WASHINGTON — Defense Secretary Jim Mattis announced Tuesday that he is freezing the implementation of President Trump’s ban on transgender people serving in the military, saying that he will first establish a panel of experts to provide advice and recommendations on how to carry out Trump’s directive.

The Pentagon confirmed the move in a statement attributed to Mattis, saying that the Pentagon will first develop a study and implementation plan “as directed” by the president in a memorandum released Friday. Soon-to-be arriving political appointees at the Defense Department “will play an important role in this effort,” the statement added. The plan will address both the potential for transgender people looking to serve in the military for the first time, and transgender troops who already are serving.

“Our focus must always be on what is best for the military’s combat effectiveness leading to victory on the battlefield,” Mattis said. “To that end, I will establish a panel of experts serving within the Departments of Defense and Homeland Security to provide advice and recommendations on the implementation of the president’s direction.”

Mattis added that panel members “will bring mature experience, most notably in combat and deployed operations, and seasoned judgment to this task.” The panel will “assemble and thoroughly analyze all pertinent data, quantifiable and non-quantifiable.”

The Pentagon chief said that after the panel makes its recommendations and he consults with the secretary of homeland security, he will provide his advice to Trump. In the meantime, policy regarding transgender service members will remain in place, Mattis said, meaning that those serving can continue to do so.

On Friday evening, the White House announced that it was moving forward with Trump’s transgender ban as Hurricane Harvey roared toward Texas. Trump said in a memorandum that he wanted the Pentagon “to return to the longstanding policy and practice on military service by transgender individuals that was in place prior to June 2016 until such time as a sufficient basis exists” to conclude that allowing them to service will not have negative effects.

The memorandum gave Mattis until February 1 to present a plan to Trump on how to implement the transgender ban, and what to do with transgender service members already serving. Those marked some of the first details the White House provided on how to carry out Trump’s decision, which initially took many Pentagon officials by surprise when the president announced it on Twitter on July 26.

“After consultation with my Generals and military experts, please be advised that the United States Government will not accept or allow Transgender individuals to serve in any capacity in the U.S. Military,” he said in three successive tweets. “Our military must be focused on decisive and overwhelming victory and cannot be burdened with the tremendous medical costs and disruption that transgender in the military would entail. Thank you.”

Gen. Joseph Dunford Jr., the chairman of the Joint Chiefs of Staff, added the following day that transgender service members already serving will be treated with dignity and respect as the Pentagon sorts out its new policy, but that it would carry out Trump’s directive.

Mattis had left the door open to some transgender service members continuing to serve during an exchange with reporters at the Pentagon. The defense secretary, asked Aug. 14 if current service members would be ousted, pointed to Dunford’s directive.

“The chairman immediately went out and said immediately, ‘Everyone stand fast until we get the direction,’ ” Mattis said. “I understand that this is probably more about your suspicion about what could be coming, but the fact is we have received no direction that would indicate any harm to anybody right now.”

The Obama administration repealed its ban on transgender service member serving in July 2016. A Rand Corp. study commissioned by the Pentagon found that there were between 2,500 and 7,000 transgender people among the 1.3 million on active duty, but Mattis has questioned whether the study is accurate.

Trump’s ban has prompted lawsuits that challenge its constitutionality and rebukes from Democrats in Congress.

“There is no place for discrimination in our Armed Forces or indeed anywhere else in American society,” 143 House Democrats said in a letter Tuesday. “Enforcing your ban could mean discharging active duty soldiers, sailors, Marines, and members of the Air Force who are serving honorably. It also would mean barring other patriotic Americans from serving in the future.”