MOSCOW — Russia's opposition will test Vladimir Putin's grip on power Saturday in protests across the nation's sprawling expanse that promise to be the largest demonstration of public outrage since the dying days of the Soviet Union.
Widespread reports of fraud in last Sunday's national parliamentary election have galvanized an opposition long marginalized by repressive policies and by state-run news media that virtually ignored them.
Protests, some attracting thousands, rolled on for three consecutive nights in Moscow and St. Petersburg after the election showed unexpectedly fierce anger against the government and Prime Minister Putin's ruling United Russia party.
United Russia suffered losses of more than 20 percent of seats it previously held in the State Duma, and critics and local election observers say even that result was inflated by fraud.
Smoldering resentment caught fire, largely through social media, and the country on Saturday expects to see a massive protest rally in Moscow and demonstrations in some 70 other cities.
"This will be a watershed step in the development our democracy. We expect it to become the biggest political protest in 20 years," Ilya Ponomarev of the Left Front opposition group said Friday.
There may soon be a symbol to the protests: white ribbons. A group of activists sent up a website urging people to wear them in support of Saturday's demonstrations. They're not yet visible on Moscow's streets but some opposition leaders and even TV presenters are wearing them in their lapels.
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 statements by Medvedev and Putin mollified no one in the opposition, which 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.
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 the following 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.
In a possible attempt at intimidation, a top Interior Ministry official proposed this week that all social media users be required to register their legal names and addresses.
Moscow initially authorized a protest for a maximum 300 people, but late Thursday it reached an agreement with opposition leaders to allow 100 times more if the rally was relocated from downtown Revolution Square.
The authorized protest site, Bolotnaya Square, is on a narrow, oblong island in the Moscow River out of view of passers-by in always-jammed central Moscow. It can be easily controlled by blocking the handful of bridges that connect it to the mainland.
By allowing a massive turnout, the authorities soften their image of being intolerant of political dissent. Police, who routinely crack down harshly on any opposition protest that exceeds the permitted size, will have reason to lay back. That reduces the potential for the truncheon-swinging melees that discredit the police force at home and abroad.
In turn, the opposition gains credibility from the tacit acknowledgment that anger is widespread and its expression is legitimate. If clashes with police prove to be few, critics of the opposition will have less opportunity to portray them as simply disgruntled troublemakers.
However, the compromise set off a wave of discontent within the opposition. The square that lauds revolution and features a large monument to Karl Marx has strong symbolic resonance. There are also complaints that many of those who found out about the protest on Facebook may not know of the venue change and be arrested by police if they show up at the first square.
The resentment was so strong that one of the opposition's leading figures, Evgenia Chirikova, called another prominent opposition member, Boris Nemtsov, an agent of the FSB. An opposition faction loyal to radical gadfly author Eduard Limonov, says it will try for a rally there. That would be almost certain to lead to a clash with police.
Russia's marginalized liberal opposition is plagued by factional rivalries that often weaken its effectiveness. The opposition is an uneasy melding of radicals, leftists and more Western-oriented and market-friendly figures such as Nemtsov.
But Saturday's protest is notable for the participation plans of the three parties other than United Russia that hold seats in the Duma — two of which have generally voted in lockstep with Putin's party. Their participation underlines United Russia's weakening position.
"It's not an action of one political party or another ... it is above all a civil action," Ponomarev told a news conference.
"No one should put himself in the front, no one should shout 'I'm the main one'," opposition activist Anatoly Barabanov said, a remark echoing the Occupy Wall Street strategy of gaining credibility through eschewing leaders.
But unlike Occupy Wall Street, the opposition will take to the streets with two clear demands, said Chirikova: a new parliamentary election and freedom for anyone jailed in the past week's protests.
While the Moscow protest is likely to be the most dramatic and visible, the demonstrations planned for the rest of the country can also be a key sign of whether the opposition has the numbers and energy to apply sustained pressure on the government.
In a visit to Prague on Thursday, Medvedev characterized the early protests as a "manifestation of democracy."
Saturday may show how much democracy Russia will stand for.