Stocks in the United States fell sharply on Thursday after reports that Mr. Trump and Mr. Xi would not meet. Investors have been anxiously awaiting the end of the monthslong trade dispute between the world’s two largest economies. The Dow Jones industrial average declined 220.77 points, or 0.87 percent, while the Standard & Poor 500-stock index fell 25.56 points, or 0.94 percent.

While Mr. Trump’s negotiators previously sought to play down expectations that a deal could be reached by March 2, trade analysts and China experts viewed the lack of a formal meeting between the two leaders as a bad sign. It could also come as a surprise to the Chinese, given Mr. Trump’s friendly public meeting last week in the Oval Office with Liu He, China’s vice premier and top trade negotiator, who spent two days in discussions with Mr. Lighthizer and Steven Mnuchin, the Treasury secretary.

“This on-again, off-again meeting signals the enormous obstacles that still stand in the way of the two sides reaching even a partial deal by the early March deadline,” said Eswar Prasad, the former head of the International Monetary Fund’s China division.

“Trump’s conciliatory statements during Liu He’s recent visit to Washington generated a brief surge of optimism about prospects for a deal, but that has now dissipated as Trump and his administration again harden their public stance against China,” he said.

Discussions are still continuing, and Mr. Lighthizer and Mr. Mnuchin will lead an American delegation to Beijing next week for more trade negotiations.

Mr. Lighthizer briefed senators about the state of the negotiations on Wednesday. According to a congressional aide, Mr. Lighthizer was unable to offer specifics about how a deal with China would be enforced, including the administration’s demand that the Chinese stop forcing American companies to hand over technology as a condition of doing business there. Senators told Mr. Lighthizer that they wanted the text of any agreement or memo of understanding with China to be made public.

Thus far, there is no text or document that is serving as a draft of the agreement.

Trump administration officials have offered mixed signals and cautious optimism about how the negotiations have been going.