A bipartisan group of Senate negotiators announced today that they had reached broad agreement on comprehensive immigration reform, clearing the way for floor debate to begin Monday.

Supporters of the deal hailed the compromise as the best possible legislation the Senate could achieve and predicted broad bipartisan support.

Sen. Lindsey Graham (R-S.C.) said he expected support for the bill “will be overwhelming so long as the agreement holds together.”

“When our colleagues listen to the product, I believe the overwhelming view will be that this is the last best chance to pass immigration reform on our terms,” Graham said. “As a Congress, if this collapses, it will be years before it could be re-created.”

The agreement would include a variety of border and employment measures — ranging from additional fences along the Southern border with Mexico to stepped-up enforcement of prohibitions on hiring illegal immigrants — which would act as triggers for implementation of new immigration programs. Additionally, the bill has a focus on family reunification, which has been a major sticking point in the negotiations.

Homeland Security Secretary Michael Chertoff said he had gone over the agreement with President Bush and that he was pleased with the work. Bush “described this as an historic moment and looks forward to signing this bill when it makes its way through Congress,” Chertoff said.

Sen. Edward Kennedy (Mass.), the Democrats’ lead negotiator, agreed, saying the key will be to get a bill to the floor as quickly as possible to allow the Senate to work its will. The draft of the legislation is expected to be prepared later today or early tomorrow, with consideration beginning Monday.

“My own sense is that our position will be enhanced measurably,” once the bill gets before Senators, Kennedy said.

But Senate aides on both sides of the aisle warned that conservative and progressive interest groups and lawmakers had yet to fully buy into the package and their support remains uncertain.

The agreement came several hours after talks appeared to have broken down over conflicts between the parties’ two wings. Aides said Sen. John Cornyn (R-Texas) — a conservative stalwart on immigration — and Sen. Bob Menendez (D-N.J.), who has taken a much more liberal position on the issue than some Democrats, both declined to endorse the deal announced Thursday.

While there were about 10 key Senators who brokered the deal over the course of the past several weeks, two were notably absent from today’s press conference: Cornyn and Menendez.

Additionally, an early morning staff session reportedly ended badly. That prompted Members to launch a series of closed-door meetings today, which ultimately brought the deal to life.

Sen. Jon Kyl (R-Ariz.), a conservative who many view as critical to bringing the agreement to bear, said afterward that those present at the announcement were those who are 100 percent behind the deal.

“Some people don’t have quite that level of confidence,” Kyl said. “But that doesn’t mean they won’t get there.”

Kyl, the No. 3 Republican leader, added that he will do his part to encourage support from his Conference for the bill as it heads to the floor.

“I’m not going to pressure anyone,” Kyl insisted. “I’m going to say why I think it’s the right thing to do, but this is a very state-specific thing.”

In a statement, Senate Majority Leader Harry Reid (D-Nev.) offered qualified praise for the agreement.

“I applaud the hard work of the bipartisan group of Senators who have proposed a new approach to comprehensive immigration reform,” Reid said. “Their agreement can serve as a starting point for the Senate debate next week. I have serious concerns about some aspects of this proposal, including the structure of the temporary worker program and undue limitations on family immigration. We need to improve the bill as it moves through the legislative process.”

In his own statement, Senate Minority Leader Mitch McConnell (R-Ky.) said, “It’s encouraging to see a group of Senators from such a wide arc of the political spectrum reach an agreement on one of the most difficult issues facing our nation. The need to secure our borders, and to have a real security infrastructure in place is critical; it’s a requirement for my support of any legislation. I believe the agreement is far stronger than the bill the Senate produced last year. I will review the text of the bill and I hope to be able to support it when the Senate turns to this issue next week.”