Treasury Secretary Janet L. Yellen plans to warn in a speech on Thursday that the economic policies being proposed by former President Donald J. Trump would fuel inflation and harm businesses, raising alarm about the risks of blanket tariffs.

The critique, which is set to be delivered in remarks to the Council on Foreign Relations, comes less than a month before the presidential election. Mr. Trump and Vice President Kamala Harris have outlined starkly different views about how they see America’s role in the global economy. Although Ms. Yellen is not expected to mention Mr. Trump by name, she will argue that the broad tariffs the former president and some Republicans in Congress support would damage the U.S. economy.

“Calls for walling America off with high tariffs on friends and competitors alike or by treating even our closest allies as transactional partners are deeply misguided,” Ms. Yellen plans to say in her speech, which was obtained by The New York Times. “Sweeping, untargeted tariffs would raise prices for American families and make our businesses less competitive.”

Mr. Trump imposed tariffs on hundreds of billions of dollars of foreign products during his presidency, but his plans if he is re-elected would dwarf those moves. On previous occasions, Mr. Trump suggested imposing tariffs of 10 to 20 percent on most foreign items, as well as a tariff of 60 percent or more on goods from China, in addition to other levies.