As all copywriters here must, Horace Mapanza sent his script for a television candy commercial to the South African Broadcasting Corp. for approval. He never thought the circus elephant in it would cause problems. But it did.

The Acceptance Department-- "We call it the 'rejection department,' " another advertising man said--of the government-run media monopoly told Mapanza he had to delete the elephant because the animal is sacred to the Venda people, a small tribe in the north. Also, they pointed out, the royal title of the wife of the king of neighboring Swaziland is "she-elephant." The ad might offend, they said.

Mapanza also knows he cannot use the words "toothpaste" or "potato chips" in his commercials because of the broadcasting corporation's insistence on "language purity." Since these words are not indigenous to the languages of Zulu, Xhosa or Sotho in which the commercials are being made, he has to say "slices of potato fried in oil" and "the soap that washes teeth."

Despite these idiosyncracies of making television commercials in South Africa, Mapanza and his colleagues are rushing to take advantage of the new opportunity opened to them by the launching on Jan. 1 of South Africa's second television station, aimed specificially at blacks.

The introduction of "black" television to complement "white" television, which has been broadcasting for five years in English and Afrikaans, is in line with the government's policy of keeping blacks and whites segregated in all spheres.

TV-2's air time will be equally divided among the major languages of South Africa's black population-- Zulu, Xhosa, Sotho and Tswana-- thus reflecting government policy of fostering linguistic and tribal differences among blacks that are used to justify Pretoria's policy of setting up separate, "independent" tribal "homelands."

Theunis Van Heerden, who heads TV-2, said there is no political basis for the new service. It is, he said in an interview, "a question of practicality. It's a question of catering to the people in their own languages. It's difficult to do that on one station. I don't see anything political in that."

Although they rarely see a black face on TV-1, blacks already own more than 236,000 television sets. For most city dwellers, language is not a problem. In the black township of Soweto outside Johannesburg, for example, 78 percent of the population speak English and 51 percent speak Afrikaans.

But on TV-2 a black anchorman will read the news and Pauline Khuzwayo will give cooking lessons in one of the tribal languages. There will be black actors in soap operas about boxers and the country-born innocent who goes to the big city, gets caught up with the wrong crowd and becomes a gangster.

These homegrown shows will be supplemented by imports. "The Jeffersons" will hold their family spats in Zulu, the "Incredible Hulk"--still neither black nor white, but green-- will be inflating in Xhosa and "Spiderman" will spin his webs in Sotho.

Not subject to the constraints of the religious mores of the Afrikaners, (who are not expected to watch it) TV-2 will be able to broadcast sports on Sunday, unlike TV-1.

The broadcasting corporation expects an initial viewership of 4 million in the main urban areas. Marketing surveys project that as electricity is brought to more black homes and as interest in TV-2 grows, 1.3 million sets will be sold to blacks and viewership will rise to 8 million by the end of 1982.

There is very little talk in officialdom of what impact TV-2 will have on South Africa in the long run, but Van Heerden believes it will give blacks "a window on the world, so to speak. If that will not change the people of this country, I don't know."

Both black and white television will be in color. The broadcasting corporation--whose nine-member policy-making board of directors is appointed by the government, although its revenue comes primarily from advertising and licenses--has not been stingy in setting up TV-2. Its equipment is regarded as the best money can buy.

Although blacks are employed as producers, the top officials of black television are white, which explains why many blacks are suspicious and skeptical of the new service.

Some say they fear that the white management, in a kind of "Amos 'n Andy" syndrome, will promote an image of blacks on TV-2 that fits whites' stereotyped ideas of blacks as shiftless, backward, rural, superstitious, violent and simplistic.

"I'm afraid they will wash our dirty linen on TV," said black television saleswoman Pauline Kato.

But most of their skepticism centers on TV-2's news and coverage of political events. Few blacks expect the black service to cover student boycotts, strikes, the war in Namibia, the eviction of black squatters, homeland leaders, and insurgents' bombings, to mention a few stories of 1981, with a black perspective.

This was the general drift of letters from black readers when a local newspaper asked them what they would like to see on black television.

"People like the Motlanas, the Bishop Tutus," who are black critics of the government, can be shown "debating on politics with the Thebehalis a black government supporter as long as what they want to convey shall not be censored. Although asking this is one hell of a hope," one reader wrote in.

Apart from politics, there were some interesting thoughts about what TV-2 should show. Many blacks said they preferred to see local blacks on the screen instead of "those who look American." One man urged that "many ignored sports like darts, checkers and chess" be screened on TV-2.

"I'm excited about it because even my children will now understand," said Doreen Mamashila. "It will change people's ideas. Old ladies, for example, will understand some of these advertisements like the one for self-rising flour--how do they know you are baking cake; they just see a cake in the oven. But now, if it is in Zulu, they will know."

The advertisements may tell much more about the broadcasting corporation's "apartheid of the air" than anything else. Under its guidelines, "if you're going to mix the races in an advertisement, it's got to be true to the South African way of life," said copywriter Mapanza. "It mustn't contradict what South Africans'--and I think they mean in this case, white South Africans'--idea of 'the South African way of life' is. But it's so difficult to know what is 'the South African way of life.' "

In practice, this means that if the races are mixed in a commercial, those made for a white station must have a majority of whites and those for the black one must have mostly blacks. For a while it was touch and go with the Acceptance Department for one of Mapanza's ads on a fast-food fried chicken outlet that showed a merry group of blacks and whites skipping along after a pied piper to get some chicken legs.

"This was seen as a suggestion that all those people were at one gigantic integrated picnic," Mapanza explained.

Then there are the problems perhaps unique to South Africa. One cookie commercial showed young white schoolboys sitting on their beds in a large dormitory at a boarding school. When it came to shooting for the black equivalent, the crew took that scene outdoors because they feared the dormitory interior would send the wrong message.

For people so used to jailings, blacks might have thought, "Ah shame, the poor fellow has been detained," said Mapanza.

Television saleswoman Kota tells of the little old lady who came to buy a television set because "she thought she would see her granny from Rustenberg on it." Admitting that she did not disabuse her customer of this notion until after she had bought the set, Kota explained: "She thought that if she could see someone from Washington, she could surely see her granny from Rustenberg. And you never know, by chance, some day she may."