The city took a tentative step this week toward fulfilling the dream of a certain kind of urban idealist, saying that it will explore the possibility of creating a bike-sharing program that could make hundreds or even thousands of bicycles available for public use.

“This is a really big deal,” said Wiley Norvell, a spokesman for Transportation Alternatives, an advocacy group for cyclists, pedestrians and transit riders. “In the realm of things you can do to boost bicycling in a city, bike-share is at the top of the list.”

The city asked companies and organizations interested in running a bike-sharing program to provide assessments of how it could work.

A similar program was started last year in Paris, using thousands of bicycles. A program with 120 bicycles was started earlier this year in Washington.

On many mornings, as commuters pack themselves into subway trains and drivers squeeze onto the streets, Janette Sadik-Khan, the commissioner of the Department of Transportation, rides her bicycle to work.

That the head of an agency long associated with car travel is an avid bicyclist symbolizes what might be a new way of thinking about how New York's asphalt should be used. In recent months, the city has pledged to add bicycle racks and hundreds of miles of bike lanes on city streets and has been exploring a program similar to one in Paris in which people can use bikes at minimal cost.

The Bloomberg administration says it wants to develop cycling as a viable transportation alternative to ease traffic congestion, reduce carbon emissions and encourage physical activity. But the new attention to cycling has also encountered resistance in some neighborhoods, especially when it threatens to remove traffic lanes for cars and trucks.

Ms. Sadik-Khan said her time on two wheels has become an important part of her work.

"It's invaluable to get on a bike and see firsthand the conditions that our projects are trying to address," said Ms. Sadik-Khan, who became the city's transportation commissioner in the spring. "We are really emphasizing connectivity in the bicycle lane network, because all cyclists, myself included, know that it's maddening to be coming along a lane and have it simply end and leave you off on your own on a big avenue."

To that end, the Bloomberg administration has said it will add 200 miles of bike lanes by 2010 - the equivalent of the number added during the last 20 years.