President Trump promised during his presidential campaign to withdraw American troops from Syria, and has been looking for a way out since.CreditCreditSarah Silbiger/The New York Times

WASHINGTON — President Trump is considering pulling 2,000 United States ground troops out of Syria in a move that would seek to describe the four-year American-led war against the Islamic State as largely won, officials said Wednesday.

“We have defeated ISIS in Syria, my only reason for being there during the Trump Presidency,” the president said in a Twitter post on Wednesday morning. He offered no details on his plans for the military mission in Syria.

Sarah Huckabee Sanders, the White House press secretary, said in a statement that “we have started returning United States troops home as we transition to the next phase of this campaign.” It was not clear if that was part of a full withdrawal of American forces from Syria, as the Trump administration is debating.

But Pentagon officials were still trying to talk the president out of the decision early Wednesday morning, arguing that such a move would betray Kurdish allies who have fought alongside American troops in Syria and who could find themselves under attack in a military offensive now threatened by Turkey.

”At this time, we continue to work by, with and through our partners in the region,” Col. Rob Manning, a Pentagon spokesman, said in a short statement on Wednesday morning.

One official said the withdrawal of troops would be phased out over several weeks and that the American-led airstrike campaign against the Islamic State in Syria, which began in 2014, would continue. That official said the military hoped to rely on Kurdish fighters on the ground to help with targeting.

In a series of meetings and conference calls over the past several days, Defense Secretary Jim Mattis and other senior national security officials have tried to dissuade Mr. Trump from a wholesale troop withdrawal, arguing that such a significant national security policy shift would essentially cede foreign influence in Syria to Russia and Iran at a time when American policy calls for challenging both countries.

Abandoning the American-backed Kurdish allies, Pentagon officials have argued, will hamper future efforts by the United States to gain the trust of local fighters, from Afghanistan to Yemen to Somalia.

In addition, the Islamic State has not been full vanquished from the small territory it controls on the Syrian-Iraqi border. The Islamic State has held that territory for more than a year in the face of attacks by American-allied forces, and has used it as a launching pad to carry out attacks in Iraq and Syria.

But Mr. Trump promised during his presidential campaign to withdraw American troops from Syria, and has been looking for a way out since. He reluctantly agreed in April to give the Defense Department more time to finish the mission.

In recent days, President Recep Tayyip Erdogan of Turkey has given Mr. Trump just such a possible path: Mr. Erdogan has vowed to launch a new offensive against the Kurdish troops that the United States has equipped to fight the Islamic State in Iraq and Syria.

As the debate over withdrawing from Syria was raging inside the White House over recent days, Mr. Trump argued that the risk of a Turkish incursion could be a threat to the United States forces in Syria, officials said, although Mr. Erdogan would likely face huge reprisals if Turkish troops killed or wounded any Americans.

One possibility under discussion, officials said, was a phased withdrawal of American troops. But Mr. Trump, the officials said, seems to prefer pulling out all forces as soon as possible.

Some details of the administration debate on Syria were first reported early Wednesday by The Wall Street Journal.

On Monday, Mr. Erdogan said that he told Mr. Trump that Turkey would launch its offensive soon, and that he received positive assurances from Mr. Trump. But Turkish officials have said that before.

Turkey considers the American-backed Kurdish forces to be a terrorist group because of their connection to the Kurdistan Workers’ Party, a Kurdish insurgency in the region. The Syrian Kurds hope to create an autonomous region in northeast Syria, similar to the one in neighboring Iraq. They now control around 30 percent of Syria’s territory.

Pentagon officials have been pushing for a diplomatic solution to the issue.

The Islamic State, a militant group also known as ISIS, has lost an nearly all of its territory in Iraq and Syria, where the 2,000 American troops are mostly advising a militia made up of Kurdish and Arab soldiers.

In recent days, Turkey has accused the United States of failing to tackle security threats in the region. The United States and Turkey are NATO allies but uneasy partners in the war against the Islamic State.

But one Defense Department official suggested that Mr. Trump also wants to divert attention away from the series of legal challenges confronting him over the recent days: the Russian investigation run by the special counsel as well as the sentencing of his former personal lawyer, Michael Cohen, in a hush-money scandal to buy the silence of two women who said they had affairs with Mr. Trump.

Mr. Trump’s former national security adviser, Michael T. Flynn, was in court on Tuesday, where he was harshly criticized by federal judge for his efforts to mislead federal investigators.