POLOKWANE, South Africa - South African President Thabo Mbeki received a stinging rebuff yesterday from backers of his bitter rival, Jacob Zuma, in the lead-up to a leadership vote at the national conference of the ruling African National Congress.

Moments after Mbeki's speech, his last chance to win support, thousands of delegates signaled their disapproval by standing up and singing Zuma's trademark song, which loosely translates as "Bring Me My Machine (Gun)."

Mbeki warned the conference delegates that disunity and corruption was threatening to destroy the ANC, which is facing the ugliest leadership contest in decades.

"Certain negative and completely unacceptable tendencies have emerged within our movement, which threaten the very survival of the ANC as the trusted servant of the people it has been for 96 years," Mbeki said.

Results of a vote by 6,000 delegates are expected today. Mbeki is barred from seeking reelection when his term as national president expires in 2009, but wants to be reelected as party president in order to choose his successor.

Zuma, known as JZ in the party, has emerged as the front-runner in today's vote, and would be Mbeki's likely successor as national president should he win.

Mbeki sacked Zuma as deputy president of the country in 2005 over corruption allegations, and Zuma was acquitted of rape last year. He may still face corruption charges over alleged kickbacks related to a multibillion-dollar arms deal.

In a gibe at his rival, Mbeki said that for some, obtaining a party leadership job was a way to get rich and take kickbacks in return for contracts.