MOSCOW (AFP) - Russia's Communist Party mounted a campaign to oust the government in a direct challenge to President Vladimir Putin following weeks of nationwide protests sparked by drastic cuts in social welfare benefits.

The State Duma lower house of parliament's left wing said it would collect the 90 signatures required in the 450-seat chamber to hold a confidence vote on the year-old government of Prime Minister Mikhail Fradkov.

The challenge is unlikely to succeed because the chamber is dominated by the pro-Putin United Russia party that voted for the drastic cut in Soviet-era social benefits which sparked the largest protests of Putin's five-year rule.

'I see no reason for the government to resign,' said Duma speaker and United Russia chief Boris Gryzlov.

'They are just playing politics,' agreed his deputy Oleg Morozov.

The social security changes require pensioners and other disadvantaged groups to pay for public transport and basic medicines -- benefits they have until now enjoyed free of charge. They would be compensated by cash payments that irate protesters say are far too small.

Demonstrations have seen shouting pensioners bundled against the cold while blocking traffic in towns and cities across the huge country. This prompted Putin to appear on national television Monday to berate his government and the Duma for poorly thinking through the reforms.

Speculation has mounted that the spontaneous protests -- the first since the tumultuous 1990s overseen by Putin's predecessor Boris Yeltsin -- may force a humiliated president to fire either his government or top ministers over the affair.

And the Communists fanned the speculation by launching their signature drive.

'We want this government replaced. It has placed a plastic bag over the heads of all veterans,' Communist Party boss Gennady Zyuganov told Moscow Echo radio.

'Putin has just been elected. People placed their trust in him but we are seeing this trust melt before our very eyes,' he said.

The Communists will need support from the few remaining liberals in parliament -- who also opposed the hasty way in which the reforms were drafted -- and more centrist forces to succeed.

Analysts speculate that the vote will in fact take place early next month but that it would fail because the pro-Putin United Russia party that runs the chamber's floor would never vote against measures that they themselves introduced.

But the very idea of a no-confidence vote has sparked great excitement in a Russian media bored by the predictable tone of Russian politics under Putin in which the Kremlin dominates policy and where debate is rarely heard.

The Izvestia daily ran its front page with a banner headline quoting Putin as telling his government: 'These questions were not deeply thought out from all points of view.'

The article further quoted a seemingly frightened Fradkov as telling his cabinet before their meeting with Putin: 'So what are we going to tell the president?'

Izvestia wrote that 'a grave silence fell' on the meeting after Fradkov's question.

Meanwhile Christopher Weafer of the Aton Capital investment bank predicted a reshuffle because Putin needed a voters' 'support base that he, and those in the 'inner circle of the Kremlin,' will probably need to rely on in 2008 to ensure continuity of their vision of modern Russia.'

Putin's successor will be chosen that year and even some in the pro-Putin United Russia group said that the dismissal of a few ministers may not be a bad idea now that discontent was spreading across 11 time zones.

'The voluntary retirement of some minister who pushed through these reforms could ease the social situation in our country,' senior United Russia member Lyubov Slitska told the Kommersant business daily.

But other analysts said Putin has already shown that his team is staying put.

'Putin supported his government's stance on the burning political question of the replacement of in-kind welfare benefits with cash compensation,' the United Financial Group said in a research note.

The Vedomosti business daily agreed that 'Putin shielded his government' from future attacks despite the public criticism.