Vladimir Putin has methodically removed challenges to his authority since he returned to the presidency a year ago, leaving a variety of opponents facing criminal charges that keep them in detention or in court. Now, his critics say, he has taken aim at a wide swath of civic organizations in an attack that could hamper democracy-building efforts for years to come.

The Moscow chapter of an international corruption-fighting agency, sociologists conducting public opinion polls and independent election monitors are among the dozens of nongovernmental organizations that have been ensnared by a Putin-backed law that threatens to silence them. The law requires NGOs that receive money from abroad to register as foreign agents if they engage in political activity — a term so loosely defined that it has been applied to bird lovers protecting rare cranes and parents helping children with cystic fibrosis.

Its targets call the law a full-scale assault on Russia’s newly emerging civil society because the NGOs face not just fines, but also the possibility of being shut down. One Putin detractor — Vladimir Ryzhkov, a former legislator who writes a column in the Moscow Times — described a “huge special operation . . . to eliminate all independent NGOs.”

The organizations, which have been growing in number and reach, provide the foundation necessary for building democratic institutions, said Leon Aron, a scholar at the American Enterprise Institute in Washington. In 2011, Aron traveled from Vladivostok in the east to Kaliningrad in the far west to study grass-roots movements. He found a deepening understanding of citizenship and greater individual initiative.

“In order to survive in the short term, the regime is destroying the basis for modernization,” Aron said in a telephone interview. “That, to me, is the greatest tragedy of what’s happening.”

In a paper about his study, “A Quest for Democratic Citizenship,” Aron argued that the United States has enormous interest in a well-developed and vibrant civil society in Russia because of its potential to help achieve a stable democracy.

“A free, democratic, and prosperous Russia, at peace, finally, with its own people, its neighbors, and the world, is among the most important geostrategic objectives of the United States,” he wrote.

Voting monitor in cross hairs

The organization being pursued most vigorously is the Golos Association, the country’s only independent election monitor, founded in 2000 and assisted over the years by American organizations including the National Endowment for Democracy and the National Democratic Institute.

Golos’s documentation of election irregularities in December 2011 helped set off demonstrations against Putin, who accused then-Secretary of State Hillary Rodham Clinton of signaling protesters to go out on the streets.

Although other organizations have received official warnings, Golos has been fined and expects to be shut down. The association was fined $10,000, and its director, Lilia Shibanova, $3,000 — even though Golos stopped accepting money from abroad when the law went into effect in November and despite its insistence that its work is not political.

Alexander Konovalov, the justice minister, said he would ask the courts to shut down Golos if it does not register as a foreign agent. Golos’s regional branch has also been taken to court, but a decision has not been made on whether it will be fined for failure to register as a foreign agent.

Both Golos organizations have kept working, and they have just moved for the third time in the past year and a half. Yet another landlord came under pressure and broke their lease for office space.

“Our goal for the next year?” asked Roman Udot, director of the Golos regional association. “To survive.”

Sitting in a small Moscow office crammed with four desks and unpacked boxes, Udot was cheerful and determined. “We can meet in cafes if we have to,” he said.

Prosecutors accused Golos of accepting foreign money after it won a prize in December from a Norwegian human rights organization, even though it refused to accept the prize money.

“I pray we will not receive another prize,” Udot said.

Golos has assembled volunteers from all over the country who provide election information. One video on the Golos Web site shows a precinct worker taking a wad of ballots out of her shawl and stuffing them into a ballot box. Later, election officials gave that precinct an award for conducting elections so well.

Golos, Udot said, has no intention of registering as a foreign agent. “It’s absolutely crazy,” he said. “The authorities want us to come to them and say we are something we are not.”

Still, repeat violations come with a possible jail term of up to two years. And when the justice minister used the word “liquidate” in speaking of shutting Golos down, it made Udot queasy. “It’s a word from Stalinist times,” he said, “when people were disappearing. It was rather unpleasant to hear.”

An important opportunity

Hundreds of NGOs nationwide are being investigated under the law, according to Human Rights Watch, including Assistance to Cystic Fibrosis Patients in Istra, near Moscow; the Muraviovka Park for Sustainable Land Use; a crane refuge in the Far East; and, in Moscow, the Memorial human rights society, Transparency International and the Levada polling organization. More than 50 have received official warnings.

When the head of the Levada Center, which provides independent polling data, said the center might have to close rather than register as a foreign agent, U.S. Ambassador Michael McFaul tweeted support: “Since the mid 80’s @levada_ru team has conducted sociological research-the engine of science.”

Among those told to register as foreign agents is the Baikal Ecological Wave, one of Aron’s case studies. It formed in 1990 to prevent a paper mill from polluting the world’s deepest lake, which contains 20 percent of the world’s fresh water. “Not only do they try to preserve this jewel,” Aron said, “but they also help to retrain the workers and look for clean industries.”

If such organizations disappear, he said, the authorities will have lost an opportunity for a constructive relationship with citizens.

“What’s coming is senseless and destructive,” Aron said. “Civil society is the school of democracy.”