WASHINGTON—The U.S. is urging Beijing to fill in the details of a slew of trade and investment proposals Chinese officials have made recently, as the two sides try to resolve a trade battle that has rocked global markets.

Since President Trump and Chinese President Xi Jinping met in Buenos Aires on Dec. 1, Beijing has pledged to cut tariffs, buy more U.S. goods and services, ease restrictions on foreign companies operating in China and further open sectors for foreign investment.

But...