WASHINGTON — The Supplemental Nutrition Assistance Program offers about 46 million low-income Americans both sustenance and economic choice by providing an allowance to buy the fruit, meat, fresh vegetables, soda, ice cream and kind of bread they want to eat.

But on Monday, the Trump administration sprung a surprise: Under a proposal in the president’s budget many participants in the program would be given half their benefits in the form of a “Harvest Box” full of food preselected for nutritional value and economic benefit to American farmers. The cache of cheaper peanut butter, canned goods, pasta, cereal, “shelf stable” milk and other products would now be selected by the federal government, not by the people actually eating it.

The proposal seemed like a radical overhaul of the country’s core food assistance program — once called food stamps but now commonly known as SNAP. The idea was to shave about $21 billion a year from the federal deficit over the next 10 years. But the reaction was immediate, and largely negative.

Democrats claimed the plan shackled the poor while business groups, led by big food retailers, would stand to lose billions of dollars in lost SNAP business. The head of one trade association typically supportive of President Trump’s economic policies accused the administration of reneging on its pledge to cut “red tape and regulations.”