By Maria Tsvetkova and Gabriela Baczynska
MOSCOW (Reuters) - Russian protest leader Alexei Navalny won a rare victory on Wednesday by being accepted as a candidate in a Moscow mayoral election which he sees as a stepping stone to challenging Vladimir Putin for the presidency.
But his ability to contest September's election and the next presidential vote in 2018 depend on a judge's verdict on Thursday in the most prominent trial of an opposition figure in Russia since Soviet times.
Navalny, who emerged from anti-Putin protests last year as the opposition's most dynamic leader, could be sentenced to up to six years in jail on what he says are trumped-up charges of stealing 16 million roubles ($493,000) from a timber firm.
That would bar him from running for mayor against Sergei Sobyanin, a Putin favorite, and from contesting the presidential election in 2018, in which Putin, Russia's dominant leader for 13 years, could try to extend his rule until 2024.
Navalny, 37, did not appear at the Moscow offices where he was registered as a mayoral candidate despite his concerns that he would be barred from the ballot.
He has kept a low profile in the last few days before the verdict in his trial in Kirov, an industrial city 900 km (550 miles) northeast of Moscow, saying he would prefer to spend time with his young family.
But in a blog posting on Wednesday titled "Before the Verdict", Navalny urged supporters to redouble efforts to challenge the authorities through street protests, electoral politics and efforts to expose corruption.
"We know what to do and how to do it ... the main thing is to take courage, cast off idleness and do it," he wrote.
The post of Moscow mayor is a powerful one that could serve as a springboard to Navalny's political career. The independent Levada polling group has put him on only about eight percent support, but pundits say his chances of victory would rise sharply if he made it into a two-candidate runoff.
Opposition activists suspect Navalny's candidacy may have been permitted in order to give the authorities credibility. He expects to be found guilty on Thursday and says Putin will dictate the verdict, a charge the Kremlin denies.
The only question now, Navalny says, is whether he is sent to jail or receives a suspended sentence.
THORN IN THE KREMLIN'S SIDE
Navalny's trial has attracted more international attention than any other in Russia since oil tycoon Mikhail Khodorkovsky was jailed in 2005 on tax evasion and fraud charges after falling out with Putin.
Khodorkovsky's $40 billion company Yukos was then carved up and sold off, mainly into state hands, and he was convicted of theft and money-laundering in a second trial in 2010.
Tall and clean-cut, Navalny has captured the mood of urban youth disillusioned by Putin's long rule.
But he has also been dogged by accusations that he has nationalist tendencies and his appeal is limited outside the big cities.
"On the one hand it doesn't seem elegant to lock your political opponent behind bars, but I am sure he is no angel anyway," said Yekaterina, a businesswoman in Kirov who declined to give her full name.
Sergei, a Kirov pensioner, said: "I don't think he stole a thing but the problem is that he wants to run for mayor now, then maybe for governor or even president, so this trial is simply meant to close this chapter once and for all."
Navalny is accused over his role as adviser in 2009 to a timber company that went bankrupt in Kirov, where he was an aide to the liberal regional governor. He denies the charges.
He has long been a thorn in the Kremlin's side, in particular by helping organize rallies which in late 2011 and early 2012 became the biggest protests since Putin rose to power in 2000. However, they have since faded.
Navalny has suggested Putin ordered the trial to silence his criticism of what he calls a political class of "swindlers and thieves" and the absence of the rule of law in Russia. The Kremlin says it does not interfere in criminal cases.
(Reporting by Maria Tsvetkova and Gabriela Baczynska; Writing by Timothy Heritage; Editing by Jon Boyle)