy and references to sex in the book.

As a result, Mulder reffered the book to the 10-man, government-appointed Publications Appeals Board to review the lower committee's ruling. Pretorious estimated that out of about 20 works sent by Mulder to the board, only "three or four" were not banned.

The board ruled that "the average man . . . cannot understand why just these filthy words should appear in the book and with such frequency . . . and . . . just for the very reason that he does not understand tha book, the average man will be constantly irritated by the unsavory language with the result that the cumulative effect on him will be one of repugnance."

The idea "of banning a book of people who won't read it is preposterous." said Leroux's publisher, Koos Human. His company has asked the South African supreme court to rule if the views of the "average man" rather than those of the likely probable reader" were the correct grounds for the board's ruling.

Leroux, a member of a respected Afrikaner family that also produced a former National Party cabinet minister, finds some irony in the battle over his novel. The 1899 battle was "a comedy of errors," he says, "and ironically, what's happened to my book is the same thing."

Leroux is one of the Sestigers - a group of young Afrikaner writers who broke away from the mainstream of Afrikaans literature in the 1960s to begin writing about taboo subjects like sex.

Four of his 11 "symbolic novels" have been published in English, the best known being "Seven Days at the Silbersteins." Leroux counts authors Graham Greene and Paul Theroux among his "best friends."

"I was sad [about the bannings], you bloody well believe it, to realize that book is now gone, dead," said the 55-year-old Leroux, who works a sheep and vegetable farm in the Orange Free State by day and writes by night. "Now I've got to worry about overreacting in my next book and, for example, saying, "Well, I'll Bloody well show you," or underreacting - that's wrong, too.

"One thing is for sure, I'm not going to write with a bloody textbook [on censorship] next to me."