Some 580 official delegates and many more invited guests will over the next three days affirm SWAPO's future leadership, which has already been largely nominated in advance.

But the event is overshadowed by the departure of Hidipo Hamutenya, who broke with the ruling party after 46 years, citing frustrations with what he called the personality cult politics around Nujoma's 47-year-long rule over SWAPO.

His resignation, two weeks before the congress and two years before elections in 2009, is expected to pose SWAPO's sternest political challenge yet.

In a possible sign of the threat he represents, Hamutenya's defection has set off a purge of his suspected supporters from SWAPO, according to reports in the local press.

Hamutenya's Rally for Democracy and Progress could eat away at SWAPO's traditional vote base, analyst Graham Hopwood of the Namibia Institute for Democracy (NiD) said.

Hamutenya is backed by the Oukwanyama, the largest tribal grouping among the Oshiwambo people, who live in the most densely populated Ohangwena region, where many of the country's leaders hail from, he said.

While the RDP was still unknown and untested, the party could very well end SWAPO's two-thirds majority rule since 1995, he said.

"It is the biggest thing that has happened, one way or another, in Namibian politics in 17 years," said Hopwood.

But at the SWAPO get-together, there was little sign that Nujoma's or his party's popularity was fading.

"I am not available for re-election as president of SWAPO Party," he said in an opening speech to the usual adulatory applause.

"I am passing the torch and mantle of leadership ... to comrade Hifikepunye Pohamba, vice-president of the SWAPO Party."