While the practical effect of the measures could therefore be broad, legally they will be limited, providing only temporary reprieves from deportation. Congress could change the laws that Mr. Obama will rely on for his actions, and a future president could cancel the program, leaving immigrants out in the open and even more exposed to removal.
Mr. Obama said he had decided to take the measures after an immigration overhaul passed by the Senate died this year in the Republican-controlled House. His plans to act unilaterally have infuriated Republicans newly empowered in the midterm elections, who say they earned a chance at the polls to write their own immigration legislation in the Congress they will control next year.
The House speaker, John A. Boehner of Ohio, said that Republicans would “fight the president tooth and nail,” and that they were weighing whether to try to cripple Mr. Obama’s plans with legal challenges or halt them by canceling their funding.
But the White House is planning a quick start, according to officials familiar with the plans. It is breaking eligible immigrants into staggered groups, some of which will begin applying for deportation deferrals within a few months. If that happens, Republicans will have to decide whether to shut down programs that are already bringing immigrants out from underground and giving their families relief from the constant threat of separation.
According to administration officials familiar with the plans, the president will give deportation deferrals and work permits to people in the country illegally whose children are American citizens or legal permanent residents, if the parents have lived here for at least five years. As many as 3.3 million immigrants could be eligible.
Officials are hoping that by centering the reprieve program on American citizens and legal residents, they will blunt some Republican opposition. Americans cannot be deported from their own country, and deportations of their parents have left many children stranded here, often with serious consequences for their social progress.
The White House is also considering expanding a program Mr. Obama started in 2012, called Deferred Action for Childhood Arrivals, or DACA, which has given similar reprieves to nearly 600,000 young immigrants who came here as children. More than 700,000 additional young people could become eligible. Officials may also include the parents of immigrants with DACA deferrals in the new programs.
White House officials have declined to comment about the plans. They say no final decisions have been made on the scope of the programs or whether they will be announced this week or in December.
Mr. Obama’s actions will not make it easier for migrants to cross the southwestern border, like the thousands of youths without their parents who floated on rafts across the Rio Grande into South Texas over the summer. Foreigners caught at the border would still be on the priority list for deportation, administration officials said, and a primary goal of Mr. Obama’s actions will be to shift resources and agents to border security that had been focused on removing immigrants from the interior.
Administration lawyers said they were preparing their case that enacting such measures would be within Mr. Obama’s constitutional authority. They cited the president’s wide latitude in enforcing the nation’s immigration laws.
Congress has provided only enough funding for the administration to carry out about 400,000 deportations each year. Mr. Obama, to the dismay of immigrant-rights advocates, has met that goal, removing more than two million immigrants while in office. But with 11.3 million people in the United States illegally, the lawyers’ argument goes, enforcement agents will never be able to deport them all. The president, officials say, has to devise policies that allow enforcement agents to go after convicted criminals and others who pose serious threats to public safety and national security.
“The system that Congress has created and funded relies heavily on discretion,” said Hiroshi Motomura, a law professor at the University of California, Los Angeles, who studies executive powers in immigration. “The president needs to have enforcement priorities, and he needs to apply them in a way that is uniform, predictable and nondiscriminatory.”
Until now, Mr. Obama had kept deportation numbers high as part of a strategy to win Republican support for a bill overhauling the immigration system, leading angry immigrant-rights advocates to call him “the deporter in chief.” But his approach did not win over House Republicans, and the federal authorities have struggled to rein in the pace of enforcement. Now, the president is turning around and offering wholesale relief to immigrants who officials say pose no known security or criminal threat.
Republicans argue that the deportation deferrals Mr. Obama is likely to issue were intended to be used rarely, for people with compelling needs. By offering them to millions, they say, he is blocking immigration agents from enforcing the law.
“This executive order would be a violation of the president’s oath of office and a blatant abuse of power,” said Representative Lamar Smith of Texas, an outspoken opponent of Mr. Obama’s policies. “The president has sworn an oath of office to uphold the laws, but now he is planning to rewrite them on his own.”
The White House is gambling on a surge of support from immigrants and Latinos that would make Republicans think carefully about how far to go to halt the programs. Latino groups are mobilized, pressing the president to include as many as seven million immigrants.
“The time for big, bold, unapologetic administrative relief is now,” said José Calderón, president of the Hispanic Federation, a nonprofit advocacy group.
Despite the rebuke he received in the elections, Mr. Obama has responded defiantly to Republicans warning him not to act on his own.
“My executive actions not only do not prevent them from passing a law that supersedes those actions,” he said at a news conference on Nov. 5, “but they should be a spur for them to actually try to get something done.”
A version of this news analysis appears in print on November 16, 2014, on page A23 of the New York edition with the headline: Obama Plan Could Grant Papers To Millions, at Least for Now .