Details emerged Friday from the U.S.’s first-stage trade deal with China, which marked a milestone in President Trump’s initiative to rebalance trade with Beijing but left questions over how far it goes to level the playing field for U.S. businesses.

The limited agreement, capping months of sometimes-testy negotiations, calls for China to purchase more products from American farmers and other exports, U.S. officials said. In return, the U.S. put the brakes on new tariffs set to take effect Sunday and agreed to reduce some...