“We’re putting the trade war on hold,” Mr. Mnuchin said on “Fox News Sunday.”

The reprieve came as many crucial details remained undecided, and trade experts warned that the suspension of tariffs could undercut Mr. Trump’s leverage and thrust the United States back into the kind of lengthy — and ultimately fruitless — negotiations with China that have bogged down previous administrations.

There are also large and lingering questions about what the United States planned to do with one of its most powerful bargaining chips: the Chinese telecom firm ZTE, which has been crippled by sanctions that prevent it from buying American components. Mr. Trump last week suggested on Twitter that he might rethink the company’s punishment in return for trade concessions.