The Obama administration kicked off one of the most sweeping changes in immigration policy in decades Wednesday, accepting applications from young illegal immigrants for the temporary right to live and work openly in the United States without fear of deportation.

An estimated 1.7 million young people who arrived in the United States illegally as children could qualify for the new Department of Homeland Security program, and thousands are expected to pay the $465 application fee for a “deferred action” permit that would protect them from deportation for at least two years. Many began lining up earlier this week at their native countries’ embassies and consulates to get passports and other records needed to apply.

Immigrants have waited for final details of the plan in the two months since President Obama pledged to brush aside years of congressional stalemate over the Dream Act and grant de facto residency to qualified immigrants.

On Tuesday, officials surprised advocacy groups by posting the application forms online one day early. Advocates across the country planned workshops Wednesday for hundreds of immigrants eager to learn who will qualify and how to apply.

“Starting today, this process will allow law enforcement to dedicate their efforts to going after violent criminals and those who pose risks to our national security, while preserving opportunity for thousands of young people,” Senate Majority Leader Harry M. Reid (D-Nev.) said in a statement. “This is smart policy that will enhance our nation’s security while removing the specter of deportation that haunts DREAMers.”

Saying that “the onus is on Congress to permanently fix our broken immigration system,” Reid called on Republicans to “help us pass the DREAM Act along with comprehensive immigration reform that is tough, fair and practical.”

The National Alliance of Latin American and Caribbean Communities urged eligible young people to apply for the program “with the benefit of experienced legal advice.”

“Even though DA [deferred action] is only a temporary immigration relief initiative, it represents the largest immigration benefit application process since the 1986 immigration reform law,” said alliance board member Patricia Montes.

Families have been scrambling to assemble school records, utility bills and other documents that may be needed, advocates said.

“People are very, very anxious to file, so we’ve been telling them to over-prepare,” said Emid Gonzalez, manager of legal services at Casa de Maryland. The group scheduled an afternoon workshop Wednesday at which she expects to see family documents by the armload. “The phone has been ringing off the hook.”

The program is open to immigrants ages 15 to 31 who came to the country before they were 16 and have lived here continuously for at least the past five years. Among other restrictions, they must be free of serious criminal convictions, be enrolled in or have completed high school, or have served in the U.S. military. On Tuesday, officials confirmed that those enrolled in GED programs and certain training programs will also qualify, broadening the program’s potential reach.

U.S. Citizenship and Immigration Services also provided a list of documents it will accept as proof of continuous residency, including tax receipts, bank records, and church confirmation and other religious records.

On Antonio Aleman’s dining table in a double-wide trailer in Suitland, the pile of birth certificates and school transcripts grew to nearly a foot tall Tuesday as he prepared to sign up his two children, 15 and 21. With his wife Ruth slapping fresh tortillas in the kitchen, Aleman sorted through his daughter Beatrize’s academic bona fides, including a certificate of achievement from Surrattsville High School.

“I think they will qualify. They are good students; we’ve been working hard, paying our taxes,” said Aleman, 43, a bakery truck driver from El Salvador who said his family came nine years ago and overstayed their visas. He already bought two money orders for $465 each to cover the application fees. “It’s been difficult to wait. What else do we need? Do we have everything?”

The protected status has to be renewed every two years. And the program’s name, Deferred Action for Childhood Arrivals, may lack the aspirational heft of the “Dream Act.” But immigration advocates were treating Wednesday’s launch as a great victory.

“This is single largest opportunity we’ve had since [the amnesty program of] 1986 to bring people out of the shadows and into documented status,” said Rep. Luis V. Gutierrez (D-Ill.), who led efforts to pass the Dream Act in the House only to see it fail in the Senate in 2010. “We’ve got to take advantage of it. Our goal should be to sign them up, sign them up, sign them up.”

Activists plan to hold regular events over the next several months to draw into the program eligible immigrants, many of whom will be averse to revealing their names and addresses to federal authorities.

But more than 5,000 have registered for an information session Gutierrez planned Wednesday at Chicago’s Navy Pier. Mayor Rahm Emanuel and Sen. Richard J. Durbin (D-Ill.) planned to attend, basking in an election-year initiative that Democrats hope will please Latino voters after years of record deportations.

“This is such a contrast to the years of deportation,” Gutierrez said. “The rewards are going to be huge.”

Critics said politics explains everything about a program they characterize as amnesty for lawbreakers at a time of soaring joblessness. “With unemployment at 8.3%, it’s unconscionable that the Obama administration’s amnesty program actually requires illegal immigrants to apply for work authorization in the U.S.,” said Rep. Lamar Smith (R-Tex.), chairman of the House Judiciary Committee, in a statement. “This undercuts the 23 million unemployed or underemployed Americans.”

Opponents also complain about the costs. Homeland Security officials will rule case-by-case on applicants, presenting huge personnel demands. Officials say they hope to pay for caseworkers with the application fee.

Opponents and supporters alike agree that the two-year protections are likely to be renewed indefinitely, as has been the case with Haitian refugees and others who have gotten such status. While future administrations may stop granting the protections, they are unlikely to move to deport those already enrolled.

“There’s no way Romney is going reverse this, at least not for those who already have it,” said Mark Krikorian, head of Washington’s Center for Immigration Studies, which favors tighter restrictions on immigration.

For some young immigrants on the verge of being sent out of the country, the program has amounted to a tarmac reprieve. Lawyers say numerous pending deportations have been paused as immigration officials review people’s eligibility for deferred action.

Doug Stump, an immigration lawyer in Oklahoma City, has had three sets of clients like that in recent weeks. Among them were two college-student siblings within days of boarding a plane for Guatemala, a country neither had seen they were toddlers.

“They were terrified. They’ve been in this country their whole lives,” Stump said. Officials agreed to halt the proceedings when he showed the two would likely qualify for the new protections. Afterward, Stump said, “It was a tear-fest around here.”

William Branigin contributed to this report.