JOHANNESBURG, South Africa (AP) _ The leader of the Inkatha Freedom Party today rejected an olive branch from the rival ANC, dimming hopes for a deal to avert a boycott of South Africa's first all-race election in April.

A spokesman for the conservative opposition Freedom Alliance, which includes Inkatha, expressed optimism over the ANC proposals announced Wednesday night. But Inkatha is the largest member of the Alliance, and it was doubtful the coalition could accept any deal without approval from Inkatha leader Mangosuthu Buthelezi.

Freedom Alliance members were expected to meet this week to come up with a formal response to concessions announced by Nelson Mandela, president of the African National Congress, the country's largest political group.

Mandela told a news conference the ANC had dropped its demand for a single- ballot system in the April 26-28 election to end white-minority rule. He called for multiparty negotiations to be reconvened next week if possible to approve the decision.

This marks an important concession to the anti-ANC Freedom Alliance, whose threat to boycott the election have raised fears of violence during the campaign and after the vote. The Alliance has said voters should cast two ballots in April - one for a national Parliament and another for regional legislatures.

This would give small, regionally based parties such as those in the Alliance a chance of establishing power-bases in their areas of support. A single ballot would have virtually assured the huge ANC a majority of seats in both the national and provincial legislatures.

Mandela also said the ANC approved amending the new constitution to clear the way for consideration of a white homeland after the election. He didn't give details, but said the ANC supported the all-white Parliament being recalled to incorporate this clause in the interim constitution approved in December.

Right-wing whites, allied with the Zulu-based Inkatha in the Freedom Alliance, demand that whites be given a homeland. Alliance members have threatened civil war if their demands aren't met.

''We must treat the threat of civil war seriously. That is why we have gone out of our way to make these concessions,'' Mandela said.

At a separate news conference, President F.W. de Klerk said Parliament could be recalled in March to ratify the changes. He said he hoped the Freedom Alliance would ''place the interests of South Africa and of its voters first'' and accept the concessions.

But Buthelezi said Mandela's statements failed to address Inkatha's opposition to the election plan, whereby voters would choose a government with the task of drafting a permanent constitution to replace the interim one.

''What utter hypocrisy,'' he said. ''Mr. Mandela's statement amounts to no more than cheap politicking on life and death issues.''

Inkatha has opposed the idea of an interim constitution because it fears any concessions it wins on amending the document would be scrapped when the next government - expected to be led by the ANC - drafts a permanent constitution.

Inkatha says a permanent constitution, guaranteeing regional autonomy for its Zulu followers, should be ratified before the election.

Despite the concessions, Mandela made clear the ANC's opposition to ethnically based homelands remained.

''Our position is that of a united South Africa,'' he said.