WASHINGTON—The Trump administration plans to request $2 billion in new funding for border-wall construction, significantly less than the amount it sought last year, in the budget proposal set for release Monday, according to White House officials familiar with the planning.

The smaller proposal, the officials said, reflects the fact that the administration needs fewer resources to build a wall along the U.S. southern border, as it has essentially met its funding goals by shifting money from the military toward construction....