The U.S. and China took an initial step to cement a trade agreement that had been derailed, with Washington saying on Friday it would shelve a planned increase in tariffs on goods imported from China, while Beijing would increase purchases of U.S. agricultural products.

The two sides left many details to be worked out in the weeks or months ahead on tough issues including China’s enforcement of intellectual property rules, U.S. access to Chinese markets, Chinese government support for state-owned enterprises, and the fate...