* World's top uranium miner, major oil exporter
* Election could take place in May - aide
* Uncertainty over successor the main political risk
(Edits, adds Nazarbayev's aide, analyst comment, background)
By Raushan Nurshayeva
ASTANA, Jan 31 (Reuters) - Kazakhstan's veteran leader called an early presidential election on Monday and rejected a plan to rule for a third decade, pre-empting any unwelcome parallels with authoritarian leaders in the Arab world.
Kazakhstan, a major uranium and oil exporter, had earlier suggested it might hold a referendum to allow President Nursultan Nazarbayev, 70, to rule the country unopposed until 2020. The United States has strongly criticised that proposal.
Speaking in an address broadcast on state television, Nazarbayev -- in power since 1989 and known as "Papa" in his vast steppe nation -- rejected the idea.
"I cannot create a precedent which would set the wrong guidelines for further generations of politicians," he said. "I propose holding an early presidential election, despite the fact that this will reduce my current term in office by almost two."
He made his remarks at a time when a wave of popular anger is sweeping countries in North Africa and the Middle East. The latest crisis in Egypt follows a revolt that toppled the leader of Tunisia earlier this month.
Like Egypt, Kazakhstan is a major regional economy led by a long-serving strongman leader. Yet, it has no organised opposition movement nor the political incentive to foment Egypt-style street protests.
Nazarbayev has ruled Central Asia's biggest economy since before the Soviet collapse in 1991. Kazakhstan has never held an election judged free and fair by international observes.
Many foreign investors, who have poured more than $150 billion into Kazakhstan during Nazarbayev's rule, rate the absence of a clear succession plan as the single biggest threat to political stability.
Analysts said Nazarbayev would not wish to risk alienation by abandoning the next election as he seeks to diversify the resource-dependent economy and attract a further $100 billion in foreign investment over the next decade.
"To belong to the club of developed countries, Kazakhstan needs to keep up the rules of the club and one of them is respecting basic principles of democracy," said Lilit Gevorgyan, an analyst at IHS Global Insight.
"To gain that membership, Kazakhstan should distance itself from prevalent Central Asian regressive authoritarian regimes and adopt more democratic practices, even if they are only on paper."
In his address, Nazarbayev -- once a member of the Soviet Communist Party's Politburo -- did not say when the next vote, which he is almost certain to win, would be held.
His aide, Yermukhamet Yertysbayev, said it could take place as early as May 2011. Parliament will meet on Feb. 2 and is expected to set a date.
SUCCESSION PLAN?
Many in Kazakhstan credit Nazarbayev with annual economic growth that has averaged around 8 percent over the last decade. Per capita gross domestic product, at more than $9,000, is more than 12 times what it was in 1994.
People of Kazakhstan, including the business and political elite, are more concerned with the succession. Nazarbayev may spend part of his next term in office -- which will revert to five years -- grooming a pliant successor, analysts said. "Five more years will be quite enough for him to resolve the main issue -- that of his successor -- because he is now racing against time," said Kazakh political analyst Dosym Satpayev.
Parliament had earlier voted unanimously in favour of the plebiscite after a self-styled people's initiative presented signatures late last year in support from more than half of Kazakhstan's registered voters.
By rejecting the initiative, Nazarbayev showed his resolve to secure firm Western backing and extend diplomatic gains achieved last year when Kazakhstan became the first former Soviet country to chair the Organisation for Security and Cooperation in Europe.
Nazarbayev, as first president, can stand for election an unlimited number of times. In his state-of-the-nation address on Friday, he said he plans to rule for as long as his health and his people will allow. [ID:nLDE70R0D8] (Additional reporting by Dmitry Solovyov and Maria Gordeyeva; Writing by Robin Paxton; Editing by Maria Golovnina)