"Boots on the ground, drones in the air," summed up Sen. Chuck Schumer, the New York Democrat who has been at the center of efforts to push immigration legislation through the Senate.
The plan was announced by Sens. John Hoeven of North Dakota and Bob Corker of Tennessee, Republicans who had been publicly uncommitted on the legislation. Both said other GOP fence-sitters would also swing behind the measure if the changes were incorporated, and by late in the afternoon, two had done so.
A final vote on the legislation is expected by the end of next week.
The next move would be up to the House, where majority Republicans are overwhelmingly opposed to granting citizenship to immigrants living in the United States illegally. Talks on any final compromise would be held in the fall if then.
The White House declined to respond to requests for comment on the Senate proposal, even though congressional officials said administration officials were involved in the formal drafting of the terms. Obama met at the White House recently with key Democrats to discuss the measure, and kept apprised of the negotiations while on his just-completed European trip.
Under the emerging deal, an estimated 11 million immigrants living in the United States illegally would be eligible to obtain legal status while border security was increased. They could not be awarded green cards, which bestow permanent residency status, until the entire border enhancement plan had been put into place.
That effectively would give the government a decade to set up the additional security, since the legislation envisions a pathway to citizenship that gives immigrants provisional status after six months but requires them to wait at least a decade before they become eligible for green cards.
Despite the changes, the legislation appeared certain to retain the basic contours negotiated over many months by a so-called Gang of Eight, four senators from each party.
Whatever its impact on the bill's prospects, the deal failed to satisfy a group of conservative Senate critics who want proof that the border has been secured before legalization begins, rather than the mere placement of new agents and equipment.
"My impression is this is a promise of future performance and there is no contingency in the form of a trigger" to assure its effectiveness, said John Cornyn, R-Texas.
Sen. Jeff Sessions, R-Ala., also cautioned that the highly touted agreement had not been drafted yet, much less read by members of the Senate and their staffs.
The legislation has a broad array of outside interests pushing for its passage, although two organizations objected to the plan for changes.
Speaking for CAMBIO, an organization that favors immigrant rights, Christian Ramirez said the deal should include lapel cameras to deter abuse by border agents, as well as the placement of 1,000 distress beacons in the desert.
The ACLU called the proposed agreement a "massive deployment of force" that would be "simply devastating for border communities."
Corker and Hoeven both said they expected the legislation to be formally unveiled in the Senate late Thursday.
The agreement was a turn in the Senate spotlight for the two men, who have spent days in secretive talks with fellow Republicans, and then with Schumer and Democratic Sen. Bob Menendez of New Jersey.
"We must secure the border first" before anyone in the country illegally can gain citizenship, Hoeven said on the Senate floor. "That's what Americans demand and that's what we must do." He said the 10-year cost included $25 billion for the additional Border Patrol agents, $3 billion for fencing and another $3.2 billion for other measures. Other officials said the overall cost of the security upgrade could reach $40 billion over a decade.
Corker told reporters the plan amounted to 'border security on steroids" and said it would impart "tremendous momentum" to the bill on the Senate floor. By day's end, Republican Sens. Mark Kirk of Illinois and Dean Heller of Nevada said they, too, were prepared to vote for the bill if the changes were incorporated.
That brought to 10 the number of Republicans who have indicated they will vote for the bill, far more than enough to assure it will have the 60 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 from their side of the political aisle.
Apart from the border security measures, the legislation as drafted already included implementation of a biometric system to track the comings and goings of foreigners at air and sea ports as well as land crossings, and a requirement for businesses to verify the legal status of job seekers.
At the same time the border security talks appeared all but settled, officials disclosed changes on other thorny issues.
Under one of them, sought by Sen. Orrin Hatch, R-Utah, immigrants would not be able to claim credit for Social Security taxes they paid while working without lawful status. Credits are used to determine the amount in benefits a worker receives from the program after retirement.
Also under discussion was a second proposal by Hatch to prohibit the federal government or the states from making immigrants eligible for welfare until they had held legal status for five years.
Officials also said the White House had taken a role in drafting a change to clarify when immigrants would become eligible for federal subsidies under the health care law that is now taking full effect. Details were not immediately available.
Democrats and Republicans alike said Sen. Rob Portman, R-Ohio, was pressing for a toughening of the E-Verify program, and that a small group of Southern Republicans wanted changes made to a new program that would permit farm workers from other countries to work in the United States temporarily. The outcomes of those talks and the votes of several Republicans as well were unclear.
In addition to border security issues, the legislation would increase the number of visas going to high-skilled workers whose labor is sought by U.S. technology firms, create a new program for lower-skilled immigrants and allow farm laborers to come to the country temporarily to perform seasonal jobs.
Separately, younger immigrants who came to the United States illegally as children would be eligible for legal status more quickly than others.
For foreigners looking to move to the United States legally, a decades-old system that emphasizes family ties would be replaced by one that gives more weight to education, work skills, English proficiency and relative youth.