But in a proclamation issued late Monday evening, Mr. Biden said the concerns that had fueled the tariffs in the first place still existed. “In my view, the available evidence indicates that imports from the U.A.E. may still displace domestic production, and thereby threaten to impair our national security,” Mr. Biden said.

Tom Conway, the president of the United Steelworkers International union, applauded the move, saying that Mr. Trump’s actions had constituted “a blatant attack on American workers.”

“Trump’s plan to lift tariffs on imports from the United Arab Emirates would undermine the effectiveness of the program and essentially exempt the vast majority of aluminum imports,” Mr. Conway said.

The United Arab Emirates is one of the world’s largest aluminum exporters, the result of an abundant petroleum supply that keeps the cost of the energy-intensive aluminum production process low. Between January and November of last year, it exported more aluminum to the United States than any other country except Canada.

American aluminum producers have struggled to compete with a surge in production from state-funded factories in countries like China, Russia and the United Arab Emirates, as well as growing aluminum production in countries with a lower cost of energy, like Canada. Because of various trade curbs, the United States imports a limited amount of aluminum directly from China, but China’s massive production still pushes down metal prices worldwide, making it harder for American businesses to compete.

The United States went from being the world’s top producer of aluminum two decades ago to to being surpassed by China, Russia, the U.A.E., Canada and other countries. It produced 741,000 metric tons of primary aluminum in 2017, the lowest level since 1951 and just 1.2 percent of the global supply.

But the tariffs have sparked an outcry from downstream American industries that use steel and aluminum to make products like cars, boats, recreational vehicles and cans. These producers say the tariffs have increased their costs, narrowing their profit margins and making it more difficult for their products to compete on the global market.

Some critics have also denounced the national security rationale for the tariffs, pointing out that the bulk of American aluminum imports come from Canada, a close military ally.