Millions of immigrants living illegally in the United States could earn a chance at citizenship under a sweeping Senate proposal to be released Tuesday that would represent the most ambitious overhaul of the nation’s immigration system in three decades.

The highly anticipated proposal from an eight-member bipartisan group also aims to stem the flow of undocumented immigrants into the country by creating tens of thousands of new visas for foreign workers in low-skilled jobs, according to a 17-page summary of the bill obtained by The Washington Post.

In addition, billions of dollars would be invested in new border-control measures, including surveillance drones, security fencing and 3,500 additional federal agents charged with apprehending people attempting to enter illegally from Mexico.

The legislation — marking the first comprehensive effort since a 2007 plan died in the Senate — is intended to largely solve the problem of illegal immigration while clearing a backlog of millions of foreigners trying to enter the country through legal channels.

The senators declined to discuss the details of the bill, but members of the group briefed colleagues in both congressional chambers Monday night, including the Congressional Hispanic Caucus, aides said. The group had planned to unveil its proposal at a high-profile Tuesday news conference, but that event was canceled in light of the deadly bombings at the Boston Marathon, legislative aides said late Monday.

At the White House, the Obama administration reacted positively to the news that the group had a deal. President Obama, who won 71 percent of the Latino vote last fall, has made immigration reform his top second-term priority.

“The president is very pleased with the progress we’ve seen thus far,” press secretary Jay Carney said. “We will evaluate the legislation when we get the final language. But what we have seen is a remarkable, in Washington, level of consensus between and support for bipartisan and comprehensive immigration reform. . . . And we remain cautiously optimistic that this progress will lead to legislation that can pass and the president can sign.”

Two members of the group, Sens. Charles E. Schumer (D-N.Y.) and John McCain (R-Ariz.), will meet with Obama on Tuesday to discuss the bill, said a person familiar with the schedule.

The Senate Judiciary Committee has scheduled hearings Friday and Monday on the bill, which is hundreds of pages long. Opponents of a deal have denounced portions of the plan, and some senators are expected to offer a flurry of amendments designed to upset the fragile balance of the agreement. Similar tactics helped doom the 2007 effort.

“This is legislation that rivals in impact the health-care legislation,” Sen. Jeff Sessions (R-Ala.), a leading critic of the reform effort, said in an interview Monday. “It needs careful scrutiny. Having a hearing Friday and Monday when most members of the Senate aren’t even here is proof that they desire no real public airing on the issues. That’s very unacceptable.”

Each provision in the legislation was rigorously negotiated in two dozen private meetings with the senators, but it is the path to citizenship that is likely to cause the most vigorous public debate.

Many Republicans oppose such a plan, saying it rewards lawbreakers by granting them amnesty. But advocates say most undocumented immigrants live in fear of deportation despite being otherwise lawful residents who came seeking employment or to be reunited with their families.

The Senate bill would allow most undocumented immigrants who arrived in the country before Dec. 31, 2011, to immediately gain “registered provisional” status after paying a $500 fine and back taxes, provided they have not committed a felony or three misdemeanors.

They could then apply for permanent resident status in 10 years after paying additional fees. Three years later, they could apply for citizenship, according to the plan summary. The fastest path to full citizenship would take 13 years, according to the legislation, but it could take longer in some cases, Senate staffers said.

The path would be easier for “Dreamers” — people brought to the country illegally by their parents at a young age — who would be able to apply for a green card in five years and citizenship immediately thereafter. Foreign farmworkers would have a similar path to help patch a shortage of such workers in the country.

“We’re in the fifth year of very high unemployment,” said Roy Beck, chief executive of Numbers­USA, a group that advocates for lower immigration. “We’re in a terrible situation for American workers. People at the lower levels have seen real wages decline. Given that backdrop, why would you grant people amnesty?”

The senators say the bill will require the government to implement strict new border-control measures — including up to $7 billion in new surveillance drones, fencing, border guards and workplace tracking systems — before the undocumented immigrants are granted green cards. The bill stipulates that the government must surveil 100 percent of the border and apprehend 90 percent of the people trying to enter illegally in high-risk sectors.

“Amnesty is the forgiveness of something. In fact, there will be consequences for having violated the law, the type of consequences that ensure that there’s no incentive to do it this way again,” Sen. Marco Rubio (R-Fla.), a member of the bipartisan group, said on NBC’s “Meet the Press” on Sunday.

Obama has said he will not support a path to citizenship that is tied to specific “triggers” on border control. Asked whether the president could accept the border-control principles in the Senate group’s proposal, Carney responded: “I think that while we have not seen final language on the legislation that the Gang of Eight will be putting forward, as we understand it, it is consistent with the president’s position.”

While trying to address the problem of illegal immigration, the Senate bill also aims to clear a backlog of more than 4 million foreigners around the world who have applied for family-based visas to be reunited with relatives in the United States.

But the proposal would also put more emphasis on “merit-based” work skills than on family ties over the ensuing years.

The bill proposes eliminating 70,000 green cards reserved for brothers, sisters and adult married children of U.S. residents, as well as a diversity lottery aimed at giving green cards to people selected at random from foreign countries each year.

On the flip side, the legislation would create an estimated 220,000 new green cards for people with exceptional work skills, including entertainers, scientists and professors.

Under current law, only about 14 percent of green cards are granted to people based on employment needs, but one Senate aide estimated that the percentage could eventually increase to 45 or 50 percent under the proposal.

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