The lawsuit, filed by a group with close ties to Iris Weinshall, the city’s transportation commissioner from 2000 to 2007 and the wife of Senator Charles E. Schumer, accuses the Transportation Department of misleading residents about the benefits of the lane, cherry-picking statistics on safety improvements and collaborating with bicycle activists to quash community opposition.

Opponents have criticized the two-way bicycle lane for reducing room for cars and restricting the views of pedestrians crossing the street. The basis of the legal complaint is rooted in a state statute that allows challenges to government actions deemed to be arbitrary or unfair.

The opponents are being represented pro bono by Jim Walden, a lawyer at the firm Gibson Dunn and a contributor to the 2010 campaign of Mr. Schumer.

Officials at the Transportation Department said on Monday that they had not yet had a chance to fully review the lawsuit. But Seth Solomonow, a department spokesman, said in an e-mail that the agency stood by the project’s success.

“This project has clearly delivered the benefits the community asked for,” Mr. Solomonow wrote. “Speeding is down dramatically, crashes are down, injuries are down, and bike ridership has doubled on weekends and tripled on weekdays.”

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Brad Lander, a City Council member whose district overlaps part of the lane, conducted a survey last year that found that more than 70 percent of residents in Park Slope, Brooklyn, supported the lane, although only about half of the residents on Prospect Park West were in favor.

“Most residents feel that Prospect Park West is now a calmer, safer street,” Mr. Lander said on Monday. “People feel calmer on it as pedestrians and, of course, as cyclists.”

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The opponents, however, disputed that safety had improved, and their suit argues that the department presented “deceptive” statistics. They also accuse transportation officials of ignoring required environmental reviews and subverting a public review process by presenting a full report on the lane only after the decision was made to make it permanent.

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“You feel it’s a fait accompli,” said Carol Linn, 61, one of the principals behind the opposing group.

The opponents also produced e-mail correspondence that they sought to portray as an effort by the Transportation Department to coordinate criticism of the lane’s opponents.

In an exchange from June, Ryan Russo, the department’s assistant commissioner for traffic management, told Aaron Naparstek, a leading bicycle advocate, that the lane “is under serious attack,” and he asked whether Park Slope Neighbors, a neighborhood group in favor of the lane, was “counterattacking” the criticism.

“There are enough important people talking to other important people for me to worry and to require neutralizing,” Mr. Russo wrote in the e-mail.

In the same exchange, Mr. Naparstek forwarded a comment he had posted to Streetsblog, the bicycle advocacy Web site he had co-founded, that described the lane’s opponents as “shameless, selfish pigs” who “need to be publicly disgraced every time they pop their heads up.” The post also contained a parody of an anti-lane pamphlet distributed by opponents.

“That’s quite enjoyable,” Mr. Russo replied, adding, with an emoticon wink, that Mr. Naparstek was now “a blog post ranter rather than a blog empire runner.”

A spokesman did not directly address Mr. Russo’s e-mails, but said the Transportation Department spoke to both supporters and opponents on its projects. Mr. Naparstek, asked about the exchange, replied in an e-mail, “I’ll admit it: I’m a little bit aggravated that a wealthy and politically connected group is working to kill a project that the community requested, that makes Prospect Park West safer.”

Oscar G. Chase, a professor at New York University School of Law who had not seen the suit, said the statute it invoked was commonly used.

“When people don’t like government decisions,” he said, “this is the vehicle they use.”