By Nastassia Astrasheuskaya
MOSCOW (Reuters) - Russian election authorities on Friday barred liberal opposition leader Grigory Yavlinsky from standing against Vladimir Putin in a presidential election in March, boosting Putin's chances of winning in the first round.
A longtime Kremlin critic, Yavlinsky trails far behind in opinion polls that show Putin winning the presidency, but the refusal to let him run is a slap in the face for leaders of protests calling for fair elections and reforms.
In a decision dismissed as politically motivated by the opposition, election officials told Russian news agencies that over a quarter of the 2 million supporters' signatures required to back his candidacy were forged -- some five times higher than the permitted margin of error.
They said xerox copies were among the suspicious lists.
Reducing the number of candidates could improve Putin's chances of winning the election outright, avoiding a run-off vote if he does not receive at least half of votes cast.
The 59-year-old prime minister who ruled Russia since 2000 remains the country's most popular politician but faces unprecedented protests from urban, middle-class Russians angered at the prospect of another 12 years of Putin at the helm.
Members of Yavlinsky's Yabloko, which failed to win any seats in disputed December parliamentary elections, said the Kremlin ordered him sidelined from the March 4 vote.
"This decision by the Central Election Commission is politically biased," Yabloko party secretary Igor Yakovlev said.
"It was made by the state's top authorities to sideline a candidate who presented a real alternative to Putin."
He said the decision would also prevent Yabloko representatives from being allowed to monitor the election.
Yabloko leader Sergei Mitrokhin told the Ekho Moskvy radio that the refusal was a "flagrant violation of the law," and said the party would decide on Friday whether to appeal to Russia's Supreme Court.
Some analysts said Yavlinsky, a 59-year-old economist who has twice run for president, was barred to encourage voters to instead back billionaire Mikhail Prokhorov, a liberal contender who they say has the Kremlin's tacit support.
"Part of the 4 percent of votes that Yavlinsky got in the parliamentary elections will disappear: Some of his disappointed supporters won't vote at all and some will give their votes to Prokhorov," independent political analyst Stanislav Belkovsky said.
"The Kremlin appointed Prokhorov a liberal candidate ... to attract some percentage of votes, which would legitimize Putin's victory."
The head of the Central Election Commission, Vladimir Churov, defied protesters' calls for his resignation, defending the results of the December polls before parliament on Friday while Putin's campaign chief dismissed Yavlinski as a serious rival.
"Yavlinsky is not dangerous for anyone. He is a good man, intelligent, charming; but he is not dangerous. He does not have that many supporters," film director Stanislav Govorukhin, head of Putin's campaign headquarters, told Izvestia daily.
Putin and President Dmitry Medvedev have promised electoral reforms to ease barriers preventing small parties like Yabloko from winning seats in the future but ignored protesters' demands for an election rerun and left Churov in charge.
Seeking to keep up the pressure, protest leaders hope to lead tens of thousands of people on a march in the heart of Moscow on February 4.
Moscow city officials gave permission for 50,000 people to attend the rally following days of tense negotiations this week, but demonstrations planned in other Russian cities have yet to be given the go-ahead by authorities.
(Editing by Alissa de Carbonnel and Myra MacDonald)