“If this is a fiasco — and to me, a fiasco is mostly that the bikes just don’t get used — then, yeah, it’s going to tarnish the legacy,” said Charles Komanoff, a transportation economist and longtime cycling advocate in the city. “More important, it’s going to make it easier for the next mayor to backtrack.”

But if the program is an instant success, he added, “it’ll mean that almost anybody imaginable who is mayor is going to have to stick with whatever this mayor has already done.”

For all the administration’s legwork — which included hundreds of meetings with community groups, elected officials, property owners and other stakeholders, and an online feature that received more than 10,000 suggestions for bike station locations — precise demand for bike share is near impossible to gauge.

Though bike commuting has grown on Mr. Bloomberg’s watch, the most recent city figures showed that commuter cycling remained flat in 2012 during the typical riding season of April through October. In the same period, cycling had increased by 26 percent in 2009, 13 percent in 2010 and 8 percent in 2011, according to counts conducted at commuter points like the Brooklyn Bridge, the Manhattan Bridge and the Queensboro Bridge.

Some officials remain skeptical about the depth of citywide interest in cycling.

“The projections for bike share, I can’t say I buy,” said Councilman James Vacca, the chairman of the Council’s Transportation Committee. “But we have to accept them as a given at this point because we have nothing else to go by.”

Ms. Sadik-Khan dismissed the most recent in-season cycling figure as statistical noise amid years of consistent growth numbers. She also pointed to an increase in off-season cycling in recent months: From December through February, the Transportation Department said, commuter cycling increased by 23 percent over the previous year. And the bike share program has already sold more than 14,000 annual memberships, Ms. Sadik-Khan said.

Whatever the appetite for bike share, Ms. Sadik-Khan has long argued that cycling infrastructure must be built in advance of demand as a way to encourage riding. In this way, the bike share program could be seen as an inevitable outgrowth, a plan that required years of investments before becoming feasible.