WASHINGTON — Using his executive powers to go where Congress would not, President Barack Obama delivered on a promise Friday and ordered his administration to stop deporting illegal immigrants who came to the U.S. as children, a shift that could affect more than 1 million people.

The new policy allows younger immigrants to apply for a two-year renewable reprieve on deportation, providing they have no criminal record. It is unlikely to settle the nation’s bitter debate over immigration, but may be pivotal in the battle for Latino voters in the presidential campaign.

Appearing in the Rose Garden, Obama said his executive order did not provide amnesty, immunity or a path to citizenship. But he said a “temporary, stop-gap measure” was necessary because Congress had failed to pass a comprehensive immigration overhaul, as he had sought.

“These are young people who study in our schools; they play in our neighborhoods; they’re friends with our kids; they pledge allegiance to our flag,” Obama said. “They are Americans in their hearts, in their minds, in every single way but one: on paper.

“They were brought to this country by their parents — sometimes even as infants — and often have no idea that they’re undocumented until they apply for a job or a driver’s license, or a college scholarship,” he added.

Critics denounced the move as an end run around Congress that will reward illegal immigrants when many Americans are struggling to find jobs. But with both political parties desperately seeking Latino votes, the presumptive GOP nominee, Mitt Romney, was notably muted in his response, saying Obama’s order “makes reaching a long-term solution more difficult.”

The immediate aftermath was more emotional, however, for many families. Immigrant advocacy groups and supporters held boisterous rallies in Los Angeles, Houston and New York and in front of the White House to hail the suspension of a law that has wrenched families apart.

At the University of California, Los Angeles Labor Center, many held up cell phones and cameras to snap photos of the TV screen as Obama promised to “lift the shadow of deportation.”

An elated Carlos Amador, 27, coordinator of the Dream Resource Center for undocumented immigrant students, got choked up trying to express his feelings. “It’s just been hard to put words together,” said Amador, whose family came illegally from Mexico City in 1999.

Others cautioned that unlike an act of Congress, the executive order could be reversed by a future president. Young illegal immigrants have been openly challenging the White House, and they urged followers to keep up the pressure.

“This is a huge victory but it’s only the first step,” said Cyndi Bendezu, who arrived illegally in the city of South Gate, Calif., from Peru at age 4, and now is pursuing a master’s degree in higher education at Columbia University. “We’ll keep fighting.”

And some immigration lawyers were skeptical, saying illegal immigrants seeking reprieves could be targeted for deportation if their applications were denied, or ultimately reversed.

“They’re exposing themselves to the possibility of removal proceedings and the possibility that their request will be denied,” said Matthew Kolken, an immigration attorney in Buffalo, N.Y. “So it’s a tough call.”

Administration officials acknowledged the concerns, saying people could make their own decisions whether to come forward. In a conference call with reporters, Janet Napolitano, secretary of Homeland Security, described the policy as an “exercise of discretion.”

Crystal Williams, executive director of the American Immigration Lawyers Association, said many lawyers would still advise their clients to apply if they qualified. “It will give them some protection from the overriding fear that they live with, of being deported,” she said.

Under Obama’s order, illegal immigrants under 30 can stay and work, at least temporarily, if authorities decide they don’t pose a risk to national security or public safety.

They must have come to the United States before they turned 16 and stayed continuously for at least the past five years. They must also be enrolled in school, have a high school diploma or equivalent degree or be in the U.S. military. Honorably discharged veterans are also eligible.

Applicants convicted of a felony, a significant misdemeanor or multiple misdemeanors are not eligible.

As a candidate, Obama promised comprehensive immigration reform, and he faced pressure from immigrant groups that he is now courting for re-election.

His order Friday follows several largely unsuccessful attempts to slow deportations of illegal immigrants who don’t pose a threat. In the last three years, his administration has deported more than 1.1 million people, a record. About half the total were convicted of felony or misdemeanor charges, including repeat violators of immigration law, and were considered priorities for deportation.

Last June, John Morton, director of Immigration and Customs Enforcement, announced that ICE would chiefly focus on deporting dangerous criminals, not illegal immigrants with strong family ties in America and no police records, among other factors.

He issued guidelines giving prosecutors discretion to favor illegal immigrants who are close relatives of U.S. citizens, who were brought to this country as children or who have served in the U.S. military.

But the new prosecutorial discretion, and a separate review of more than 280,000 deportation cases in immigration courts since November, led to temporary reprieves for only about 6,000 people. Most were not given work permits or permanent legal status, and the total was significantly less than immigration advocacy groups had hoped.

Obama’s announcement immediately moved immigration policy back to the forefront of the presidential campaign.

During the spring primaries, strong stands on illegal immigration proved widely popular with Republicans. Romney staked out some of the toughest positions, criticizing rivals who called for creating legal paths to citizenship.

But GOP strategists worry the hard-line stance may permanently alienate the nation’s fast-growing Latino population, especially in crucial electoral states like Florida, New Mexico and Colorado. In a tight election, turnout could also make a difference in states with fewer Latinos, such as Iowa and Virginia.

Romney agreed with Sen. Marco Rubio, R-Fla., a Cuban American who says he has been drafting legislation for young illegal immigrants, and who called Obama’s action “a short-term answer to a long-term problem.”

“I believe the status of young people who come here through no fault of their own is an important matter to be considered and should be solved on a long-term basis so they know what their future would be in this country,” Romney told reporters.

For Obama, the move could help solve one of the biggest worries hanging over his re-election efforts — flagging enthusiasm among Latino voters. Some Democrats worry that these voters, discouraged by the recession, may simply stay home. Gallup surveys from this spring showed only about two-thirds of Latino voters said they definitely planned to vote in November, compared to about 80 percent of non-Latino whites.

The path to Obama’s surprise announcement began about two months ago, according to White House aides and members of Congress.

On April 25, several senior Democratic senators — including Richard J. Durbin of Illinois, sponsor of the DREAM Act that failed in Congress — met with White House public policy director Cecilia Munoz and other West Wing aides, according to a source familiar with the talks. The senators argued that Obama should use his executive powers to simply order a halt in deportations of young illegal immigrants.

Over the next several weeks, White House lawyers studied the president’s authority over immigration enforcement actions, and finally gave their support.

The news cheered Alaa Mukahhal, 25, of Chicago, who came to the U.S. from Kuwait with her parents in 1993, when she was 6. Despite earning an architecture degree from the University of Illinois, Mukahhal is facing deportation proceedings that started after she applied for asylum.

“We understand this is a temporary move, but it’s an important step forward,” she said. “As far as I’m concerned, growing up on the South Side of Chicago, I’m as American as they come.”