Judge Carl J. Nichols seemed skeptical that the changes President Trump has rushed to make would irreversibly deface the pool if he later found them illegal.
A federal judge seemed hesitant on Thursday to order work on the Lincoln Memorial Reflecting Pool immediately halted and appeared eager to sort out how fundamentally the project — a top priority for President Trump — would alter the site.
During a hearing in Washington, Judge Carl J. Nichols asked whether the work underway in the pool’s basin could be reversed or undone should he ultimately find that it had been undertaken illegally.
The suit was brought by the Cultural Landscape Foundation, a nonprofit advocacy group focused on preserving historical heritage sites. The foundation sued after the Trump administration launched efforts to reline and repaint the pool blue, in what preservation and architectural groups have called the latest affront to Washington’s historical aesthetic.
This lawsuit is focused on the pool’s new color, which Mr. Trump said he chose himself. The group has asked Judge Nichols to stop work immediately, even while its suit proceeds.
Joseph Mead, a lawyer representing the organization, told Judge Nichols that the Trump administration had forged ahead without seeking approval for the project, in violation of the National Historic Preservation Act. He said the law bars the government from fundamentally changing the appearance of major landmarks without consulting preservation experts and other parties with an interest in the sites.
John Karl Heise, a Justice Department lawyer, told Judge Nichols that the changes were small, designed to deter algae growth and stop water from leaking out through the concrete bed, which was last renovated in 2012. Because the pool is not being fundamentally altered, he argued that the government was justified in using a streamlined process with minimal consultation.