President Obama Offers Legal Status to Millions of Undocumented Immigrants

— -- President Obama tonight announced the most sweeping executive action on immigration in three decades, providing relief for an estimated 4.1 million undocumented parents of U.S. citizens and about 300,000 undocumented immigrants who came to the U.S. illegally as children.

"I know some of the critics of this action call it amnesty. Well, it’s not," the president said from the Cross Hall entrance to the East Room of the White House. "Amnesty is the immigration system we have today -- millions of people who live here without paying their taxes or playing by the rules, while politicians use the issue to scare people and whip up votes at election time.

"That’s the real amnesty -- leaving this broken system the way it is," Obama said. "What I’m describing is accountability."

The action will be finalized Friday with the signing of a presidential memorandum at a rally in Las Vegas. It will fulfill, at least in part, the promise Obama first made in 2008 as a candidate to lift the threat of deportation from millions of people living in the U.S. illegally.

The move means nearly half the nation's undocumented immigrants -- roughly 5 million people -- will be eligible for temporary legal status and work permits if they meet select criteria, register with the government and pay a nearly $500 fee.

The announcement set off celebrations on Pennsylvania Avenue in front of the White House and at watch parties organized by immigrant advocacy groups all around the country. It also unleashed a flurry of protests from critics who have asserted Obama is exceeding his constitutional authority and setting a dangerous new precedent.

The White House said the president's primary focus, in light of limitations on his executive power, is on keeping families united. The biggest group that will benefit is an estimated 4 million undocumented immigrants who have been in the U.S. for at least five years and who have children that were born here as American citizens.

"Undocumented workers broke our immigration laws, and I believe that they must be held accountable," Obama said. But "let’s be honest -- tracking down, rounding up, and deporting millions of people isn't realistic. Anyone who suggests otherwise isn't being straight with you.

"That’s why we’re going to keep focusing enforcement resources on actual threats to our security. Felons, not families. Criminals, not children. Gang members, not a mother who's working hard to provide for her kids," Obama said.

The president's order will also extend legal status to a larger universe of so-called Dreamers, who first came to the U.S. illegally as children and either are attending school, have graduated high school or have served in the military. As many as 270,000 more undocumented immigrants will be able to apply for legal status under the program, which Obama first unveiled in 2012, administration officials said.

All immigrant applicants must have clean criminal records, provide their biometric information and pay a fee of around $500, officials said. The legal status will only last three years but can be renewed. The president's executive action does not create a pathway to citizenship or allow access to federal health care benefits.

The application process won't begin until the spring of 2015, according to the Department of Homeland Security.

In addition to deportation relief, Obama has also directed that immigration enforcement agencies focus on those who have committed felonies and those who have crossed the border within the last year. By forgoing crackdowns on those without criminal records and who have been here longer, the White House claimed it will be able to devote more resources to border enforcement and cracking down on those who pose a threat.

"Today is an important step toward rational and humane enforcement of immigration law," AFL-CIO president Richard Trumka said in a statement.

Republicans, Democrats Question Obama's Action

Ahead of the president's address, Republicans were sharply critical of Obama's move to circumvent Congress, some vowing to sue the administration and others warning it would spoil any attempt at bipartisan compromise over the next two years.

"Instead of working together to fix our broken immigration system, the president says he’s acting on his own. But that is just not how our democracy works," House Speaker John Boehner said in a short video statement posted on YouTube. "The president has said before that 'he’s not king' and he's 'not an emperor,' but he sure is acting like one. And he’s doing it a time when the American people want nothing more than for us to work together.”

"I know some of the critics of this action call it amnesty. Well, it’s not," Obama said tonight. "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."

But even some congressional Democrats questioned Obama's unilateral action, expressing preference for a more permanent solution through legislation.

"It is clear the immigration system in this country is broken, and only Congress has the ability to change the law to fix it," said Sen. Joe Donnelly, D-Indiana. "I am as frustrated as anyone that Congress is not doing its job, but the president shouldn't make such significant policy changes on his own."

Said Sen. Angus King, I-Maine, "I am concerned if the president's action goes too far, that, No. 1, it will set the cause back, that it will inflame our politics, get us into a kind of retribution situation with the opponents of immigration reform, and really change the subject from immigration to the president and whether he should've done what he did."

"I know the politics of this issue are tough," Obama said during his address. "But let me tell you why I have come to feel so strongly about it. Over the past few years, I have seen the determination of immigrant fathers who worked two or three jobs without taking a dime from the government, and at risk at any moment of losing it all, just to build a better life for their kids.

"I’ve seen the heartbreak and anxiety of children whose mothers might be taken away from them just because they didn’t have the right papers," the president added. "I’ve seen the courage of students who, except for the circumstances of their birth, are as American as Malia or Sasha; students who bravely come out as undocumented in hopes they could make a difference in a country they love. These people -- our neighbors, our classmates, our friends -- they did not come here in search of a free ride or an easy life. They came to work, and study, and serve in our military and, above all, contribute to America’s success."

ABC News' Erin Dooley contributed to this report.