Defense Secretary Jim Mattis and other top national security officials argued that a withdrawal would, essentially, surrender Western influence in Syria to Russia and Iran. The Trump administration’s national security policy calls for challenging both countries, which are the chief benefactors of President Bashar al-Assad of Syria and have provided him with years of financial and military support.

Abandoning the Kurdish allies, the officials argued, also would cripple future American efforts to gain the trust of local fighters for counterterrorism operations, including in Afghanistan, Yemen and Somalia.

The Russian Foreign Ministry welcomed the move, according to the TASS news agency, saying that a withdrawal created prospects for a political settlement in Syria’s civil war. It also said an initiative to form a Syrian constitutional committee would have a bright future once American troops were gone.

While Mr. Trump has long cast American military involvement in Syria as narrowly focused on defeating the Islamic State, his generals and diplomats argue that the United States has broader, more complex interests there.

Gen. Joseph Votel, the commander of United States Central Command, and Brett H. McGurk, the American envoy to the coalition fighting the Islamic State, fiercely protested the military withdrawal, administration officials said. Both argued that the Islamic State would never have been defeated without the Kurdish fighters, whom General Votel said suffered many casualties and always lived up to their word.

Officials said General Votel argued that withdrawing American troops would leave the Kurds vulnerable to attack from Turkey, which has warned it will soon launch an offensive against them. It would also cement the survival of Mr. Assad, whose ouster had long been an article of faith in Washington.