The Trump administration said Tuesday it would extend $12 billion in emergency aid to farmers amid signs the U.S. agricultural sector is beginning to feel the impact of President Donald Trump’s escalating trade disputes with major U.S. trading partners.

Agriculture Secretary Sonny Perdue said the U.S. government would provide incremental payments to support prices of some of the hardest-hit commodities, including soybeans, sorghum, cotton, corn, wheat and pork.

“This is a short-term solution that will give President Trump and his administration time to work on long-term trade deals,” Mr. Perdue told reporters. Agriculture Department officials said the aid wouldn’t need congressional approval.

Mr. Perdue said the move, tentatively planned for the coming months, was in response to what he called U.S. trading partners’ “illegal retaliation” to the policies of Mr. Trump, who has ordered tariffs on imports ranging from metals to materials to clothing to electronic parts. Those tariffs apply to goods from a broad range of countries, including China and those of the European Union.

U.S. trading partners are retaliating, with ominous implications for the American Farm Belt. China, a huge market for U.S. agricultural exports, has applied tariffs on $34 billion worth of U.S. goods, including soybeans and pork. Other places applying retaliatory tariffs include allies such as Canada, Mexico and the EU.

European Commission President Jean-Claude Juncker is scheduled to meet with Mr. Trump at the White House on Wednesday, and trade is expected to be high on the agenda. Mr. Juncker is expected to try to dissuade Mr. Trump from further escalation of trade fights, particularly over automobile imports to the U.S.

Congressional lawmakers, with few exceptions, expressed skepticism about the administration’s aid plan. Farmers, the critics said, need certainty on trade, not a bailout from the government. Even GOP senators who usually defend Mr. Trump expressed worry that aid might have to be extended to other sectors if he continues his trade fights on various fronts.

“What’s the strategy, what’s the end game here? At what point do we start seeing things move out of the chaotic state they are in now and to where we actually see new trade agreements?” asked Sen. Mike Rounds (R., S.D.).

Sen. Heidi Heitkamp (D., N.D.) said more aid might be needed if Mr. Trump continues imposing tariffs and other countries retaliate. “Twelve billion sounds like a lot of money, but we’re going to be losing literally hundreds of millions of dollars in every state” due to the trade disputes, she said.

Republican lawmakers from farm states said they expect to meet Wednesday afternoon with Mr. Trump, following his meetings with European officials. U.S. trading partners have targeted retaliatory tariffs on U.S. exports from rural communities, areas that supported Mr. Trump and Republicans in the 2016 election.