Congress of South African Trade Unions (Cosatu) general secretary Zwelinzima Vavi has reopened the African National Congress (ANC) succession debate, saying that any effort to stop Deputy President Jacob Zuma becoming the party's next president would be like "trying to fight against the big wave of a tsunami".

His call for Cosatu members in the ANC to discuss the succession issue openly comes against the backdrop of attempts by the ANC to play down the issue on the grounds that the organisation does not have to choose its next leader until the ANC's conference in 2007.

Zuma is deputy president of both SA and the ANC, and his lobby within the ANC argues that making him party president in 2007 would allow him to succeed President Thabo Mbeki as the country's first citizen in 2009.

Vavi said yesterday he was speaking in his personal capacity, but his voice is likely to carry weight in the union federation as many of its 1,7-million members are also ANC members.

His comments follow the warm reception given to Zuma by Cosatu members at a conference on Saturday. Members sang Zuma's praises, and accused former prosecutions chief Bulelani Ngcuka of trying to discredit Zuma through the Scorpions investigation of Zuma's financial adviser, Schabir Shaik.

Asked to explain his apparent endorsement of Zuma, Vavi said yesterday he was merely trying to explain Zuma's popularity with Cosatu's rank and file.

"I was trying to interpret the deputy president's popularity, which I have seen at this conference," he said.

Vavi said: "We have been calling on Cosatu members who are members of the ANC to discuss the (succession) question. Cosatu cannot be involved.

"Even though some Cosatu regions have a position on this issue, it is for the ANC to decide."

Vavi's comments and Zuma's warm reception at the weekend are the best news Zuma has received since Shaik took the witness stand in his corruption and fraud trial two weeks ago.

Shaik has made a number of concessions in the witness box that have embarrassed Zuma, and it could severely harm his presidential aspirations if Shaik is found guilty.

The embattled Zuma has the support of the increasingly marginalised ANC Youth League, and Vavi's comments are likely to come as a shot in the arm.

Cosatu is a part of the ruling tripartite alliance with the ANC and the South African Communist Party, but the alliance has diminished in importance in the past 10 years.

A former unionist now in government said Vavi's views had to be understood in the context of attempts by current unionists to prepare themselves for life after the unions.

"Many unionists are worried about what is going to happen to them when they leave the unions. Age is catching up with them, and some have not bettered themselves academically. They are worried," said a former unionist, who declined to be named.

Political analyst Aubrey Matshiqi said the ANC was not likely to consider what Cosatu said when it chose its next president

"I don't think Cosatu's support for this or that candidate would sway the ANC when it makes its decision."

Matshiqi said Zuma was always received warmly at Cosatu conferences. "What Vavi said is in concert with what ordinary members of Cosatu feel about Zuma."

Judith February of the Institute for Democracy in SA said the importance of debating who should become SA's next leader extended beyond the ANC.

She said there was an urgent need for debate on the succession issue and the kind of leader that SA would need when Mbeki stepped down in 2009.

"It is open season for people to get behind their preferred candidates. It is in the nature of politics for there to be a level of posturing and people positioning themselves."

With acknowledgements to Ernest Mabuza, Sapa and the Business Day.