WASHINGTON — President Obama chose confrontation over conciliation on Thursday as he asserted the powers of the Oval Office to reshape the nation’s immigration system and all but dared members of next year’s Republican-controlled Congress to reverse his actions on behalf of millions of immigrants.
In a 15-minute address from the East Room of the White House that sought to appeal to a nation’s compassion, Mr. Obama told Americans that deporting millions is “not who we are” and cited Scripture, saying, “We shall not oppress a stranger for we know the heart of a stranger — we were strangers once, too.”
The prime-time speech reflected Mr. Obama’s years of frustration with congressional gridlock and his desire to frame the last years of his presidency with far-reaching executive actions. His directive will shield up to five million people from deportation and allow many to work legally, although it offers no path to citizenship.
“The actions I’m taking are not only lawful, they’re the kinds of actions taken by every single Republican president and every Democratic president for the past half-century,” Mr. Obama said. “To those members of Congress who question my authority to make our immigration system work better, or question the wisdom of me acting where Congress has failed, I have one answer: Pass a bill.”
In a series of rhetorical questions, he cast the immigration debate in emotional terms. “Are we a nation that tolerates the hypocrisy of a system where workers who pick our fruit and make our beds never have a chance to get right with the law?” he asked. Later he added, “Whether our forebears were strangers who crossed the Atlantic, or the Pacific, or the Rio Grande, we are here only because this country welcomed them in.”
Mr. Obama intends to underscore the schism between the parties on the issue of immigration during a campaign-like rally on Friday at a high school in Las Vegas, where Hispanics are a powerful and growing voting bloc.
The trip is part of a White House strategy to try to convince Americans in the next months that Mr. Obama’s actions are legal and right. Immigration advocates plan to use that time to push for greater protections while Republicans are devising ways to defy the president and exercise their new authority.
Conservative lawmakers accused the president of abusing his office — Representative Kevin McCarthy of California, the House majority leader, called it a “brazen power grab” — and promised a fight when the Republicans take full control of Congress next year. But even before Mr. Obama’s speech, Republicans were divided about how to stop him and unsure how to express their anger without damaging their standing with Latinos.
Mr. Obama’s actions will sharpen the focus of government enforcement on criminals and foreigners who pose security threats. High-tech workers will have an easier time coming to the United States, and security on the border will be increased.
The centerpiece of the president’s announcement is a new program for unauthorized immigrants who are the parents of United States citizens. About four million people will be eligible for a new legal status that would defer their deportations and allow them to work legally. They must pass background checks and pay taxes, but they will receive Social Security cards, officials said.
To those people, Mr. Obama said, “You can come out of the shadows.”
An additional one million people will have some protection from deportation through other parts of the president’s plan.
Mr. Obama’s actions will end a program called Secure Communities, which advocates had long criticized as a dragnet that swept up many unauthorized immigrants arrested on minor offenses like traffic violations. Local police will no longer be asked routinely to detain immigrants without papers.
How Republicans choose to proceed in their opposition to the president’s directive will shape the final two years of Mr. Obama’s tenure and could help set the tone of the 2016 presidential campaign. Several Republicans on Thursday said they wanted to use a coming spending bill and the threat of a government shutdown as leverage against Mr. Obama, while others in the party reached for ways that Congress might undercut the president’s actions by withholding money or threatening other priorities.
“By ignoring the will of the American people, President Obama has cemented his legacy of lawlessness and squandered what little credibility he had left,” House Speaker John A. Boehner said in a statement after the speech.
Even as Republican lawyers analyzed what the White House said was the legal basis of Mr. Obama’s actions, it remained unclear how they might undo them. The agency that will carry out most of the president’s executive actions, Citizenship and Immigration Services, is funded with application fees, and does not rely on a budget vote in Congress to keep operating.
But accusations of a presidential abuse of power appear to have gained traction in recent days, as a Wall Street Journal/NBC News poll found just 38 percent support for Mr. Obama’s executive actions even as there was broad support for a path to citizenship for unauthorized immigrants. In the poll, 48 percent said they opposed Mr. Obama’s actions. Even a few Democrats have expressed concern about the propriety of the president’s actions.
“The president shouldn’t make such significant policy changes on his own,” Senator Joe Donnelly, Democrat of Indiana, said in a statement before the president’s speech. Senator Joe Manchin III, Democrat of West Virginia, told White House aides in a meeting on Thursday that he disagreed with Mr. Obama’s action.
“To put it through now is the wrong thing to do,” Mr. Manchin said after the meeting. “I told them I wasn’t comfortable.”
But Mr. Obama insisted that his actions were consistent with powers that have been exercised by presidents in both parties for decades.
Immigration advocates and the president’s Democratic allies hailed the announcement even as they insisted that more should be done to provide legal protections for millions of unauthorized immigrants unaffected by Mr. Obama’s directives.
“Five million people will get to feel this country’s embrace,” said Lorella Praeli, the director of advocacy for United We Dream, a youth immigrant organization. “But I’m sad there are people who will be left out. For them in particular, I recommit to fight until we see the day that they are protected from deportation.”
Deepak Bhargava, the executive director of the Center for Community Change, called the changes “a massive breakthrough for the immigrant-rights movement.”
Fierce critics of the president’s actions described them in equally sweeping terms.
“This is a constitutional republic, not a banana republic,” said Jenny Beth Martin, the president of the Tea Party Patriots. “It’s time we all started acting like it.”