WASHINGTON—With the U.S. and China preparing for a fresh round of face-to-face negotiations, President Trump said the U.S. expected to keep tariffs on Chinese goods in place for a “substantial period of time,” even after a deal.

“We have to make sure that if we do the deal with China that China lives by the deal,“ Mr. Trump told reporters as he left Washington for Ohio. Administration officials have talked of removing tariffs in stages, as Beijing shows that it has carried out parts of a deal—and reimposing them if China later...