ULUNDI, SOUTH AFRICA, JULY 14 -- Zulu Chief Mangosuthu Buthelezi formally converted his Inkatha organization, a black liberation movement, into a political party today, inviting whites and other races to join it in building "the great new race-free South African democracy."

Buthelezi's speech at Inkatha's annual convention in this capital of the nominally self-governing Kwazulu homeland highlighted the shifting sands of today's South African politics. Various white and black parties are now jockeying for position as this country begins moving away from white-minority rule toward what many hope will be a new non-racial democratic system likely dominated by the African National Congress.

Buthelezi's bid to turn the Zulu-based Inkatha into a multi-racial party was a direct challenge to his rivals in the ANC, which has been trying to isolate Buthelezi and destroy him politically. Buthelezi made a strong appeal to whites, Indians and mixed-race Coloreds to join his new Inkatha Freedom Party to help block what he called "the ANC's attempts to monopolize political power to produce a bipolar South African situation in which it alone can deal with the South African government."

He said that "no power on earth and most certainly nothing the ANC can do" would stop a new Inkatha party from claiming "its rightful place at the negotiating table" in future talks between the government and its black opposition on a new constitution.

"Inkatha warns the ANC that the pursuit of winner-takes-all politics is dangerous in the extreme," he said.

Buthelezi sought to draw a sharp contrast between the ANC, which he described as "a violent organization" still committed to the armed struggle, sanctions and nationalization of key sectors of the economy, and his Inkatha Freedom Party, which he said stands for non-violence, an end to sanctions and an economy driven by free enterprise.

He said Inkatha's Zulu-dominated membership would be "great company for whites" because his black supporters would prove "reliable partners" in pursuit of a new democracy in South Africa and stand by the whites "when the going gets tough."

"Inkatha has been the premier nonviolent, pro-democracy black political organization of the country," he told the 10,000 delegates and observers attending the convention, held in several huge tents here.

"It now aims to become the premier nonviolent, pro-democracy political party of the new South Africa. We can do it. We can put a non-racial democratic Inkatha together in such a way that it will become a powerful force in the land," he added.

The ANC adopted a policy of multi-racialism in its 1955 declaration of principles called the Freedom Charter.

The old Inkatha, which claimed 1.7 million members, had the reputation of being mainly a Zulu organization, largely because its stronghold is in Kwazulu and Buthelezi is a Zulu prince and chief minister of the homeland.

While currently the second largest black political organization after the ANC, it has failed to gain wide support among non-Zulus and is increasingly being challenged by the ANC even on its home turf.

Because of Buthelezi's opposition to sanctions and the armed struggle, ANC supporters have considered him a government puppet. They blame him for the violence in Natal, the eastern province that includes the Kwazulu homeland. More than 3,000 people have died in Natal during the past three years in fighting between Inkatha and the ANC's Zulu supporters.

It remains to be seen whether Buthelezi's bid for white support and a major place in the new South Africa will succeed. Buthelezi has hired a well-known British political public relations expert, David J. Kingsley, to help forge a new image for Inkatha with whites and non-Zulu blacks and to raise money abroad for its new political endeavor.

Some South African political commentators predict that Buthelezi's Inkatha will become a victim of the transition from the old to a new South Africa, together with the white opposition Democratic Party, whose liberal policies have largely been taken over by the ruling National Party of President Frederik W. de Klerk.

One of the leaders of the Democrats, Wynand Malan, announced Wednesday that he will resign his party post and his seat in parliament, saying, "What I have been working toward is now becoming a reality."

Inkatha "can try to reform itself within this new political arena that has been created -- in other words, go for white membership," said Frederik van Zyl Slabbert, head of the Institute for a Democratic Alternative. But "if de Klerk goes non-racial, what is the difference between the Inkatha philosophy and the de Klerk philosophy?"

He was referring to continuing speculation that the National Party may soon open its doors to black members to broaden its base of political support, just as Inkatha is seeking to do by inviting non-blacks to join.