The 15% tariff would be lower than previously threatened, but it would remain a high duty on America’s largest trading partner.

The pact would set duties of 15 percent on imports of items such as wine and automobiles, or about half the 30 percent the president had recently threatened.

Both sides hailed the agreement as the biggest ever. But it will come at a cost to the European Union, and many details have yet to be nailed down.