President Trump said on Sunday that the Boeing luxury jet donated by Qatar that he recently took overseas would soon be “maxed out,” suggesting it could get additional defensive capabilities to match the standards of the older jets used for presidential travel.

The president commented after returning to Washington from New Jersey aboard the jet, a Boeing 747-800 that was given as a gift — and which Mr. Trump has said he plans to take with him for his presidential library when he leaves office.

A reporter traveling with the small group of reporters in the presidential motorcade pointed to the Qatari jet’s fuselage and said: “Mr. President, this plane does not have antimissile defense systems on it. Why are you flying it?”

Mr. Trump replied, “Well, it has — it has a lot, and you know it has a lot of capability, but as I understand it, in about a month or so, they’re going to send it to have it be maxed out. So they’re going to be sending it, and they’ll have it be maxed out.

”It’ll take about a month,” he said.

It was not clear what specific upgrades Mr. Trump was referring to, or whether the time frame he gave of a month until it is ready was realistic. A White House spokesman did not immediately respond to an email seeking additional clarification of what Mr. Trump was referring to by “maxed out” and about the time frame he mentioned.

Nonetheless, it appeared to be an admission from the president that the plane’s security measures are not as extensive as the models that have been designed to be built from the ground up to serve as Air Force One.

The New York Times reported earlier this month that the new jet, which he flew to Turkey, lacks the same defensive countermeasures as the older model, including antimissile capabilities. The coverage prompted a leak investigation that included the highly unusual step of the F.B.I., just 24 hours after the story appeared, hand-delivering subpoenas to Times reporters to testify before a federal grand jury.

The Qatari-donated jet, a roughly 14-year-old plane, went through a costly yet relatively rushed process to make it safe to serve as Air Force One, the military call sign for whatever plane the president is flying.

The models that are built by Boeing for use by a U.S. president are intended to be a flying Oval Office, with antimissile defenses and a hardening of the plane’s wiring to protect it from an electromagnetic pulse in case there is a nuclear strike. The planes can also refuel in midair and contain a medical suite that can treat the president.

Mr. Trump flew the plane to Turkey for the NATO summit almost two weeks ago.

But he announced he was taking one of the older jets — which he has repeatedly criticized as too dated and stiff in its appointments — when he flew out of Turkey. The Times reported that the Secret Service had advised him to take the older plane.

The Times then reported that the donated aircraft, which administration officials describe as a “bridge” plane until the long-delayed two brand-new jets that the government has commissioned from Boeing arrive, is lacking some of the most sophisticated systems that the older Air Force One planes have.

The White House directed the F.B.I. director to oversee an investigation into how The Times obtained the information. That resulted in the subpoenas being served to several reporters involved in the coverage, with federal agents showing up at their homes to hand-deliver them, as opposed to sending the subpoenas to the newspaper’s lawyers.