* Successor choice -- "old guard" versus new managers?
* Nazarbayev to retain power
* Nazarbayev's stability appeals to Western investors
ALMATY, March 28 (Reuters) - When he secures another five years in office on Sunday, Kazakh President Nursultan Nazarbayev will also win time to answer the question on everybody's lips -- who will succeed him? The 70-year-old former steelworker has steered his oil-producing Central Asian nation with an iron hand since Soviet times, brooking no dissent while putting in place market reforms and overseeing foreign investment. He left many of his critics and loyalists speechless when he set an early election for April 3 -- a move some political analysts say was aimed at preventing a challenge from within his inner circle, rather than from the disparate opposition.
He is expected to win the presidential election easily.
Allowed by law to run for an unlimited number of terms, Nazarbayev has said he will rule for as long as he is fit. He also enjoys the official title "Leader of the Nation", a status that will allow him to shape policy even after retirement.
He is still quick-witted and in good physical shape, but his age has given rise to speculation over possible successors. He has no sons who would make obvious candidates and no strong opposition candidate has ever emerged in Kazakhstan.
"He has learnt so deftly to manipulate the people surrounding him by creating rumours that either one person or another could succeed him," Alexei Malashenko, a programme co-chairman at Moscow's Carnegie Centre, told Reuters.
"So whatever name could be named today, the real successor would still not be visible, which creates a certain vacuum between him and the others and allows him to reign undisturbed."
Speculation in the steppe nation five times the size of France, which has built warm ties with neighbours Russia and China, and with the West, has so far focused on six or seven people.
These include experienced diplomat Kasym-Zhomart Tokayev, recently appointed to head the United Nations office in Geneva; Imangali Tasmagambetov, mayor of the capital Astana; and Timur Kulibayev, a billionaire son-in-law of Nazarbayev.
But presidential aide Yermukhamet Yertysbayev told Reuters he believed Nazarbayev would rule at least until 2020. Then "honest and transparent elections will take place ... and the president will probably be someone who is not yet known."
A successor may be plucked from the thousands of young Kazakhs who have been trained in leading Western universities on the Bolashak programme -- Kazakh for "future" -- personally overseen by Nazarbayev. Many have become prominent managers in state-run and private companies.
"Compared with us, they have an elite Western education, can speak three languages and work actively for themselves, in government, in state companies, in business," Yertysbayev said.
Nazarbayev's successor would run Central Asia's largest economy, which is also the world's No. 1 uranium producer and a major producer and exporter of oil, industrial metals and grain.
But some political analysts said Nazarbayev would retain his grip on the nation of 16.4 million people and its natural riches even after stepping down formally.
"The post of president could be scrapped, and Kazakhstan could turn into a sort of parliamentary republic, where Nazarbayev's Nur Otan ruling party would dominate all facets of life," said Kazakh political analyst Andrei Chebotaryov.
"As 'Leader of the Nation', he would control the legislature and appoint prime ministers through his party."
Nazarbayev, popularly nicknamed "Papa", has repeatedly expressed his admiration for Lee Kuan Yew, the founder of modern Singapore and its ruling People's Action Party, which has never lost an election and has ruled since independence in 1965.
Lee, aged 87, holds the post of minister mentor and exercises considerable influence over the city-state.
Nazarbayev is proud of preserving what he calls "stability and harmony" in his multinational, majority Muslim country, and presents Kazakhstan's robust economic growth as the main legacy of his rule in a volatile region bordering Afghanistan.
Criticised by the West for backtracking on democracy, he is unlikely to make any significant political changes during his next five years in office, "especially if close ties with Russia prevail", said Malashenko from Moscow's Carnegie Centre.
European and U.S. businesses have made up the bulk of the $150 billion in foreign direct investment in Kazakhstan under Nazarbayev, although China has played an increasing role in the last few years.
"I fear most of all that the Europeans and Americans have already become accustomed to both Uzbekistan and Kazakhstan and will make no serious effort for reforms there," Malashenko said. (Additional reporting by Raushan Nurshayeva in Astana; editing by Elizabeth Piper)
ALMATY, March 28 (Reuters)