Russia's biggest opposition party on Friday accused the authorities of dirty tricks in campaigning for local elections to cover up a fall in the Kremlin's popularity triggered by the economic slowdown.

The Communist Party accused officials of locking its supporters out of halls where they were to hold rallies, tearing down election posters and confiscating campaign leaflets.

About 20 million Russians are eligible to vote in the round of local elections on Sunday, the first big test for the Kremlin at the ballot box since the start of a slump that has cost more than two million people their jobs.

Pollsters predict the elections will show a dip in support for Prime Minister Vladimir Putin's dominant United Russia party but no dramatic drop because most people have yet to feel the full effects of the slowdown.

"There have never been such dirty and unforgivable elections," Communist leader Gennady Zyuganov told Ekho Moskvy radio station on Friday.

"These elections are taking place against the background of (economic) crisis. We see how the situation is getting worse."

Two smaller parties, both normally loyal to the Kremlin, also alleged United Russia was using dirty tricks.

A senior United Russia lawmaker denied that and accused opponents of political posturing.

"It seems to me that this campaign has been fairly calm and there was not the tension that usually accompanies major election campaigns," said Valery Ryazansky, deputy head of the party's faction in parliament.

"The fact that, in the tough situation the country is in, people are choosing to back the leading party is not surprising."

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Russians will vote for regional parliaments in nine of the country's 83 regions and for mayors in several cities including Novosibirsk and Chelyabinsk.

None of Russia's major pollsters have conducted polls on voting intentions for Sunday's elections.

The hardest-fought race is likely to be in Bryansk region in western Russia, heart of Russia's "red belt" where the Communists have traditionally been strong and are trying to wrest control of the regional legislature from United Russia.

Russia is experiencing its worst economic slowdown in over a decade, driven by a credit squeeze and a sharp drop in the price of oil, its main export.

After years of buoyant economic growth that helped underpin the Kremlin's firm grip on power, the government predicts the economy will shrink by 2.2 percent in 2009. Many companies are idling their factories and laying off workers.

Protesters have taken to the streets in some places, but opinion polls show the high popularity ratings of Kremlin leaders -- and United Russia -- are largely unchanged.

The party will win most of Sunday's votes by a large margin but its support is likely to fall about five percent on previous elections, said Alexei Grazhdankin, deputy head of independent pollster the Levada Centre.

He said there could also be a drop in numbers of people turning out to vote -- a reliable indicator of disaffection with the government.

The slowdown though will only have a modest impact on Sunday's voting.

"The main part of the population is not yet feeling the crisis," Grazhdankin told Reuters. "People who live on the periphery, in small towns and in villages, the effects of the crisis have not reached them."