As predictions swung first one way then the other about whether South Africa is about to free imprisoned black leader Nelson Mandela, his wife, Winnie, said today that she believes the government wants to release him but is hesitating, fearing the impact that he would have on the black-majority population.

She predicted that his release would trigger a mass popular response on the scale of Mohandas K. Gandhi's protests or the Ayatollah Ruhollah Khomeini's return to Tehran, which would swamp the streets and "bring the country to a standstill," but that, in her view, the government needed to free him to reduce international pressure.

Recent comments by government leaders, however, have given the impression that if Pretoria were to release Mandela, its chief purpose would be to "demythologize" him.

According to one scenario, if Mandela were to be released, there would be a brief and possibly dangerous period of mass excitement, but then the messianic image and international reputation that he has acquired through his long imprisonment would begin to fade when it became evident that he could not bring about any dramatic political transformation. As one senior government legislator put it in a recent conversation, "Then he will become just another black politician competing for support."

Most sources close to the situation, including Winnie Mandela, say the government has made a firm decision to release Mandela, who has served 24 years of a life sentence for plotting to overthrow white-minority rule, but predictions vary about when this is likely to happen.

Speaking in an interview, Winnie Mandela said that she had no doubts that the government had decided to release Mandela but that she felt it would be "a matter of months rather than weeks" before he is free.

"I imagine he might come out around midyear," she added, emphasizing that this was "just a feeling I have" and was not based on any direct communication with the authorities. She said the authorities had not spoken to her or her husband about his release recently.

Winnie Mandela also declared that her husband would refuse to leave South Africa as part of a prisoner exchange, which the government is known to be eager to negotiate, and that if released inside the country he would resume the leadership of the outlawed African National Congress, ignoring legal restrictions on it and confronting the government with the problem of whether to rearrest him.

Reports from Israel yesterday that South Africa wanted to "piggy-back" on Anatoly Scharansky's release and predicting that Mandela would be freed within the next day or two drew a denial from the government here.

Referring to a statement by President Pieter W. Botha two weeks ago that he might be prepared to negotiate for Mandela's release if the Soviets freed Scharansky and fellow dissident Andrei Sakharov and Angola returned a captured South African commando, Capt. Wynand du Toit, Justice Minister Jacobus Coetsee said in a statement last night: "Our conditions have not yet been met, and Mandela will therefore not be released."

Hopes that his release was imminent flared up again today when it was learned that Foreign Minister Roelof (Pik) Botha had flown to Geneva, prompting speculation that he had gone to see the International Red Cross, which has its headquarters there, about a prisoner exchange involving du Toit.

The Red Cross said last week that Angola had indicated an interest in exchanging du Toit for an undisclosed number of Angolan and Cuban soldiers held by South Africa. However, a Foreign Ministry spokesman said in Cape Town tonight that she knew of no plans for Foreign Minister Botha to meet with the International Red Cross in Geneva but that he had met there with Chester A. Crocker, U.S. assistant secretary of state for African affairs. Crocker is known to have been involved in recent discussions with the government in Pretoria about Mandela's release.

Tonight, the Johannesburg Star, South Africa's biggest daily newspaper, dampened the speculation again with a front-page report quoting unnamed senior government sources saying du Toit would have to be returned before Mandela's release could be considered but that this would not guarantee the release.

Winnie Mandela said a "change in the atmosphere" at Cape Town's Pollsmoor Prison, where her husband is held, was one of the indications she had that he might be freed. He was being exceptionally well treated and for the first time she was being given unlimited visiting rights, she said.

Winnie Mandela said that she believed the government is hesitating because it faced "a gigantic problem." On the one hand it realizes that releasing Mandela is necessary to ease international pressures and solve a financial crisis facing the country, while on the other hand it fears the implications of doing so.

"It is a Frankenstein monster of their own making," she said. "How do they release Mandela into an apartheid society knowing he will not abide by its rules? How do they release him while the ANC is still banned, knowing he will ignore the ban and take up where he left off as its leader?"

Above all, Winnie Mandela said, the government fears the impact her husband's release would have on the black population.

"The whole country will turn out to welcome him," she predicted. "The return of the people's Messiah. Everybody will be in the streets. Everything will come to a standstill -- and it will stay that way for as long as the people want it to," she said.