A top Senate official on Friday night rejected a bid by Republicans to slash federal food aid payments as part of their sweeping legislation carrying President Trump’s domestic agenda, sending party leaders scrambling to find another way to help offset the massive cost of the bill.

The measure passed by the House last month and on track to be considered in the Senate next week would cover part of the cost of extending and expanding large tax cuts by cutting social safety net programs including Medicaid and nutrition programs, including SNAP, formerly known as food stamps.

Republicans are moving the bill through Congress using special rules that shield it from a filibuster, depriving Democrats of the ability to block it. But to qualify for that protection, the legislation must comply with a rigorous set of budgetary restrictions meant to ensure that it will not add to the deficit. And the Senate parliamentarian, an official appointed by the chamber’s leaders to enforce its rules and precedents, must evaluate such measures to ensure that every provision meets those requirements.

Elizabeth MacDonough, the parliamentarian, ruled that the SNAP measure, which would push some of the costs of nutrition assistance onto the states, did not. That sent Republicans back to the drawing board to find another strategy for covering tens of billions of dollars of the bill’s cost.

She also said Republicans could not include a provision that would bar immigrants who are not citizens or lawful permanent residents from receiving SNAP benefits, according to Senator Jeff Merkley of Oregon, the top Democrat on the Budget Committee.

The House-passed bill would require all states to pay at least 5 percent of SNAP benefit costs, and more if they reported a high rate of errors in underpaying or overpaying recipients. That provision was estimated to save roughly $128 billion.