POLOKWANE, South Africa - President Thabo Mbeki said Sunday that corruption, abuse of power and bitter internal divisions were threatening to destroy the African National Congress, as he battled against his deputy for leadership of the ruling party.

Jacob Zuma, currently ANC deputy president, was expected to defeat Mbeki's bid for a third term as ANC president. He would then be in the pole position to become national president at the 2009 elections, which are almost certain to be won by the ANC given its overwhelming support among South Africa's black majority.

Zuma headed into the conference with the most backing from provincial ANC groups as well as from the powerful youth and women's leagues, despite being under a continuing cloud of corruption allegations.

Voting was due to begin later Sunday, after the start of the meeting was delayed as Zuma supporters drowned out ANC chairman Mosiuoa Lekota -- a key Mbeki supporter -- with an anti-apartheid song, "Bring me my machine-gun,'' which has become Zuma's anthem. Lekota recently said that those who sang the song were "brainless or fools.''

Mbeki and Zuma sat in front of the crowd of 4,000 delegates, their body language revealing the antagonism that exists between the former partners, who are both 65 and spent years in exile during apartheid. The conference opened on South Africa's National Reconciliation Day -- but this was not reflected in the highly charged atmosphere.

Mbeki is barred by the constitution from seeking a third term as president of Africa's political and economic powerhouse. But remaining at the helm of the ANC would give him a say in who succeeds him and in the policies his successor adopts.

Mbeki sacked Zuma as the country's deputy president in 2005 after Zuma's financial adviser was convicted of trying to elicit a $70,000 bribe for Zuma to deflect investigations into an arms deal. Charges were withdrawn against Zuma but the National Prosecuting Authority has indicated it may revive them.

Zuma was last year acquitted of raping a family friend, but he outraged AIDS activists by testifying that he had unprotected, consensual sex with the HIV-positive woman and then took a shower in the belief that it would protect him from the AIDS virus.

Zuma survived both those scandals, successfully portraying himself as a victim of a plot to stop him becoming president.

In a 2�-hour speech to the conference, Mbeki described "matters'' affecting Zuma as being "one of the most difficult and painful challenges we have faced over the last five years.'' He said the ANC executive was ill-equipped to cope with such a situation as it had no experience. "All of us hope that we will and can put these matters behind us sooner rather than later,'' he said.

Mbeki outlined the economic and social gains made in the past few years -- seeking to silence critics who say he has done too little to spread the fruits of multiracial democracy to the poor.

He then turned to the political tensions in the movement.

"During the years since our liberation in 1994, 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,'' he said.

Mbeki said some ANC members resorted to fraud, intimidation and violence to increase their personal power and wealth. This was not just confined to local government level, he said, but also lay behind much of the ongoing jockeying for position in the national leadership contest.

He dismissed as "entirely false'' claims by Zuma's allies in the trade union movement and ANC Youth League that his government had centralized too much power, was intolerant of competing viewpoints and suppressed open debate, thus weakening the role of the ANC.

"All these are not true,'' he said to loud boos and hisses from delegates on the floor.