In the early stages of the campaign for mayor, the candidates have expressed little enthusiasm about the expansion of bike lanes, and a few have made comments that suggest they may seek to erase some of them.

The concern is noted even in the Bloomberg administration, where some speak of invisible countdown clocks in every city office, reminding officials of the dwindling time to complete projects.

“Three-hundred and twenty-nine days,” Janette Sadik-Khan, the city’s transportation commissioner, said in a recent interview. “There’s an app where you can have it on your phone.”

In a poll by The New York Times in August, 66 percent of New Yorkers said the bike lanes were a good idea; 27 percent called them a bad idea.

Asked about the candidates’ apparent reticence on bikes, Ms. Sadik-Khan said, “A lot of people would like to see their numbers polling like bike lanes.”

And yet, cycling advocates find themselves straining to persuade any prospective successor to Mr. Bloomberg to expand upon, or even to preserve, the gains made under his watch.

John C. Liu, the city’s comptroller and a likely Democratic candidate for mayor, said in a phone interview that removing existing lanes would be “a likely scenario in some parts of the city,” particularly in Brooklyn and Queens, if he succeeded Mr. Bloomberg.

While calling himself “an avid bike rider,” Mr. Liu expressed skepticism about the polling numbers on bikes. “It depends who’s doing the poll,” he said. “I don’t recall any opponents of bike lanes conducting any polls.”

Joseph J. Lhota, the former chairman of the Metropolitan Transportation Authority and a Republican candidate for mayor, also said he “could see” removing lanes that he deemed problematic. He noted that some bus drivers along the B63 route in Park Slope, Brooklyn, had complained about the perils of sharing space with bike riders.

In recent weeks, two of the Democratic front-runners in the race for mayor, Christine C. Quinn and Bill de Blasio, have faced criticism for their public comments on bikes.

In January, Ms. Quinn, the City Council speaker, told WNYC that she placed bike lanes “in the category of things you shouldn’t discuss at dinner parties,” alongside money, politics and religion.

“I think it’s a funny joke,” she said in an interview on Thursday, adding that now “it’ll be completely dead as material.”

Mr. de Blasio, the city’s public advocate, drew the ire of bicyclists last week after an interview with The Brooklyn Paper. Where bike lanes have worked, he said, “great, let’s keep them,” but “where they haven’t worked, let’s revise them or change them.” He also suggested that the city should consult “actual evidence, not biased evidence” in appraising the effectiveness of its lanes.

Paul Steely White, the executive director of Transportation Alternatives, a group that has gained considerable influence in the Bloomberg years, attributed the candidates’ positions on bikes to political “laziness.”

“There’s this meme, this myth, that Bloomberg has crammed bike lanes down people’s throat,” Mr. White said. “I get that Bill de Blasio and others are striving to distinguish themselves from Bloomberg. My advice to them is to pick another issue.”

Howard Wolfson, a deputy mayor, also suggested on Thursday that any mayoral hopeful would be unwise to reignite a settled debate, saying, “The great bike war is over, and the opponents lost.”

There are signs that some candidates have begun tacking toward a softer stance. Cyclists remember William C. Thompson Jr., a former comptroller and a likely Democratic candidate, for pledging, during a 2009 campaign against Mr. Bloomberg, to rip out a bike lane on Grand Street if he was elected. In an interview last week, he said he had no intention of removing lanes, and added that he would even consider expanding bike projects if the bike-share program, scheduled to begin in May, proved successful.

In her remarks to WNYC, Ms. Quinn called the city’s lanes “clearly controversial,” and said that some had been constructed “without consultation with communities and community boards.”

But Ms. Quinn said last week that the Transportation Department had begun to work more collaboratively with neighborhoods on bike lanes since the City Council passed a law in 2011 requiring the department to “hold hearings with affected community boards before a bicycle lane is constructed or removed.”

Ms. Quinn also said she supported cycling in general, and rode occasionally near her weekend home in New Jersey. “My district is crazy for bike lanes,” she said.

In a statement this week, Mr. de Blasio said that he wanted to see bike lanes expanded, but that the city “still hasn’t come around to proactively engaging those who are concerned by them.”

In the city’s history, Gracie Mansion has had a checkered record on cycling. Mayor Edward I. Koch, inspired by a trip to Beijing, installed experimental cycling lanes of his own in 1980, but later removed them. In 1987, he moved to ban bicycle use on sections of Park, Madison and Fifth Avenues during many weekday business hours.

Even now, support is rarely unanimous. At a recent community board meeting on extending a lane on Columbus Avenue, a 10-year-old boy named Oscar told the crowd that he and his younger brother needed a safe way to bike to school.

The crowd cheered, the boy smiled, and a woman near the back of the room slumped in her chair.

“Oh, God,” she grumbled.