* Some 30 Russians face up to eight years' jail over clashes
* Critics say Putin is cracking down on dissent
* Pre-trial hearing for 12 defendants
Twelve Russians who could face long prison terms over clashes with police at a protest against President Vladimir Putin go before a judge on Thursday, in a case Kremlin critics liken to Soviet-era show trials of dissidents.
The pre-trial hearing in the "Bolotnaya" case, named for the Moscow square where violence broke out at a rally the day before Putin was sworn in for his third term in May 2012, opens a new page in what his foes say is a determined clampdown on dissent.
Putin has signed laws activists say restrict freedoms, civic groups are under pressure from prosecutors and prominent opposition leader Alexei Navalny could be sentenced to 10 years in prison in a trial he says is politically motivated.
Now the "Bolotnaya" defendants could face similar fates. Charged with "mass disorder", violence against police, or both, some could be imprisoned for eight years if convicted.
"This is a Stalin-style trial," said Georgy Satarov, a former aide to the late President Boris Yeltsin and now head of INDEM, a think tank. "This is revenge ... It's an attempt to use fear to stop the growth of the protest movement."
The rally followed a wave of peaceful protests that erupted in December 2011, fuelled by claims of electoral fraud and dismay over Putin's decision to return to the presidency until at least 2018 after a stint as prime minister.
The protests were the biggest of Putin's 13-year rule, but they have dwindled. The pre-trial hearing comes before a planned protest march on June 12 on a route ending at Bolotnaya Square.
Defendant Andrei Barabanov, one of a total of nearly 30 people facing trial or prosecution over the May 6, 2012 protest, was dragged away so roughly by police that an ambulance had to be called for him.
"I am a normal guy - until May 6, I'd never been arrested," he said at a recent hearing over his pre-trial jailing.
Barabanov, 22, was released the next day but commandoes came for him three weeks later and he has been in custody ever since. The boyish-looking artist, who like most of the others has no prior criminal record, contends he did nothing but defend himself.
The police say protesters turned on them with flagpoles and metal crowd barriers, and that some tore up chunks of asphalt and hurled them at them. They said more than 40 officers were hurt.
Satarov co-authored a report by public figures and human rights advocates, based on video footage and witness interviews, that accused police of using excessive force and squeezing protesters into a confined space, causing panic.
"What I saw was mass disorder on the part of the police," said Barabanov's girlfriend Yekaterina, who declined to give her last name. She called the case a "huge pile of lies".
"We were there together so I have no doubt that the charges are absurd, lawless, disgusting and vile," she said.
"He is not a political activist, he is like most of us - people who went to the demonstration because we were fed up," bestselling detective novelist Boris Akunin, who has spoken at several protests, said of Barabanov in a video statement.
"It is absolutely clear that everything has been decided ahead of time and as a result Andrei Barabanov will be jailed."
Putin, who denies he is seeking to stifle dissent, has said that people have the right to protest peacefully but that it is unacceptable to raise a hand against police.
A lawyer for 27-year-old journalist Leonid Kovyazin, who prosecutors say overturned a portable toilet to build a barricade against police, said the charges were overly severe.
"At most this is s minor hooliganism and the destruction of property. Usually, it's a fine," Ruslan Chanidze said.