Prominent Russian blogger Alexei Navalny was released from prison Wednesday, adding another voice to an opposition movement ahead of a Christmas Eve rally that organizers hope will be the largest since the fall of the Soviet Union.

But his reemergence provided no more clarity to a movement whose chances of success remain uncertain.

Navalny, 35, was arrested for blocking traffic during an unauthorized protest the day after contested Dec. 4 parliamentary elections that pushed thousands of Russians into the streets. The force of their frustration has surprised many in the country, but the future remains deeply unclear, analysts said Wednesday. Saturday’s demonstration will be a measure of the opposition’s energy ahead of presidential elections scheduled for March.

Navalny wrote on his blog Wednesday that he was arrested in one country “and released into another,” and his Web site filled with more than 1,000 comments from supporters in just a few hours.

But the organizers of the demonstrations — a mixture of old-line opposition groups and young bloggers — have been able to agree on what they don’t want — corruption and Prime Minister Vladimir Putin — more than on what they do want. Some organizers conceded Wednesday that the scale of their success so far had shocked even them.

“For so many years we blamed the Russian people for doing nothing, for not taking to the streets, for not caring about politics,” said Ilya Klishin, a blogger who has been organizing social media for the protests. “Now they’ve taken to the streets. It’s a real challenge, what to do with that. We’ve called for it and here it is.”

Though many of the Internet-savvy protesters had hoped Navalny would file to run for president, their hopes were dashed after Russia’s reformist political party nominated one of its longtime leaders instead. Navalny said Wednesday that he wouldn’t have wanted to participate in elections that he does not believe will be clean.

The deadline to file to run for president was Tuesday, leaving Putin running against Communist Gennady Zyuganov; nationalist Vladimir Zhirinovsky; Sergey Mironov, a longtime Putin ally, and a handful of independents who will have to collect 2 million signatures by Jan. 18 if they are to qualify for the ballot.

Among those who must collect signatures is Mikhail Prokhorov, the billionaire owner of the New Jersey Nets who is running on a pro-business platform, and the reformist Grigory Yavlinsky.

Of those candidates, only Prokhorov has not previously run for president, contributing to a sense among young activists that their main goal in March will be to vote against Putin, not enthusiastically to back another candidate. Analysts doubt that Putin will lose but say his standing could be damaged if he fails to capture 50 percent of the vote on the first ballot and is forced into a second round.

“Real opposition could be formed during the first few years of Putin’s presidential term,” said Mark Urnov, dean of political studies at the Higher School of Economics in Moscow. “His popularity is going down steadily.”

Navalny’s stature was helped by his 15 days in prison, but he remains one leader among many. Prior to his arrest, he had been unknown to the vast majority of Russians, who get their news primarily from Putin-sympathetic television channels. Still, some have questioned whether his sometimes stridently pro-ethnic Russian politics would sit well among the more liberal crowd that has thus far been his source of support.

In comments made to a boisterous crowd of more than 100 supporters and journalists just after he left jail, Navalny said he may be interested in running for office at some point.

“We will fight for the declaration of a free election,” Navalny said. “Many different people will take part in such a free election — perhaps I will, too. I will compete for a leadership position.”

On Wednesday, the protesters got a boost when Mikhail Gorbachev, the last leader of the Soviet Union, announced that he would speak at the rally. The gathering is taking place on the eve of the 20th anniversary of Gorbachev’s resignation, and with it, the end of the political system he led. Gorbachev is far more influential outside Russia than within, where he is largely disliked, though the young protesters have rekindled an interest in him.