“Industries that buy steel and aluminum, not to mention agricultural exporters, employ many times more people than the industries that the president wants to protect,” said Peter A. Petri, an economist and trade expert at Brandeis University’s International Business School. “Whether we go through with his approach is anyone’s guess, but business investment depends on predictable policy, and relentless chaos takes its toll even if cooler heads prevail on the policies that the president is tweeting about.”

The planned tariffs are stiff: 25 percent for steel and 10 percent for aluminum. They appear likely to buoy domestic investment and, to some degree, job creation in those industries, while raising prices on consumers and squeezing other industries that rely heavily on metals, such as automobile manufacturing and beverage production. They were hailed by labor groups, whose workers have seen their jobs shipped overseas, liberal economists and lawmakers, while criticized by business groups such as the National Retail Federation.

On their own, the tariffs appear unlikely to affect growth or inflation to a great degree, economists said. Mr. Trump’s tariffs “would by themselves have only a small macroeconomic impact,” said Mark Zandi, the chief economist at Moody’s Analytics and a vocal critic of Mr. Trump’s trade agenda during the campaign. Mr. Zandi said they were likely to add not quite 0.1 percentage points to inflation, which is currently hovering just under 2 percent, and to reduce economic growth by only a few hundredths of a percentage point.

What worries many economists, particularly on Wall Street, is the prospect that Mr. Trump is set to launch a broader trade war. The national security grounds he is invoking as rationale for the tariffs could provoke swift retaliation from trading partners such as Canada, which will be affected far more by the measures than China will.

“This is likely to escalate trade tensions,” economists at Goldman Sachs wrote on Thursday, “particularly as it looks likely to apply to a broad group of countries including to some allies of the U.S. We expect further disruptive trade developments over the coming months.”