A federal judge challenged Mayor Michael R. Bloomberg’s efforts to improve air quality in the city, preventing a rule that all new taxis must meet stringent fuel efficiency standards.

The rule would have made it imperative for cabs to be hybrid gas-and-electric vehicles by 2012. The city responded to the judge by signaling that it would seek to achieve similar results by other means.

Fleet owners and other industry members filed a lawsuit against the rule, which is a major component of the mayor’s effort to make city policies more environmentally responsible.

The judge, Paul A. Crotty, issued an injunction to stop the city from enforcing the rule because, he said in a written order, the plaintiffs were likely to succeed in a key legal argument, that only the federal government has the right, under existing laws, to set fuel efficiency standards.

Mr. Bloomberg said in a written statement: “We are very disappointed in the decision.”

The statement also said that the city was considering an appeal of the judge’s order. “The decision is not a ruling against hybrid cabs, rather a ruling that archaic Washington regulations are applicable and therefore New York City, and all other cities, are prevented from choosing to create cleaner air and a healthier place to live.”

Currently, cabs must be replaced after three to five years, depending in part on how frequently they are driven. The city is considering a rule that would reduce the number of years that less fuel-efficient cabs would be allowed to remain on the road.

Many in the taxi industry have resisted the change, however, claiming that the available hybrids were not designed for the rough-and-tumble of New York cabs and were more prone to breakdowns. They’ve also argued that the smaller hybrids are not as safe.

The decision said that the federal government set fuel efficiency standards under the Energy Policy and Conservation Act of 1975, which bars state and local governments from setting their own, competing standards.