WASHINGTON — The House pressed forward on Tuesday with plans to vote on an emergency $4.5 billion humanitarian aid bill to address the plight of migrants at the border, as Democratic leaders worked to quell a rebellion in their ranks over the measure by adding new health and safety requirements for children and adults held by the government.
Top House Democrats expressed confidence that they would have the votes to push through the measure, despite the concerns of a group of liberals and Hispanic-American lawmakers who have threatened to withhold their backing because they fear that the aid package would enable President Trump’s immigration crackdown.
“The overwhelming majority of House Democrats, including the overwhelming majority of the Progressive Caucus, will support this legislation, because we understand the urgency of the moment,” Representative Hakeem Jeffries of New York, the chairman of the Democratic caucus, told reporters on Monday. “This week, we have to resolve the humanitarian crisis.”
But the vote remained in doubt. Some Democrats in the party’s liberal wing, increasingly willing to wield their power, have said they will not vote to send one cent to the agencies that have carried out the president’s harsh policies, even with strings attached to rein in those policies and even if the package is intended to help vulnerable women and children living in badly overcrowded, squalid shelters.
“I am not planning on voting as it is,” said Representative Ilhan Omar, Democrat of Minnesota. “We have a humanitarian crisis, and what we are trying to do does not match that crisis.”
During a closed-door meeting of House Democrats at their campaign headquarters near the Capitol on Tuesday morning, Speaker Nancy Pelosi made an impassioned plea for her rank and file to support the bill, arguing that it would send a signal to the world that Democrats want to help suffering children at the border, according to a senior Democratic aide who described her private remarks on the condition of anonymity. Ms. Pelosi also warned that allowing their divisions over the measure to sink it would play into the president’s hands.
“The president would love for this bill to go down today,” Ms. Pelosi told Democrats, according to the aide. “A vote against this bill is a vote for Donald Trump and his inhumane, outside-the-circle-of-civilized attitude toward the children.”
Then the speaker, who is well known for her flair for tamping down internal rebellions in her ranks, asked a room packed with Democrats whether anyone had a problem with the legislation. Nobody spoke up, the aide said. She concluded the session by saying she expected “very few noes” and urging those thinking of opposing the bill to bring their questions to her and other House leaders.
Later, she repeated to reporters a point she had made to lawmakers behind closed doors, saying that the bill was a spending measure, not a policy plan.
“This isn’t an immigration bill,” Ms. Pelosi said. “It’s an appropriations bill to meet the needs of the children.”
Critics of the package huddled with Ms. Pelosi in her Capitol office on Monday night to air their complaints, and some emerged saying changes would be needed to garner their support. Leaders met into the night to discuss those modifications and came up with a handful that they plan to add to the bill before it reaches the floor on Tuesday afternoon.
Democrats plan to add language that would require Customs and Border Protection to establish plans and protocols to deliver medical care, improve nutrition and hygiene, and train personnel to ensure the health and safety of children and adults in custody. Another new provision would require the secretary of health and human services to specify which requirements are being temporarily waived to deal with a sudden influx of migrants. That amendment would limit the detention-center stay of any unaccompanied child to 90 days unless written notification is submitted to Congress attesting that no other facilities are available.
Democrats also intended to add new requirements for translators at Customs and Border Protection, Immigration and Customs Enforcement, and Citizenship and Immigration Services.
The White House has already threatened that Mr. Trump would veto the House bill because of restrictions that were included even before those new measures.
Senate Republicans and Democrats came together last week to draft a $4.6 billion version of the humanitarian aid package that also includes limitations on the use of the funds and several other conditions.
With House Republicans almost uniformly opposed to the stricter House measure, the fate of the entire effort remains uncertain. If the changes Ms. Pelosi settled on win over enough Democrats to push the package through the House on Tuesday afternoon, it would still have to be reconciled with the Senate’s bill before being sent to Mr. Trump for his signature.
Ms. Pelosi has argued that in order to give the House leverage in any such negotiation with the Senate, Democrats have to show the broadest possible support for the bill. Some lawmakers said the changes that leaders had agreed to over the last 24 hours persuaded them to support the measure.
“I was on the fence, but that makes me feel much better, so I’m leaning to supporting it,” said Representative Debbie Mucarsel-Powell, Democrat of Florida. “For me, specifically, it was the time frame that we had to set for reunification.”
Lawmakers from districts along the border have been among the strongest proponents of the bill, arguing that Democrats must put aside their antipathy for Mr. Trump’s immigration policies and focus on alleviating a humanitarian debacle.
“There are legitimate concerns about trust with the administration, and there is a legitimate fear that we are funding a dysfunctional system,” said Representative Veronica Escobar, Democrat of Texas, whose El Paso district abuts the border. “But we have to meet our obligations as human beings and fund the needs for the care of these children.”