The leading South African financial newspaper, Business Day, quoted an unnamed senior figure in the ruling National Party today as saying that a Cabinet majority backed by President Pieter W. Botha was now in favor of releasing African National Congress leader Nelson Mandela from prison and that he could be free before Easter.

The report fueled expectations here that Botha's offer last Friday to free Mandela was more than a public-relations ploy.

Conversations with National Party members of Parliament and speeches by Cabinet ministers this week indicate, however, that if Mandela is released it will not be with a view to negotiating with him and his outlawed African nationalist movement about South Africa's future.

Instead, the white-minority government seems to be considering his release as part of a strategy aimed at neutralizing the ANC, while seeking to draw the more moderate Zulu leader, Chief Gatsha Buthelezi, into negotiations for a new constitution that would give the black majority a role in the running of the country for the first time.

A series of speeches by senior government members, including Defense Minister Magnus Malan, has denounced the ANC in even more vehement terms than usual. Today Malan also warned neighboring black countries in a speech in Parliament that South Africa might launch more cross-border raids if they did not accept an offer by Botha to join South Africa in establishing an organization to supervise regional security.

The spate of warnings and denunciations seemed designed to put the ANC beyond the pale as an organization to be negotiated with, and set the stage for an intensified counterinsurgency drive against it.

The idea of releasing Mandela, which the hawkish Malan is now said also to support, is being analyzed in this context.

The thinking appears to be that Mandela can be "demythologized" if he is released and then seen to be unable to bring about any dramatic political transformation, while Buthelezi is seen making progress in the negotiations.

After an initial period, during which his release might cause a surge of black expectations, his image would begin to fade and so help bring about the decline of the ANC, the thinking goes.

There are also fears of what would happen should Mandela, who is 67 and recently underwent surgery for the removal of his prostate gland, die in prison. Such a development could trigger large-scale rebellion and, in the words of one party sources, "give him eternal life." It is also felt that Mandela's release would make a major impact on opinion abroad.

Such a move could perhaps lead to a lifting of sanctions imposed by the Reagan administration last year and persuade international -- and particularly American -- banks to rescind their refusal to roll over $14 billion in short-term loans, which plunged the country into a financial crisis.

Party insiders say the government's main worry is that Mandela's release could set off a wave of political fervor in the black townships and restart the racial violence that is just beginning to subside after 17 months.

For this reason, party sources say, Mandela is unlikely to be released until the unrest dies down substantially.

The speculation follows Botha's announcement Friday that he was prepared to negotiate for Mandela's release on humanitarian grounds if the Soviet Union freed dissidents Anatoly Scharansky and Andrei Sakharov and Angola returned a South African soldier, Wynand du Toit, who was captured during a 1985 raid in that country.

Scharansky is believed to figure in a possible exchange of prisoners due to take place between East and West Berlin next week, and Angola said over the weekend that it is willing to exchange du Toit for an unspecified number of Angolans and a Cuban being held by South Africa.

Observers here believe Botha had inside knowledge of these negotiations when he made his statement, deliberately setting conditions he knew might be met.

They are suggesting he did this to overcome an obstruction to Mandela's release created last year when he declared that the ANC leader could not be freed unless he renounced his organization's commitment to guerrilla struggle. Mandela rejected this and Botha, fearing a backlash from white Afrikaners on his far right, seemed unwilling to retract it.

As progovernment Afrikaans newspapers noted prominently in their reports Saturday, Botha's new offer did not repeat his demand for a renunciation of violence.

At the same time, by making it appear that he had helped the West achieve the release of a Soviet dissident and by securing the return of a South African soldier, Botha could mollify right-wing criticism of a decision to release Mandela.