NEW YORK -- Last October, New York City officials held a special auction of 27 heavily discounted taxi medallions that could be used only with cabs powered by natural gas or by a combination of gasoline and electricity, according to the New York Times. Eighteen of the licenses were sold, at an average price of $222,743, one-third less than the cost of a regular medallion. The Taxi and Limousine Commission praised the program as a first step toward the reduction of harmful emissions. One problem: The commission never got around to approving any alternative-fuel vehicles for use as taxicabs. It is now trying to back away from the sale, asserting that there are no gasoline-electric hybrids on the market with enough interior space and legroom for passengers. After months of talks with the city, the three winning bidders have filed a lawsuit, asking a judge to order the completion of the sale or award damages for breach of contract. The city's Law Department contends that the bidders never had a valid contract. The three bidders, Russian immigrants, have hired a Washington-based law firm and a former State Assembly speaker, Mel Miller, to plead their case. Environmentalists have accused the commission of backpedaling on its promises.