WASHINGTON — The Trump administration will make it harder for legal immigrants who rely on government benefit programs, such as food stamps and subsidized housing, to obtain permanent legal status as part of a far-reaching new policy aimed at altering the flow of legal immigration and reducing the number of poor immigrants.

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The move will have the greatest impact on immigrants who are living in the country legally and are likely to receive government benefits, making it much harder for people who are struggling financially to win legal permanent status — commonly known as a green card — so they can remain in the United States.

Kenneth T. Cuccinelli II, the director of United States Citizenship and Immigration Services, announced the new regulation at the White House on Monday morning, declaring that it would allow the government to insist that immigrants who come to the country were self-sufficient and would not be a drain on society.

“The benefit to taxpayers is a long-term benefit of seeking to ensure that our immigration system is bringing people to join us as American citizens, as legal permanent residents first, who can stand on their own two feet, who will not be reliant on the welfare system, especially in the age of the modern welfare state which is so expansive and expensive,” Mr. Cuccinelli said.

Under the new rule, the financial well-being of immigrants who are in the United States legally on temporary visas will be more heavily scrutinized when they seek a green card. Immigration officials will consider an immigrant’s age, health, family status, assets, resources, financial status and education. But the officials will be given broad leeway to determine whether an immigrant is likely to be a user of public benefits, to deny them a green card, and to order them deported out of the country.

© Anna Moneymaker/The New York Times President Trump boarded Air Force One last week. Officials said the program would not apply to people who already have green cards, to refugees and asylum-seekers, or to pregnant women and children. But immigration advocates warned that vast numbers of immigrants, including those not actually subject to the regulation, may drop out of needed benefits programs because they fear retribution by immigration authorities.

“This news is a cruel new step toward weaponizing programs that are intended to help people by making them, instead, a means of separating families and sending immigrants and communities of color one message: you are not welcome here,” said Marielena Hincapié, executive director of the National Immigration Law Center.

She added: “It will have a dire humanitarian impact, forcing some families to forgo critical lifesaving health care and nutrition. The damage will be felt for decades to come.”

Monday’s announcement is part of President Trump’s concerted assault on the nation’s system of immigration laws and regulations. For much of the past three years, the president has railed against what he calls the dangers of illegal immigration. But administration officials have also sought to impose new limits on legal immigration into the United States.

The rule has been the top priority of Stephen Miller, the architect of Mr. Trump’s immigration agenda, who views it as the most significant change to regulations that had encouraged migrants to come to the United States. Mr. Miller has repeatedly pushed administration officials to finish the regulation, known as the public charge rule, at one point telling colleagues that he wanted them to work on nothing other than it until it was completed.

L. Francis Cissna, the former director of Citizenship and Immigration Services, had resisted the rush to finish the rule, drafts of which were several hundred pages long and very complicated. But Mr. Cissna was forced out of his position earlier this year and replaced by Mr. Cuccinelli, a former attorney general in Virginia and an immigration hard-liner who shares Mr. Miller’s view that immigrants should not rely on financial support from the government.

The complex regulation, which is scheduled to go into effect in 60 days, would give the Trump administration a powerful new tool to narrow the demographic of people who come to live and work in the country. According to the new rule, the United States wants immigrants who can support themselves, not those who “depend on public resources to meet their needs.”

The ability of immigrants to support themselves has long been a consideration in whether they were granted the right to live and work in the United States permanently. But the Trump administration’s new move has made predicting the economic well-being of immigrants a more central part of that decision-making process.

An applicant who speaks English, shows formal letters of support and has private health insurance would be more likely to be approved than someone whose economic situation suggests they would probably need housing vouchers or enroll in Medicaid in the future if they were given a green card.

Over time, administration officials hope that the tough policy will shift the composition of the American immigration system by favoring wealthier immigrants.

Asked about the plaque on the Statue of Liberty that invites “your tired, your poor, your huddled masses,” Mr. Cuccinelli said that “I’m certainly not prepared to take anything down off the Statue of Liberty. We have a long history of being one of the most welcoming nations in the world.”

But immigration advocates reacted with anger at the announcement, calling it a cruel policy that they said was already causing immigrants around the country to abandon housing and medical benefits because they were concerned about the impact that using them might have on their immigration status or the status of someone in their family.

“Shame on the Trump administration for expanding a rule with racist roots in a shameful ploy to rig the immigration system for the wealthy,” said Cynthia Buiza, executive director of the California Immigrant Policy Center. “We thank all who stood up against the administration’s hate-filled agenda, and we will continue to fight for our values of community, compassion, and common humanity.”

The fear touched off by the new rule is illustrated by Maria, a 28-year-old woman from Colombia who is five months pregnant with a baby girl and reached out to her lawyer for advice a couple of weeks ago after she started seeing coverage of the draft version of the public charge rule in the news. Her husband, a childhood friend from Colombia, is a United States citizen, and she is in the United States on a tourist visa while she applies for a green card with him as a sponsor.

Maria’s husband, a high school teacher, had been off work during the summer break, forcing them to enroll in supplemental nutritional program for women, infants and children, known as WIC, in order to afford food and prenatal care. Though the new rule specifically does not penalize pregnant women for seeking such assistance, she said she fears that it could be used against her anyway. She said she wished she could stop accepting the help.

“I can’t,” said Maria, who worked as an industrial engineer in Colombia and asked that her last name not be used because she feared reprisals by American immigration officials. “Right now we need to use it,” she said, adding: “Whatever happens, the most important thing is that the baby is O.K., right?”

How many people the rule will affect is in dispute. Citizenship and Immigration Services did not conduct an “in-depth” analysis to estimate that, according to a senior administration official, who asked for anonymity to brief reporters on the rule.

But in the Federal Register, Homeland Security officials estimated that more than 382,000 immigrants seek an adjustment to their immigration status each year and would be subject to the public charge review. More than 324,000 people in households with undocumented immigrants are estimated to drop out or not enroll in public benefit programs.

Advocacy organizations say the number of people affected by the regulation is vastly larger, estimating that 26 million immigrants living in the United States legally will reconsider their use of public benefits because they fear how accepting assistance could affect their ability to remain in the United States.

Asked whether the agency expected immigrants to drop out of benefits they’re entitled to simply because of fear of losing their protections, the official said, “whether or not somebody disenrolls, you know, that’s a decision the alien would have to make to consider the future immigration consequences but the intention is not to have disenrollment consequences.”

Several immigration groups have pledged to sue the administration in an attempt to block the regulation from going into effect. Tens of thousands of people opposed the rule in a public comment period over the past several months.

The regulation was published in the Federal Register Monday morning with the following acknowledgment: “While some commenters provided support for the rule, the vast majority of commenters opposed the rule.”

Caitlin Dickerson and Zolan Kanno-Youngs contributed reporting.