* Metals tycoon may lead pro-Kremlin liberal party
* First oligarch to enter Russian politics since 2003
* Right Cause boss says to support Prokhorov for leader
(Adds Prokhorov quotes in paras 10-13)
By Anastasia Lyrchikova
KALUGA, Russia, May 16 A Russian billionaire declared on Monday he sought to lead a party backing a second term for President Dmitry Medvedev, a move that could undermine an unwritten rule that tycoons stay out of politics.
Prime Minister Vladimir Putin, expected by many to run for president again in elections next year, cracked down on powerful "oligarchs" during his eight years in the Kremlin. Oil magnate Mikhail Khodorkovsky was stripped of his fortune and imprisoned. Others have left the country. Mikhail Prokhorov, one of those who has made his peace with the Kremlin, said on Monday he hoped to lead Right Cause, a party with a mainly middle-class constituency which supports a liberal free market economy. It has no seats in parliament and was formed only two years ago.
"I have sent my proposal to the leadership of the Right Cause party," Prokhorov, owner of the New Jersey Nets basketball team, told a reporter during a trip to a power station in Kaluga, 150 km (90 miles) south of Moscow.
"Now the decision is with them," said Prokhorov, who was ranked second in a list of the richest Russians by business magazine Finans with a fortune of $22.7 billion.
Prokhorov, a whiz-kid of Russian finance who is sometimes called Moscow's most eligible bachelor, earned a fortune by selling a one-quarter stake in mining film Norilsk Nickel (GMKN.MM) just before the 2008 global crisis.
He has a 17 percent stake in RUSAL (0486.HK), the world's top aluminium producer, and a 30 percent stake in Russia's top gold producer, Polyus Gold (PLZL.MM) PLZLq.L.
On the face of it, Prokhorov is challenging the tacit deal reached under Putin that oligarchs eschew the political power they enjoyed in the 1990s after amassing fortunes with the collapse of communism and sell off of state-owned enterprises.
But analysts said that although he is the first oligarch to openly back a party with a preference for Medvedev in the 2012 presidential election, the move could be intended by the Kremlin to create an impression of open political competition in Russia.
In a radio interview, Prokhorov said he had consulted neither with Putin nor with Medvedev about the decision.
He said he wanted to make Right Cause the second largest political force in Russia after Putin's ruling United Russia party, which holds 315 of 450 seats in the Duma, the lower parliament house.
Three other parties also have seats in the Duma, which is up for election in December.
"We need to fight to become the second (largest) party," he said. "Successful people want to see a party which is able to solve tasks. So I would set this goal for myself," Prokhorov told Kommersant FM radio station.
Putin is now prime minister but is still widely regarded as Russia's paramount leader since helping usher his protege Medvedev into the Kremlin in 2008 because the constitution barred him from a third successive term as head of state.
Putin created a movement this month to broaden the base of his ruling party before parliamentary elections, but Medvedev has withheld his full endorsement, increasing speculation both may want to run in 2012. [ID:nLDE74A0Y0]
Medvedev helped fuel such talk by saying on Friday Russia could face civil war or stagnation if too much power was concentrated in the hands of one man. The remark could be interpreted as a snipe at Putin, a man who did much to centralise state power following the chaos of the 1990s. [ID:nLDE74C1EE]
EARLY BACKING FOR PROKHOROV
The co-chairman of Right Cause, Leonid Gozman, told Reuters by telephone he would back the 46-year-old tycoon's candidacy.
"I am for him...Our aim is to remove United Russia's monopoly of power," he said, referring to Putin's party.
Leadership of Right Cause would make Prokhorov the first top Russian businessman to enter party politics since the 2003 arrest of former oil magnate Khodorkovsky, who is still in jail and whose company was carved up and sold by the state.
"This is a unique situation: for the first time since 2003 an oligarch, a major owner, has recognised his political ambitions," said Alexei Mukhin, a political analyst who heads the Moscow-based Centre for Political Information.
A group of oligarchs used their money and influence to help Boris Yeltsin win a second term as president in 1996 and prevent the Communists returning to power, but Putin clipped their wings early in his presidency, which ran from 2000 to 2008.
Mukhin said Prokhorov's move into politics could have been approved by the Kremlin and Putin's team. Mukhin said Right Cause could garner some of the urban professional vote while creating the perception of political competition.
"Prokhorov proposed his services and money for the Kremlin's secret desire: to befriend the intelligentsia which is in opposition," he said.
"That way he buys an indulgence from the Kremlin." (Writing by Guy Faulconbridge, Polina Devitt and Thomas Grove, editing by Timothy Heritage and Ralph Boulton)