The United States and China have agreed that an initial trade deal between the two countries would roll back a portion of the tariffs they are placing on each other’s products, officials from both countries said, a significant step toward defusing tensions between the world’s largest economies.

The agreement has not yet been completed, and a deal could fail to materialize as it has in previous rounds of negotiations. But if a pact is reached, the Trump administration has committed to cutting some tariffs, American officials and other people with knowledge of the negotiations said.

This is the first time the administration has agreed to remove any of the tariffs it has placed on $360 billion worth of Chinese goods. While President Trump canceled a planned tariff increase in October, he has routinely dangled the prospect of additional taxes if Beijing does not accede to America’s trade demands.

A deal that includes reversing even some tariffs creates a political dilemma for Mr. Trump, a self-avowed “tariff man” who has used levies to punish China for trade practices that have helped hollow out American manufacturing and to press Beijing to change its economic practices. But stock markets, which Mr. Trump sees as an economic barometer of his presidency, do not share his affinity for tariffs, and have been steadily rising with hope for a deal. Many businesses and farmers, which are struggling under the weight of the president’s trade war, are also eager for a deal.