Lawyers for the memorial operators said in their papers that the steel beam, found by rescue workers two days after the terror attacks, was an inspiration. They said workers "took solace in its symbolism as they searched for survivors and found mostly victims."

The lawyers noted that the museum is an independent non-profit corporation and decisions by its curators about what to display are not state actions subject to constitutional protection.

"But even if the independent decisions of a non-governmental body could constitute state action, there is no legal authority for the proposition that a museum is prohibited from displaying an item with historical, cultural or artistic significance merely because that item also has religious significance," the lawyers said.

They accused the atheists group of seeking "to revise history to eliminate religion from its retelling, ignoring the fact that the people most closely tied to the September 11 tragedy responded in varied ways, including, in some cases, turning to their respective faiths."