Most economists in a recent survey view a trade war between the U.S. and China as the biggest threat to the U.S. economy in 2019, a sign that forecasters view political uncertainty and the potential for new punitive tariff barriers as greater risks than macroeconomic or financial disruptions.

Nearly half of economists who responded to a survey by The Wall Street Journal, 47.3%, said they viewed the U.S. dispute with Beijing as the No. 1 risk for 2019. Some 20% cited financial market disruptions and 12.7% pointed to a slowdown...