WASHINGTON — The Trump administration unveiled a regulation on Wednesday that would allow it to detain indefinitely migrant families who cross the border illegally, replacing a decades-old court agreement that imposed a limit on how long the government could hold migrant children in custody and specified the level of care they must receive.
The White House has for more than a year pressed the Department of Homeland Security to replace the agreement, known as the Flores settlement, a shift that the administration says is crucial to halt immigration across the southwestern border.
The new regulation , which requires approval from a federal judge before it can go into effect and was expected to be immediately challenged in court, would establish standards for conditions in detention centers and specifically abolish a 20-day limit on detaining families in immigration jails, a cap that has prompted President Trump to repeatedly complain about the “catch and release” of families from Central America and elsewhere into the United States.
“This rule allows the federal government to enforce immigration laws as passed by Congress,” Kevin K. McAleenan, the acting secretary of homeland security, said in a statement. He called it a “critical rule” that would allow the government to detain families and maintain the “integrity of the immigration system.”
The administration proposed the rule last fall, allowing the public to comment on the potential regulation. It is scheduled to be published this week in the Federal Register and would take effect 60 days later, though administration officials concede that the expected court challenge will probably delay it.
Under the new rule, the administration would be free to send families who are caught crossing the border illegally to a family residential center to be held for as long as it takes for their immigration cases to be decided. Officials said families cases could be resolved within three months, though many could drag on much longer.
Trump administration officials — who briefed reporters on Tuesday night on the condition of anonymity to discuss the plans — said that many of the families would be detained until they were either released after being awarded asylum or they were deported to their home countries. Some families might be awarded parole to leave the facilities while the courts decide their fate.
The 20-day limit has been in place since 2015, a legal outgrowth of a 1997 court-ordered consent decree after a federal class-action lawsuit alleged physical and emotional harm done to immigrant children held for extended periods of time in the detention facilities.
Previous administrations tried to change the rules for detaining children in efforts to reduce surges of migrants crossing the border. Mr. Trump’s homeland security officials have repeatedly said that limiting the detentions of entire migrant families has driven the surge of Central American families who crossed the border this year.
The officials said on Tuesday that enacting the new regulation would send a powerful message that bringing children to the United States was not “a passport” to being released from detention.
They predicted that the rule would cause a significant decrease in the number of families trying to cross into the United States illegally, reducing the need for more family residential centers.
Withdrawing from the consent decree has also been a personal objective for Stephen Miller, the architect of Mr. Trump’s immigration policy. Delays in finishing the new regulation had prompted Mr. Miller to lash out at senior homeland security officials, who were ousted from the department.
The New York Times reported in April that Mr. Miller berated the former acting director of Immigration and Customs Enforcement, Ronald D. Vitiello, for not finishing the new rule. Mr. Vitiello later had his nomination withdrawn by Mr. Trump, who said he was not tough enough for the job.
The Flores settlement has also been at the root of partisan debates on immigration. Democrats have said the rules, are imperative to ensuring the well-being of detained children, especially after reports of children being kept in overcrowded cells and sometimes going without showers, toothpaste or hot meals.
Mr. McAleenan told the House Homeland Security Committee in May that the Flores settlement had incentivized migration to the United States, saying that “if an adult arrives with a child, they have a likelihood of staying in the United States.”
Representative Bennie Thompson, Democrat of Mississippi and the chairman of the committee, reminded Mr. McAleenan of the original purpose of the court-ordered regulations.
“It was about prolonged detention of children had proven to be harmful to their health,” Mr. Thompson said. “I think the court looked at it from that perspective rather than a punitive decision on the department.”
The Trump administration’s regulation, which is several hundred pages long, eliminates a requirement that federal detention centers for immigrant families be licensed by states, most of which had no such licenses.
Instead, under the regulation, the three centers built to house hundreds of immigrant families — in Dilley and Karnes City, Tex., and Leesport, Pa. — would have to meet standards set only by ICE, which runs them.
The administration officials insisted Tuesday that the facilities were, and would continue to be, maintained at high standards for the immigrants who were detained there. They said the facilities provided health care, education and “top notch” food.
But critics of the administration have long argued that the facilities were unsuitable for children to be held for long periods of time. And the recent examples of horrible conditions at overcrowded Border Patrol detention centers have underscored their concerns about the residential centers.
“We don’t disagree with detaining children when it’s necessary — namely, if they’re a flight risk or they’re a danger to themselves or others, we agree,” said Peter Schey, a lawyer who filed the original case and has continued to defend the settlement terms in court since. “It’s the unnecessary detention of child that this settlement sought to end. So these regulations really reflect a flagrant disregard on the part of President Trump and his administration for the safety and the well-being of children in the care of the federal government.”
Last summer, the Trump administration began separating children from their parents as a way to get around the Flores agreement. The children were sent to the custody of the Department of Health and Human Services while the adults were imprisoned while awaiting trial on their violation of immigration laws.
A fierce political backlash forced Mr. Trump to publicly abandon the separation policy, though immigration advocates said some families continued to be separated after that announcement.
Administration officials said Tuesday that the effort to allow families to be detained indefinitely was an attempt to avoid having to either separate families or release them while they waited for their cases to be heard.
Even before the final rule was announced on Wednesday, immigration advocates said it amounted to a cruel effort to imprison families — some with infants or young children — many of whom are fleeing violence and corruption in their home countries.
Under the terms of the 1997 consent decree, the regulation must be approved by the judge in the original case, Judge Dolly M. Gee of United States District Court for the Central District of California. The government will have seven days to file a brief in her court seeking her approval of the regulation.
If she refuses, the administration is expected to appeal her decision in a case that could drag on for months or even years, legal experts said.
Caitlin Dickerson contributed reporting from New York.