The law banning American adoptions brought out the biggest crowd of demonstrators in months on Sunday as Russians angrily accused their government of playing politics with orphans, depriving them of the opportunity for a decent life.

Many thousands walked through gently falling snow and harsh cold, some carrying posters bearing the names and faces of the 420 members of the Duma, or lower house of parliament, who voted for the ban last month. Only seven voted against the measure. The word “shame” was emblazoned across the photos of the legislators who voted in favor, and the protest was organized as the “March Against Scoundrels.”

The rally came after 13 extraordinary months in Russia’s emerging political consciousness. In December 2011, demonstrators unexpectedly began rallying for fair elections, charging that the vote for the Duma that month had been distorted by widespread fraud in favor of President Vladimir Putin’s United Russia party. The authorities have fought back with repressive laws and a robust anti-Americanism.

Although leaders of the opposition joined Sunday’s march, it was cast as a civic event, not a political one. The rally seemed to rouse the opposition, bringing out stay-at-homes as well as those who had begun to avoid protest as they lost hope in its effectiveness.

“I’m against this anti-orphan law,” said Yevgeny Skvortsov, a 22-year-old student. “Children shouldn’t be caught in bureaucratic games.”

Shivering in the 14-degree air, he bore the likeness of Nikolai Gonchar, a United Russia deputy who voted for the ban, on a poster attached to a pole, as if carrying a head on a pike. Skvortsov, who is about to leave for India for a year-long IT course, said that he had gone to earlier rallies and that the passage of the adoption law had relighted his passion.

“If there’s a revolution,” he said, smiling, “I’ll be on the first flight back.”

The Duma has passed ever more restrictive laws against dissidents, who first came out on the streets because they considered the parliamentary election illegitimate. Putin began to blame the nascent protest movement on manipulative U.S. policy, accusing Secretary of State Hillary Rodham Clinton of encouraging such demonstrations. In September, the U.S. Agency for International Development was expelled from Russia. The Duma went on to pass the adoption ban and is considering a law making it illegal for Russians with dual citizenship and foreigners to criticize Russia on state media.

The adoption ban was passed in retaliation for the U.S. enactment of the Magnitsky Act in early December. The law, which imposes visa and financial restrictions on corrupt Russians, infuriated Putin and his government, but many Russians approved of it because they saw it as aimed at crooked officials rather than ordinary citizens.

“I’m very grateful to the American people for the Magnitsky law,” said Georgy Didenko, who journeyed three hours by train from Tver to join the protest. “You saved the honor of the Russian people with this law. We didn’t — you did.”

Didenko, 59, who survives by selling pens and train schedules on commuter trains, had a poster bearing the image of Valentin Romanov, a Communist deputy. Although marchers were demanding that the Duma dissolve itself in disgrace, Didenko said the goal was a demonstration of solidarity by people who care about democracy and good government.

The number of marchers was in high dispute. Police estimated 9,500, but from a standpoint at the crest of a hill, with marchers packing both sides of a wide boulevard, the crowd appeared much larger.

The 1.7-mile route led from Pushkin Square, honoring the revered poet whom every Russian can quote, to Sakharov Prospect, named after the most famous dissident of the Soviet period. There was a heavy police presence. Every few yards stood an 18-year-old police conscript wrapped in an ill-fitting black sheepskin coat and traditional felt boots, watching. Intersections were overseen by burly men of experience, backed up by blockades of snowplows, garbage trucks and water tankers.

As the protesters turned onto Sakharov Prospect, they marched past the boulderlike figure of Gennady Gudkov, who stood motionless, counting. “There’s a minimum of 60,000 to 70,000,” he said, factoring speed, length and density.

Gudkov, a former KGB officer, was a member of the Duma who went into the opposition as parliament began passing a slew of restrictive laws, including forcing activists who get grants from abroad to register as foreign agents. In June, he helped organize a filibuster in an attempt to stop a law imposing extraordinarily high fines on protesters who violated the numerous rules regulating rallies. By September, the Duma had found a way to expel him.

After a reporter began talking to him, marchers noticed, and soon a crowd surrounded him. “Thank you,” one rallygoer after another said, shaking his hand.

Marchers interviewed Sunday said the adoption of children should have nothing to do with attitudes toward America. (A Pew Global Attitudes poll found that 52 percent of Russians surveyed last year viewed the United States favorably, the same as in Germany.)

“Children have the right to have a family,” said Natalya Demidova, who had spontaneously joined the march with two friends as they left a church nearby. “This law is political propaganda and has nothing to do with reality.”

They were unimpressed by government promises that conditions would be improved for the country’s more than 600,000 orphans and that Russians would be encouraged to adopt them.

“It’s wrong to deprive children of a better life,” said Nuria Dianova, a 34-year-old doctor who was attending her first protest. She was accompanied by her husband and two children, ages 4 and 8. “They’ll allocate millions, and 25 percent will get there. The rest will disappear.”

Dianova and her husband said they watched with disbelief as the law was passed. “I have many different friends,” said her husband, Marat, “and I don’t know anyone in favor of this ban.”

Will Englund contributed to this report.