President Trump’s new Air Force One, the Boeing luxury jet donated by Qatar, will be taken out of service for about one month this fall for “additional upgrades and enhancements,” the White House press secretary said on Monday.

The details about the additional work on the plane came a day after Mr. Trump appeared to acknowledge that the plane required more features, telling reporters that it would soon be “maxed out.” The plane has come under scrutiny over whether it is fitted with sufficient defensive capabilities.

“The new Air Force One is perfectly safe for the president’s travels, but will receive additional upgrades and enhancements in the fall which will take approximately one month to complete,” Karoline Leavitt, the press secretary, said in a statement. “During that time, the president will fly on the old Air Force One.”

Ms. Leavitt did not specify what upgrades would be made to the plane.

Mr. Trump flew the new aircraft earlier this month to the NATO summit in Turkey, but then changed planes when flying back. He used the old airplane to fly from Turkey to Britain, then switched to the Qatari jet again for the trip to the United States. The New York Times first reported that the change came at the request of the Secret Service, which raised concerns about the president flying on the new plane given the resumption of hostilities with Iran.

The Times then reported that the new jet lacks the same defensive countermeasures as the older model, including antimissile capabilities.

The coverage prompted a leak investigation; shortly after the stories published, the F.B.I. hand-delivered subpoenas to Times reporters to testify before a federal grand jury. The Trump administration has also sought the phone records of several Times journalists and their relatives in its effort to unmask the confidential sources who had provided information for articles about the security capabilities of the plane.

Mr. Trump had long complained about the old Air Force One and has been frustrated by the yearslong delay in readying two brand-new jets that the government has commissioned from Boeing. The Qatari-donated jet, a roughly 14-year-old plane, went through a costly yet relatively rushed process before Mr. Trump first flew on it earlier this month.

On Monday, the White House account on X referred to the planned upgrades as “planemaxxing,” internet slang for optimizing.