State and city officials yesterday railed against the city’s plans to build a 1.5-mile spur off the no. 7 subway line, arguing that extending the line without plans for a station at 41st Street and Tenth Avenue would deliver a crushing fiscal blow to the city.

Earlier this month, the city celebrated a groundbreaking for the no. 7 line extension, which would serve the Hudson Yards and open up the far West Side for commercial and residential development. The city is footing the $2.1 billion price tag for the extension of the line to a station at 34th Street and Eleventh Avenue, and Mayor Bloomberg has said the Metropolitan Transportation Authority would pay for any cost overruns, as well as for half the cost of a second station at 41st Street.

Not building a 41st Street stop would be a “failure to provide for the area’s growing residential population,” Senator Schumer, Rep. Anthony Weiner, Rep. Jerrold Nadler, and other city and state officials wrote in a letter to the deputy mayor of economic development, Daniel Doctoroff. Failure to construct the station could add up to $500 million to the project down the line, they warned.

With most of its limited funds going toward the Second Avenue Subway and its East Side Access plan, the MTA says it cannot afford to pay for the station.

“It’s time for Senator Schumer and his colleagues in Albany and Washington to step up to the plate with adequate capital funding for the MTA so that they have the resources to provide the rest,” a spokesman for Mr. Bloomberg, John Gallagher, said.