WASHINGTON – Senate Republican and Democratic leaders yesterday declared a major breakthrough on the immigration reform debate with a new bill they said had won enough Republican Senate support by limiting the number of illegal immigrants who have a path to citizenship without leaving America, a touchpoint in Washington, where the shadow of a 1986 amnesty failure has loomed large.

Senators said President Bush provided assurance he would back the legislation, which would offer legal status to more than half of the estimated 12 million illegal immigrants in America and offer millions more temporary work visas.

As of late last night, passage of the sensitive bill was far from certain. Any legalization program faces serious challenges, beginning with strong strains of dissent in the Senate and time constraints caused by an impending Easter recess deadline. An even greater hurdle will occur in conference with the House, which passed an enforcement only bill last year, and where representatives have vowed to block any legalization program.

Yesterday, however, with election year politics on full display, both Republicans and Democrats tried to claim a victory with the compromise. Senator McCain, a Republican of Arizona who has been a chief architect of the immigration reform plan, said it was a “workable solution” that was not perfect, but “compared with the status quo is nirvana.” Senator Frist, a Republican of Tennessee and the majority leader, called it a “huge breakthrough, which will allow us to pivot in the next few hours.” Both senators have presidential aspirations.

Another key proponent of the bill, Senator Kennedy, a Democrat of Massachusetts, stressed the service to millions of illegal immigrants and their families across America. “We’re sending a message that you’re going to be welcome and you don’t have to live in fear in the future,” he said.

Others, however, charged that it was no victory. On the Republican side there were accusations again of creating an amnesty that would be a repeat of 1986, sending a message that lawbreakers are rewarded, which would result in a deluge of illegal immigrants. “It ignores the principle of circular migration, which has served our country well,” Senator Cornyn, a Republican of Texas, said. Senator Kyl, a Republican of Arizona, called the changes “artificial, meaningless, and hardly a significant change to what we had before.” And Senator Hutchinson called it a “security threat to our nation.”

From a group of Democrats concerns flared about temporary workers creating a two-tier labor system and driving down wages for Americans. John Sweeney, president of the AFL-CIO, which has been campaigning against a temporary visa program, told the Associated Press the new plan threatened to “drive millions of hardworking immigrants further into the shadows of American society, leaving them vulnerable to exploitation.”

The Senate compromise was announced after the failure yesterday morning of a test vote on proposed immigration legislation that cleared the Judiciary Committee. Democrats, concerned Republicans were introducing amendments that would stall passage or change the nature of the bill, pushed for a showdown bill.

In an effort to salvage the prospect of immigration reform, Senators Martinez of Florida and Hagel of Nebraska, both Republicans, drafted the alternative which Senator Frist introduced on the Senate floor late Wednesday night. The new plan limits a path to citizenship without leaving America to the estimated 6.7 million immigrants who arrived more than five years ago. Called by the plans backers an “earned legalization,” they say that unlike an amnesty immigrants would have to fulfill certain requirements, such as completing six years of temporary residency and paying a $2,000 fine, before they would be eligible for permanent legal status.

What the Hagel-Martinez plan changed affects primarily the 2.8 million who arrived two to five years ago. They would only have the opportunity to become legitimate by joining a new temporary worker pool by “touching base” within three years at one of America’s ports of entry. While there would be unlimited temporary visas for them to reenter, upon arriving they would have to get to the back of the line for green cards.

However, the number of employment-based green cards, currently limited to 140,000 a year, would be increased to ensure they have an opportunity to apply for permanent residency without waiting endlessly.

Additionally, measures are included in the legislation that are supposed within six years to eliminate processing backlogs, which in New York are the longest in the country and currently more than two years for green card applications. Congressional aides working on the bill predict that the process to citizenship could last as long as 13 years.

Those who arrived fewer than two years ago would not be eligible for any legalization plan unless they qualify for a special program for agricultural workers. They could, however, return to their home country and join the flow of new temporary workers.

This “guest worker” program has caused a tug of war in the last days of negotiations. Democrats, eager to placate their organized labor base, have been trying to ensure the number of guest workers is set low. Republicans, pushed by business interests, have worked to increase it. Senators Obama, a Democrat of Illinois, and Feinstein, a Democrat of California, came out with an amendment to reduce the number of guest workers.

Optimistic that this and other kinks could be worked out, Senator McCain stressed the real challenge would be when the legislation reached the House. Looking ahead to that looming problem, Senator McCain said a letter was being drafted yesterday saying, “Republicans will vote against a conference report that would destroy this very delicately-crafted compromise.”