WASHINGTON — President Trump told President Xi Jinping of China on Thursday evening that the United States would honor the “One China” policy, reversing his earlier expressions of doubt about the longtime diplomatic understanding and removing a major source of tension between the United States and China since shortly after he was elected.

In a statement, the White House said Mr. Trump and Mr. Xi “discussed numerous topics, and President Trump agreed, at the request of President Xi, to honor our One China policy.” It described the call as “extremely cordial” and said the leaders had invited each other to visit.

The concession was clearly designed to put an end to an extended chill in the relationship between China and the United States. Mr. Xi, stung by Mr. Trump’s unorthodox telephone call with the president of Taiwan in December and his subsequent assertion that the United States might no longer abide by the One China policy, had not spoken to Mr. Trump since Nov. 14, the week after he was elected.

Administration officials concluded that Mr. Xi would take a call only if Mr. Trump publicly committed to upholding the 44-year-old policy, under which the United States recognized a single Chinese government in Beijing and severed its diplomatic ties with Taiwan.