As its trade negotiators rushed to Washington to seek a reprieve from President Donald J. Trump’s blanket tariffs, South Korea on Wednesday announced new measures to soften the blow of levies on the country’s carmakers.

The two efforts underlined the delicate balance that South Korea needs to strike after the country, one of the most loyal U.S. allies in Asia, was hit by some of the heaviest tariff rates announced by President Trump last week.

Mr. Trump on Tuesday cheered the imminent arrival of the negotiating team from South Korea, which is led by Trade Minister Cheong In-kyo.

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The European Union plans to vote on Wednesday afternoon on its first retaliation measures in response to President Trump’s tariffs, moving closer to placing increased duties on a range of manufactured goods and farm products that would take effect in phases starting next week.

The list up for consideration is a slightly trimmed down version of one that was announced in mid-March in response to Mr. Trump’s steel and aluminum tariffs. E.U. officials have spent recent weeks consulting with policymakers and industries from across the 27-nation bloc in an effort to minimize how much the countermeasures would harm Europeans.

The final list is expected to exclude bourbon, for instance, after Mr. Trump threatened to place a 200 percent tariff on all European alcohol in response to its inclusion. That would have been a crushing blow for wine producers in France, Italy and Spain.

“We are not in a business of going, let’s say, cent for cent, or tit for tat, or dollar for dollar,” Maros Sefcovic, the bloc’s trade commissioner, said this week.

Since last month, the United States has introduced tariffs of 25 percent on steel, aluminum and cars, and broad 20 percent on everything else coming from Europe — and those broad-based tariffs took effect on Wednesday. European Union officials have said they would prefer to negotiate to get rid of those higher levies, and have even offered to cut tariffs to zero on cars and other industrial products if the United States does the same.

But with serious negotiations slow to materialize, Europe is striking back in a staggered way. The retaliatory tariffs up for a vote on Wednesday would be a first step, in response only to steel and aluminum levies.

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