RUSSIANS ANGERED BY allegedly fraudulent parliamentary elections are protesting today in rallies across the country, a widespread wave of anger that tests the hold on power of Prime Minister Vladimir Putin and his ruling party.

The centerpiece is to be a massive rally in Moscow, where more than 30,000 people are expected. But demonstrations attracting anywhere from several hundred to 1,000 people took place earlier in cities in Siberia and the Far East.

Demonstrations have been called for more than 70 cities, in what is likely to prove the largest public show of discontent in post-Soviet Russia.

The protesters are both angered by reports of flagrant vote fraud in the 4 December  election and energised by the sense that the elections showed Putin and his United Russia party to be newly vulnerable. The party held an overwhelming two-thirds of the seats in the previous parliament, but its share plunged by about 20 percent in the recent vote.

That result was a significant loss of face for the party that has dominated Russian politics, and protesters say that even its reduced performance was inflated by ballot-box stuffing.

In Vladivostok, several hundred protesters rallied along a waterside avenue where some of Russia’s Pacific Fleet warships are docked. They shouted “Putin’s a louse” and some held a banner caricaturing United Russia’s emblem, reading “The rats must go.”

Police stayed on the fringes of the demonstration and made no arrests. But the Interfax news agency reported that an unsanctioned flash-mob protest in the Far Eastern city of Khabarovsk was broken up by police, who arrested about half the 60 participants.

Kremlin under increasing international pressure

President Dmitry Medvedev conceded this week that election law may have been violated and Putin suggested “dialogue with the opposition-minded” — breaking from his usual authoritarian image. The Kremlin has come under strong international pressure, with U.S. Secretary of State Hillary Clinton calling the vote unfair and urging an investigation into fraud.

The opposition predicts at least 30,000 demonstrators will assemble for the Moscow protest.

If Saturday’s protests are a success, the activists then face the challenge of long-term strategy. Even though U.S. Sen. John McCain recently tweeted to Putin that “the Arab Spring is coming to a neighborhood near you,” things in Russia are not that simple.

The popular uprisings that brought down governments in Georgia in 2003, in Ukraine the next year and in Egypt last spring all were significantly boosted by demonstrators being able to establish round-the-clock presences, notably in Cairo’s Tahrir Square and the massive tent camp on Kiev’s main avenue.

Russian police would hardly tolerate anything similar.

Attempts to block the protests have failed

In Ukraine and Georgia, police were low-profile, staying on the edges of the protests and keeping their numbers small. That’s far different from Russian police’s usual crowd-controlling method of flooding any protest zone with hundreds of helmeted police who seem to relish violence.

Opposition figures indicated Friday that the next step would be to call another protest in Moscow for next weekend, with the aim of making it even bigger. But staged events at regular intervals may be less effective than daily spontaneous protests.

The opposition is also vulnerable to attacks on the websites and social media that have nourished the protests. This week, an official of Vkontakte, a Russian version of Facebook, reported pressure from the FSB, the KGB’s main successor, to block access to opposition groups, but said his company refused.

On election day, the websites of a main independent radio station and the country’s only independent election-monitoring group fell victim to denial-of-service hacker attacks.