The Union of Right Forces began criticizing Putin this fall after learning that the Kremlin would not stand by its promise, the party official said.

“At first, Kremlin spin doctors said the party would be allowed into the Duma if it refrained from criticism, but then they changed their minds and decided not to keep their promise,” said the official, who spoke on the condition of anonymity for fear of reprisal from both his party and the Kremlin.

“The party is angry, and now the only chance it has to get into the Parliament is to gather the protest vote,” the official said.

Communist and Yabloko officials said their parties had also been promised Duma seats if they vowed not to criticize Putin. All the officials would speak only on condition of anonymity.

A Kremlin spokesman said backroom deals had not taken place with any party.

“It is not up to the Kremlin to decide who gets into the Duma, but the results of the elections,” said the spokesman, Dimitry Peskov.

The Union of Right Forces, or SPS, has long been viewed as pro-Putin because of its tacit support of Kremlin policies. All that has changed in recent weeks. The party has produced a critical television commercial and, in a sharp reversal, joined The Other Russia opposition coalition for a dissenters’ march.

Speaking about SPS’s previous support of Putin during a televised debate earlier this month, the party leader, Nikita Belykh, said simply, “We were wrong.”

Analysts said the Kremlin might have ditched SPS because it threatened to take votes from Putin’s party, United Russia, which is facing an uphill battle in its goal to win by a landslide Sunday.

The senior SPS official said the party kicked off its Duma campaign in September with no plans to court voters actively. “They thought it was useless and started behaving like puppets in the hands of the Kremlin,” the official said.

A regional party official complained to a reporter on the sidelines of SPS’s pre-election convention in September that the party had bowed to Kremlin pressure by not including an independent Duma deputy, Vladimir Ryzhkov, on its list of candidates.

In the following weeks, the lines between SPS and United Russia gradually blurred in voters’ minds, and SPS realized that the Kremlin would not help it clear the 7 percent threshold to get into the Duma, the senior SPS official said.

“In the middle of the campaign, Kremlin spin doctors changed their minds, and we understood that we had been sidelined,” he said.

The first public indication of strained relations between SPS and the Kremlin surfaced shortly before the SPS convention, when Putin suggested during an annual meeting with foreign analysts and journalists that Anatoly Chubais, a party co-founder, might use his position as the head of United Energy System to bankroll SPS. After the jab, Chubais was noticeably absent from the convention.

Putin rebuked liberal parties like SPS at an event organized by the For Putin movement last week. “They want to come back, to return to power, to spheres of influence, and gradually restore oligarchic rule based on corruption and lies,” he said.

State television appears to mention only SPS in critical reports these days, unlike the Communists and Yabloko, whose activities tend to be portrayed in a neutral way. Last Sunday, Rossia’s “Vesti Nedeli” program broadcast an interview with Mikhail Barshchevsky, Putin’s representative in the Constitutional Court, who criticized SPS and said its acronym meant Sovsem Plokhaya Situatsia, or a Really Bad Situation.

Several women from the Krasnodar region told the same program that SPS had failed to pay them for distributing campaign leaflets. “How can a party that doesn’t pay its workers be allowed into the Duma?” one woman said.

The police across the country have confiscated millions of SPS newspapers in recent weeks, citing various purported legal violations.

In response, SPS took part in The Other Russia-led dissenters’ marches over the weekend in Moscow and St. Petersburg, after earlier refusing to associate itself with the outspoken, anti-Putin coalition led by the former chess champion Garry Kasparov. Kasparov and Boris Nemtsov, an SPS co-founder, were among those detained by the police during the demonstrations.

The police detained six SPS activists Tuesday for staging an unsanctioned protest in which they tried to deliver a giant plastic razor to the chief of the Central Elections Commission, Vladimir Churov, at the commission’s Moscow headquarters, said Sergei Gorodilin, a party official.

No party running for Duma seats has been as critical as SPS in the campaign this fall.

“We are against Putin’s plan and where he is taking our country,” said Nemtsov, the party co-founder. “This is why we are at the opposition.”