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. One commissioner suggested the administration look into installing solar panels on the roof of the center. Another asked whether there would be an area for cars to pull over to drop people off, or whether vehicles would have to stop in the middle of the street.

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. The park is frequented by tourists and protesters because of its proximity to the White House.

According to the proposal, the fencing would not interfere with public access or impede peaceful demonstrations at the park. But law enforcement officials who spoke on Thursday in support of the fencing faced questions about why, then, temporary fencing around the park had closed it to the public.

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. He cited a shooting in May in the vicinity of the White House, as well as the Black Lives Matter protests of 2020, to support the need for a permanent fence.

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.

“What we are really doing is putting another barrier between Americans and their government,” Ms. Fessler said.

Mr. Paoletta downplayed those concerns. “This idea that if there’s a fence up, we’re losing our First Amendment rights,” he said, “I don’t accept.”

The panel, which has no enforcement power, is stacked with allies of Mr. Trump. Will Scharf, a former personal lawyer to Mr. Trump, oversaw the panel when it approved the ballroom construction. He resigned from the planning commission last week after being elevated to the position of White House counsel. His replacement, Mr. Paoletta, noted on Thursday that he serves as a lawyer for the Trump administration in four other positions across the federal government.

The panel is also reviewing Mr. Trump’s proposal to paint white the granite exterior of the Eisenhower Executive Office Building, which sits next door to the White House. The public comments from May mostly opposed that plan.

In another standoff on Thursday, a federal judge refused to interfere with the Trump administration’s cutting down around 150 trees in East Potomac Park, where Mr. Trump hopes to build a luxury golf course. Locals have organized to try to stop the administration from razing the park to make way for Mr. Trump’s proposed course.

Minho Kim contributed reporting.