WASHINGTON — The Obama administration said on Monday that it would not seek Congressional approval of free trade agreements with Colombia, Panama and South Korea until Republicans agree to expand assistance for American workers who might lose jobs as a result.

President Obama has made the three deals a focus of his foreign and economic policy, but the Monday ultimatum reflects the political difficulty of advancing the deals in the face of high unemployment and opposition from parts of the Democratic base.

“This administration believes that just as we should be excited about the prospect of selling more of what we make around the world, we have to be equally firm about keeping faith with America’s workers,” said Ron Kirk, the United States trade representative.

The announcement puts the White House in line with Congressional Democrats who have made expanded benefits a condition of their support for the trade deals, and at loggerheads with Republicans who say the government cannot afford the cost.