Secretary of State Rex W. Tillerson, administration officials said, was among those who urged Mr. Trump to publicly endorse the One China policy as a way to defuse tensions with Mr. Xi. Before Thursday, the two leaders had not spoken since Nov. 14; administration officials said that the Chinese leader would not get on the phone with Mr. Trump without assurances from the administration that he would commit to the policy.

Defense Secretary Jim Mattis has also emerged as an influential player, officials said. He recently returned from a trip to Asia during which he offered reassurances of American support for allies like Japan and South Korea. Among his travel companions was Matthew Pottinger, who recently became the senior director for Asia in the National Security Council.

“There finally is an administration beginning to take shape around him, which there was not before — Tillerson and Mattis in particular,” said Jeffrey A. Bader, a former top China adviser to Mr. Obama. “During the transition, no one had the nerve or expertise to contradict him.”

In addition to his cabinet officers, Mr. Trump and his aides are beginning to soak up advice from other leaders. The president stiffened his tone on settlements after he met briefly with King Abdullah II of Jordan; his advisers, including Jared Kushner, spoke with Arab officials, who urged the administration not to give Israel a free hand on the issue.