‘‘This amendment will put to rest any remaining credible concerns about the border, about border security,’’ Senate Majority Leader Harry Reid, D-Nev., said on the Senate floor as he filed the measure and announced procedural steps to bring it to a vote early next week. ‘‘The opposition of a small group is not going to stop this bill from moving forward,’’ Reid said.

With the border security amendment finalized, the immigration legislation immediately picked up an additional likely Republican supporter: Sen. Lisa Murkowski of Alaska, who signed on as a co-sponsor of the amendment.

WASHINGTON — An agreement to vastly increase fencing, patrols and high-tech monitoring along the U.S.-Mexico border was formally unveiled in the Senate Friday, providing powerful momentum to a far-reaching immigration bill backed by the White House.


The deal doubling Border Patrol agents and adding hundreds of miles of fencing along the Southwest border had already won support from four other undecided Republican senators who are now likely to back the immigration bill when it comes to a final vote next week. The legislation opening the door to citizenship for millions now appears within reach of securing the broad bipartisan majority that its authors say is needed to ensure serious consideration by the GOP-controlled House.

However, the outcome there remains far from certain because many conservatives are opposed to offering citizenship to people who came to this country illegally.

‘‘We really have tried to secure the border in a way that we hope can get bipartisan support and that Americans want,’’ Sen. John Hoeven, R-N.D., an author of the amendment, told The Associated Press in a phone interview Friday. ‘‘We’re hopeful to have a good bipartisan majority.’’

Sen. John McCain, R-Ariz., said on Fox News Channel Friday that ‘‘if there’s anyone who still will argue that the border is not secure after this, then border security is not their reason for opposing a path to citizenship for the people who are in this country illegally.’’


‘‘Is it more than I would have recommended? Honestly, yes,’’ McCain said. ‘‘But we've got to give people confidence.’’

Hoeven developed the amendment along with Republican Sen. Bob Corker of Tennessee, in consultation with McCain, Sens. Lindsey Graham, R-S.C., Chuck Schumer, D-N.Y., and other members of the so-called Gang of Eight senators who wrote the immigration bill. It prevents immigrants now here illegally from attaining permanent resident status until a series of steps have been taken to secure the border.

These include doubling the Border Patrol with 20,000 new agents, 18 new unmanned surveillance drones, 350 miles of new pedestrian fencing to add to 350 miles already in place and an array of fixed and mobile devices to maintain vigilance, including high-tech tools such as infrared ground sensors and airborne radar.

The new provisions would be put in place over a decade, in line with the 10-year path to a permanent resident green card that the bill sets out for immigrants here illegally. During that time, the immigrants could live and work legally in a provisional status.

Hoeven said the 10-year cost of the border security amendment included $25 billion for the additional Border Patrol agents, $3 billion for fencing and $3.2 billion for other measures.

It’s ‘‘border security on steroids,’’ said Corker, who along with Hoeven had been uncommitted on the immigration bill. Both are now prepared to support it, assuming their amendment is adopted. Sens. Dean Heller, R-Nev., and Mark Kirk, R-Ill., also announced their support for the deal Thursday.


White House press secretary Jay Carney said the border deal ‘‘would constitute a breakthrough’’ on immigration. ‘‘We’re pleased that Republicans and Democrats continue to work together toward comprehensive immigration reform,’’ he said.

The deal on border security came together quickly over the past several days after talks had bogged down over Republicans’ insistence that green cards be made conditional on catching or turning back 90 percent of would-be border crossers. Schumer, other Democrats and Obama himself rejected this trigger, which they feared could delay the path to citizenship for years. Obama made his objections known in a phone call to Schumer from Air Force One during his trip to Europe for the Group of Eight summit earlier in the week, according to a Senate aide who spoke on condition of anonymity to discuss private deliberations.

The breakthrough came when the Congressional Budget Office released a report Tuesday finding that the bill would cut billions of dollars from the deficit. Schumer’s top immigration aide, Leon Fresco, had the idea of devoting some of those billions to a dramatic border buildup.

Graham, who helped run interference between Corker and Hoeven and Democrats in the group, said that with the budget office finding in hand, he sat down with Schumer and Corker and said, ‘‘OK, let’s go big.’’

The idea immediately appealed to the left and the right.


For Republicans, it provided concrete assurances that the bill would aim to achieve a secure border. For Democrats, it offered goals that, if dramatic, were achievable and measurable.

Still, not everyone was won over.

Shortly before Corker and Hoeven went to the Senate floor to announce their agreement Thursday afternoon, five leading Republican opponents of the bill held a news conference to denounce the deal as little more than an empty promise.

‘‘In short, I think this amendment is designed to pass the bill but not to fix the bill,’’ Sen. David Vitter, R-La., said.

About 10 Republicans have indicated they will vote for the bill, far more than enough to ensure it will have the 60 votes required to overcome any attempted filibuster by last-ditch opponents. Democrats control 54 seats, and party aides have said they do not expect any defections.

In addition to the border security components and eventual citizenship for the estimated 11 million people living here illegally, the immigration bill would create new work visa programs and expand existing ones to allow tens of thousands of workers into the country to work in high- and low-skilled jobs.