NEW YORK TIMES

President Trump has directed his administration to more aggressively enforce the nation’s immigration laws, unleashing the full force of the federal government to find, arrest and deport those in the country illegally, regardless of whether they have committed serious crimes.

Documents released on Tuesday by the Department of Homeland Security revealed the broad scope of the president’s ambitions: to publicize crimes by immigrants; enlist local police officers as enforcers; strip immigrants of privacy rights; erect new detention facilities; discourage asylum seekers; and, ultimately, speed up deportations.

The new enforcement policies put into practice the fearful speech that Mr. Trump offered on the campaign trail, vastly expanding the definition of “criminal aliens” and warning that such unauthorized immigrants “routinely victimize Americans,” disregard the “rule of law and pose a threat” to people in communities across the United States.

Despite Mr. Trump’s talk, research shows lower levels of crime among immigrants than among native-born Americans.

But taken together, the new policies are a rejection of the sometimes more restrained efforts by former Presidents Barack Obama and George W. Bush and their predecessors, who sought to balance protecting the nation’s borders with fiscal, logistical and humanitarian limits on the exercise of laws passed by Congress.

“The faithful execution of our immigration laws is best achieved by using all these statutory authorities to the greatest extent practicable,” John F. Kelly, the secretary of homeland security, wrote in one of two memorandums released on Tuesday. “Accordingly, department personnel shall make full use of these authorities.”

The immediate impact of that shift is not yet fully known. Advocates for immigrants warned on Tuesday that the new border control and enforcement directives would create an atmosphere of fear that was likely to drive those in the country illegally deeper into the shadows.

Administration officials said some of the new policies — like one seeking to send unauthorized border crossers from Central America to Mexico while they await deportation hearings — could take months to put in effect and might be limited in scope.

For now, so-called Dreamers, who were brought to the United States as young children, will not be targeted unless they commit crimes.

Mr. Trump has not yet said where he will get the billions of dollars needed to pay for thousands of new border control agents, a network of detention facilities to detain unauthorized immigrants and a wall along the entire southern border with Mexico.

But politically, Mr. Kelly’s actions on Tuesday serve to reinforce the president’s standing among a core constituency — those who blame unauthorized immigrants for taking jobs away from citizens, committing heinous crimes and being a financial burden on federal, state and local governments.

And because of the changes, millions of immigrants in the country illegally now face a far greater likelihood of being discovered, processed and deported.

“The message is: The immigration law is back in business,” said Mark Krikorian, the executive director of the Center for Immigration Studies, a research center that supports restricted immigration. “That violating immigration law is no longer a secondary offense.”

Sean Spicer, the White House press secretary, said on Tuesday that the president wanted to “take the shackles off” of the nation’s immigration enforcers. But he insisted that the new policies were focused on making it clear that “the No. 1 priority is that people who pose a threat to our country are immediately dealt with.”

That was already the policy under the Obama administration, which instructed agents that undocumented immigrants convicted of serious crimes were the priority for deportation. Now, immigration agents, customs officers and border patrol agents have been directed to remove anyone in the country illegally.

“Under this executive order, ICE will not exempt classes or categories of removal aliens from potential enforcement,” a fact sheet released by the Department of Homeland Security said, using the acronym for Immigration and Customs Enforcement. “All of those present in violation of the immigration laws may be subject to immigration arrest, detention, and, if found removable by final order, removal from the United States.”

That includes people convicted of fraud in any official matter before a governmental agency and people who “have abused any program related to receipt of public benefits.”

The policy also calls for an expansion of expedited removals, allowing Border Patrol and Immigration and Customs Enforcement agents to immediately deport more people. Under the Obama administration, expedited removal was used only within 100 miles of the border for people who had been in the country no more than 14 days. Now it will include all those who have been in the country for up to two years, no matter where.

The change in enforcement priorities will require a considerable increase in resources. With an estimated 11 million people in the country illegally, the government has long had to set narrower priorities, given the constraints on staffing and money.

In the so-called guidance documents released on Tuesday, the department is directed to begin the process of hiring 10,000 immigration and customs agents, expanding the number of detention facilities and creating an office within Immigration and Customs Enforcement to help families of those killed by undocumented immigrants. Mr. Trump had some of those relatives address his rallies during the campaign, and several were present when he signed an executive order on immigration last month at the Department of Homeland Security.

The directives would also instruct Immigration and Customs Enforcement, as well as Customs and Border Protection, the parent agency of the Border Patrol, to begin reviving a program that recruits local police officers and sheriff’s deputies to help with deportation, effectively making them de facto immigration agents. The effort, called the 287(g) program, was scaled back during the Obama administration.

The program faces resistance from many states and dozens of so-called sanctuary cities, which have refused to allow their law enforcement workers to help round up undocumented individuals.

Under the new directives, the agency would no longer provide privacy protections to people who are not American citizens or green card holders. A policy established in the last days of the Bush administration in January 2009 provided some legal protection for information collected on nonresidents.

Immigration advocates say that could open the door to agents from the Department of Homeland Security getting medical, legal or other information about undocumented immigrants.

“It basically breaks down any protections immigrants have for seeking help in any way,” said Justin Mazzola, deputy director of research at Amnesty International in New York. “Under this, it seems that information that New York City collects for its undocumented immigrant ID card program would be available for disclosure.”

The new policies also target unauthorized immigrants who seek to smuggle their children into the country, as has happened frequently with Central American children seeking to reunite with parents living in the United States. Under the new directives, such parents could face deportation or prosecution for smuggling or human trafficking.

Senior homeland security officials told reporters on Tuesday morning that the directives were intended to make full use of the enforcement tools that Congress has already given to the department to crack down on illegal immigration. The officials, speaking on the condition of anonymity during a morning conference call, emphasized that some of the proposals for increased enforcement would roll out slowly as the department finalizes the logistics and legal rules for more aggressive action.

In particular, the officials said that returning Central American refugees to Mexico to await hearings would be done only in a limited fashion, and only after discussions with the government of Mexico, which would most likely have to agree to accept the refugees.

The officials also made clear that nothing in the directives would change the program known as Deferred Action for Childhood Arrivals, which provides work permits and deportation protection for the young people commonly referred to as Dreamers.

But the officials also made clear that the department intended to aggressively follow Mr. Trump’s promise that immigration laws be enforced to the maximum extent possible, marking a significant departure from the procedures in place under Mr. Obama.

That promise has generated fear and anger among immigrants across the country, and their advocates have warned that the new approach is a threat to many undocumented immigrants who had previously been in little danger of being deported.