“Any additional complications will subtract from the value the M.T.A. receives, and leaving the High Line in place will have a substantial effect on that value,” Mr. Durst said.

But Friends of the High Line, an advocacy group, contends that retaining the rail structure will cost only about $800,000, with the benefits outweighing any problems.

“You don’t often have the opportunity to take a piece of the city’s industrial infrastructure and reuse it in an interesting way, to connect west Chelsea, Hudson Yards and the waterfront,” said Robert Hammond, a leader of the group. “It’ll be a great park that’ll serve the city as well as Central Park.”

At a community board meeting last week, an official with the transportation authority said for the first time that the authority supported retaining the High Line, although it also wanted to maximize revenues for rail operations. Privately, one official indicated that the authority did not want the High Line venture to cost it more than $25 million.

Elliot G. Sander, the executive director of the authority, said he was trying to work out the housing issue and had set aside land controlled by the authority outside the railyards for subsidized apartments. Officials say bidders will be asked to submit offers based on keeping or demolishing the High Line.