A panel tasked with reviewing changes to Washington landmarks voted unanimously on Thursday to give preliminary approval to President Trump’s plan to build a 33,000-square-foot visitor screening center on the White House grounds. The panel, the National Capital Planning Commission, still has to take a final vote but is expected to advance the project, as it has Mr. Trump’s other proposals to remake the White House and Washington.

Led by allies of Mr. Trump, the planning commission has approved his White House ballroom project as well as plans for a 250-foot-tall triumphal arch that would violate a height limit on structures in the city. Unlike the 90,000-square-foot ballroom, however, the new center was initially proposed as a low-profile facility where the Secret Service could screen visitors. Its entrance would be at Sherman Park, southeast of the White House, and the facility would be partially underground.

Mark Paoletta, whom Mr. Trump recently installed as the chairman of the panel, stressed how the new center would replace the temporary trailers the Secret Service now uses to screen visitors, which he said detract from the “beauty and character” of the White House. “It is evident that a more permanent, thoughtfully designed facility is much needed to welcome visitors,” Mr. Paoletta said. But even with the project moving ahead, many details seemed murky.

The commissioners also heard concerns from the public regarding the administration’s proposal to install permanent fencing, eight to 10 feet tall, around Lafayette Park, immediately north of the White House, to help address security concerns. Richard H. Macauley, the chief of the Uniformed Division of the Secret Service, confirmed that the temporary fencing has blocked off the park for at least six months because of construction and heightened security threats. Pam Fessler, a Washington resident, said she feared that the park would be shut down more often ahead of protests and gatherings if a permanent fence was installed. Mr. Paoletta downplayed those concerns.