BRUSSELS—Negotiations with the Trump administration are testing European cohesion as the bloc inches toward a potential trade deal with the U.S. European Union officials are closing in on the outline of a deal that includes tough concessions for the bloc.

The EU is pushing to secure a preliminary deal before August 1 that would lock in a uniform 10% tariff rate while both sides work on a more comprehensive agreement. Without a deal, nearly all EU exports to the U.S. could face punitive tariffs of up to 50%.