The tariffs rest on a little-used legal provision that allows Mr. Trump to restrict imports to try to bolster the American industrial base in the interest of national security. That power will face scrutiny by the World Trade Organization but, perhaps more significant, could prompt other countries to follow suit in using national security as a reason to wall off their markets.

American technology companies, agricultural producers and other industries could ultimately lose business abroad as nations seek to erect similar barriers.

Robert L. Shanks, Ford Motor’s chief financial officer, said commodities markets had already started to price in increases for steel and aluminum on the expectation that Mr. Trump would impose the tariffs. The effect on Ford, he said, is “not positive” given the automaker uses those metals in the cars they produce.

The European Union detailed a three-step plan to penalize $3.5 billion of American trade — the same amount of European steel and aluminum the bloc estimates would be harmed by the planned tariffs. It proposed taxing American exports including bourbon, bluejeans, orange juice, cranberries, rice and motorcycles. The European Union could then take action to protect their own metal makers from a surge in imports, and bring a case against the United States at the World Trade Organization.

A European Union official said that the bloc had been preparing for the announcement for months and that everything was in place for a swift, proportionate response.

The measures were intended to put pressure on politically sensitive areas, trade analysts said. Harley-Davidson motorcycles are made in the home district of Speaker Paul D. Ryan, Republican of Wisconsin. Orange juice comes from the swing state of Florida. Restrictions on Kentucky bourbon could add pressure on the Senate majority leader, Mitch McConnell, who is from the state.