But during a surprise trip to Iraq last week, Mr. Trump privately told the commander of American forces in Iraq and Syria, Lt. Gen. Paul J. LaCamera, that the military could have several months to complete a safe and orderly withdrawal, according to two United States officials. And on Sunday, Senator Lindsey Graham, Republican of South Carolina, told reporters that a “pause situation” on the troop withdrawal was in effect.

A Pentagon spokesman, Cmdr. Sean Robertson, said on Monday, “I’ll let the president’s words speak for themselves.”

By extending the timetable for withdrawal to several months, Mr. Trump stuck to his commitment to untangle the United States from yearslong military commitments but also heeded warnings from current and former military leaders of the danger of a quick exit. Defense Secretary Jim Mattis, who resigned in protest over Mr. Trump’s decision, said that leaving Syria in 30 days would jeopardize the fight against the Islamic State, betray its Syrian Kurdish-Arab allies on the ground, and cede the eastern part of the country to the Syrian government and its Russian and Iranian allies.

Nevertheless, Mr. Trump’s latest plan left open the question of whether an orderly pullout from Syria would happen. Military planners say they need about 120 days, or four months, to carry out a withdrawal that allows time to decide which equipment to move elsewhere in the region, leave behind with allies or disable to prevent it from falling into the hands of the Syrian government or Russia or Iran.

Military officials have declined to specify the timing of the departure, partly for operational security reasons and partly because many details are still quite fluid, and officials recognize that Mr. Trump could change his mind at any moment and speed up the departure.