* Medvedev takes aim at oil tsar Sechin, Putin ally
* Government official: proposals looks "cosmetic"
* Investors: implementation will be key
By Guy Faulconbridge MOSCOW, April 1 (Reuters) - If Russian President Dmitry Medvedev wants to convince the world he has dared to split with Prime Minister Vladimir Putin, he may have to show more mettle.
Medvedev's call for oil tsar Igor Sechin and other Putin allies to relinquish their posts as board chairmen of state companies has stoked speculation he may be challenging his mentor ahead of the March 2012 presidential election.
It sent a strong signal, but Medvedev has floated vaguer versions of the same idea since he was steered into the top job by Putin in 2008, so the real test is how far he succeeds in whittling down their influence in practice.
Many investors and analysts believe Russia's head of state and its most powerful man are enacting an elaborate charade to give the impression of competition in a tightly controlled political system.
"I'm still of the view that the gap between Putin and Medvedev is much smaller than a lot of people think. The success of both of them depends on stability," said Roland Nash, chief investment strategist at Verno Capital in Moscow.
"There is good reason to portray a sense of conflict to enable them to execute their agenda. I don't believe we are seeing some massive split in the duopoly. But the evidence may be accumulating against me."
Medvedev's demand for the removal of ministers from state company boards came 10 days after he chastised Putin, indirectly but clearly, for comparing the U.N. resolution authorising Western airstrikes in Libya to "medieval calls for crusades".
Putin responded to the Libya criticism by saying calmly there was no division between him and Medvedev on the issue. But if Medvedev challenges the powerful clans which support Putin, he could provoke a backlash.
The stakes of taking on Deputy Prime Minister Sechin, the informal leader of a group of powerful former security service officers and conservatives around Putin, are huge.
Russia is the world's largest commodity producer and Sechin oversees energy and industrial policy.
He has been board chairman at state-controlled Rosneft, Russia's biggest oil company, since 2006, and has built it into a global energy major as well as organising the now blocked $16 billion share swap between BP and Rosneft.
COSMETIC OR REAL?
Ejecting officials such as Sechin and Finance Minister Alexei Kudrin from the boardrooms of Russia's national champions by mid-year certainly appears like a bid to curb the economic clout of Putin's allies.
But even if Sechin is removed from his unpaid post at Rosneft, he may continue to wield influence.
One senior government official told Reuters Medvedev's proposal would be taken up but would have little impact.
"Since we have been told to, we will have to go," said the source, who sits on the boards of some state-controlled companies. "But this measure is cosmetic because the government will still issue key directives."
So why do it and why do it now?
Some suspect the Kremlin's political managers are trying to toughen Medvedev's image ahead of the election to dispel fears of stagnation.
"This has been done just to attract people's attention to the elections, to create a whirlpool," said a source in the Russian oil industry. "There is nothing really behind this initiative but PR."
Putin is viewed as Russia's most powerful man despite stepping down as president in 2008 after serving the maximum two consecutive terms allowed in the constitution.
They have said they will decide together which one of them will run for president in 2012.
Medvedev's announcement on shaking up boardrooms was made in a sharply critical speech which amounted to a dissection of the growth of the state's role in the economy during Putin's 2000-2008 presidency.
The Kremlin chief said endemic graft was driving capital flight and called on Gazprom and pipeline monopoly Transneft to slash costs, which he said were higher than competitors because of corruption.
"The grip of corruption is not weakening: it is holding the economy by the neck," Medvedev said. "The result is obvious: money is fleeing."
Investors said that, if successful, Medvedev's plans could result in some of the vast state-controlled companies which dominate the oil, gas and financial sectors of Russia's $1.5 trillion economy focusing on profits rather than politics.
"This is a very credible measure and if achieved it would be fantastic but that is the question that the market may be cynical about," said Jochen Wermuth, managing partner of Wermuth Asset Management which has $300 million under management.
"I do not know whether Putin and Medvedev are laughing at everyone for thinking they are separating," he said. "Their gut instincts do seem to be different." (Additional reporting by Douglas Busvine, Thomas Grove, Darya Korsunskaya and Vladimir Soldatkin; editing by Philippa Fletcher)