A Moscow court will pass judgement on Friday on three women from a tiny punk band who captured global attention by defying the Russian authorities and ridiculing President Vladimir Putin in a church.

Pussy Riot release rallies have stretched from Sydney to New York as a growing list of celebrities joined ex-Beatle Paul McCartney and pop icon Madonna in a campaign directed against Putin's crackdown on most dissent.

The band mates - two of them mothers and none older than 30 - have been held in pre-trial detention for five months and face three years of corrective labour on a charge of hooliganism motivated by religious hatred.

The three have already asked the faithful to forgive them for causing insult but vigorously defended their view that Russia had made little progress in the 12 years of Putin's domination from the worst of its totalitarian days.

"I do not believe in this court. There is no court. It is an illusion," band member Nadezhda Tolokonnikova said in reference to Russian judges' propensity to toe the Kremlin line in big cases.

But the 22-year-old stressed that she would never ask Putin for a pardon. "Let him ask you and me for forgiveness instead," she told the opposition Novaya Gazeta paper in an interview published to coincide with the verdict.

The 'Punk Prayer' trio performed in balaclavas and short neon dresses near the altar of Moscow's biggest cathedral on February 21 belting out a raucous chorus calling on the Virgin Mary to 'drive out Putin'.

The judge will convene the session at 11:00 GMT under tight security and is likely to rule quickly on their guilt before taking hours to read through the case material and eventually reaching the sentencing phase.

The verdict is being delivered in the same week that Putin marks the first 100 days of a third Kremlin term he has already used to slap new fines and restrictions on protests and political organisations with foreign sources of income.

Yet the moves - all stemming for Putin's charge that Washington was funding the historic protests that rose against his return to the Kremlin this winter - appear to be backfiring.

A poll published on the front page of the Vedomosti business daily on Friday showed Putin's approval rating slipping to a post-election low of 48 per cent - a notable slide from the 60 per cent he enjoyed around his May inauguration.

The former KGB agent's return to a Kremlin post he used to centralise power in 2000-2008 has been repeatedly punctuated by tense diplomatic exchanges with Western governments fearful about the future of free expression in Russia.

The US State Department has already angered Moscow by expressing formal concern about the 'politically motivated prosecution of the Russian opposition'.

The unusual case has also highlighted the political sway enjoyed by the Russian Orthodox Church in the formally secular country and the danger it faces of estranging the younger generation it must foster for future growth.

A poll conducted by the respected private Levada Centre shows opinion has shifted firmly in the singers' favour after the public initially backed a full seven-year sentence applicable to the crime.

Even some Church members now concede that it might be wise for the clergy to be less hostile toward the first concerted post-Soviet protest movement that rose against Putin this winter on news of his impending Kremlin return.

"The voice of extremism is now being viewed as the voice of the Church itself," the reformist Archdeacon Andrei Kurayev wrote in his blog.