The Trump administration on Tuesday narrowed the list of Chinese products it plans to impose new Tariffs on as of Sept. 1, delaying levies on cellphones, laptop computers, toys and other goods to spare shoppers from higher prices during the back-to-school and holiday seasons.

The move, which pushed a new 10 percent tariff on some goods until Dec. 15 and excluded others entirely, came as President Trump faces mounting pressure from businesses and consumer groups over the harm they say the continuing trade war between the United States and China is doing.

But his announcement this month of the 10 percent tariff on $300 billion of Chinese goods meant consumers would soon feel the trade war’s sting more directly.

The stumbling blocks include whether Mr. Trump would roll back the 25 percent tariffs the administration has already imposed on roughly $250 billion of Chinese goods and whether Beijing would enshrine in law the reforms it has pledged to make.

The S&P 500 climbed nearly 2 percent after the announcement, lifted partly by stocks of retailers and computer chip producers that have been sensitive to indications that trade tensions were getting either better or worse.

Earlier Tuesday, Mr. Trump had criticized China for not making large purchases of American farm goods, suggesting that the tariffs might force them into action.