The proposed agreement would allow illegal immigrants to come forward and obtain a "Z visa" and - after paying fees and a $5,000 fine - ultimately get on track for permanent residency, which could take between eight and 13 years. Heads of households would have to return to their home countries first.

They could come forward right away to claim a probationary card that would let them live and work legally in the US, but could not begin the path to permanent residency or citizenship until border security improvements and the high-tech worker identification program were completed.

A new crop of low-skilled guest workers would have to return home after stints of two years. They could renew their visas twice, but would be required to leave for a year in between each time. If they wanted to stay in the US permanently, they would have to apply under the point system for a limited pool of green cards.

The program drew fire from liberal groups that said it was unworkable. They had joined Democrats in pressing instead for guest workers to be permitted to stay and work indefinitely in the US, and ultimately earn the chance to stay.

"Without a clear path to permanent residence for a healthy share of the future temporary workers, we run the risk of reproducing the widespread illegality that this bill is designed to address," said Frank Sharry, the executive director of the National Immigration Forum.

Sen. Byron Dorgan , D-N.D., said he would try to kill the temporary worker program because it would bring in a potentially unlimited stream of immigrants to compete with Americans for jobs and depress wages.

In perhaps the most hotly debated change, the proposed plan would shift from an immigration system primarily weighted toward family ties toward one with preferences for people with advanced degrees and sophisticated skills. Republicans have long sought such revisions, which they say are needed to end "chain migration" that harms the economy.

Family connections alone would no longer be enough to qualify for a green card - except for spouses and minor children of US citizens. Strict new limits would apply to US citizens seeking to bring foreign-born parents into the country.

Sen. John McCain , R-Ariz., who led the charge last year to push through an immigration overhaul, called the deal "the first step" and urged moving it forward before the politics of 2008 made such action impossible.

"We all know that this issue can be caught up in extracurricular politics unless we move forward as quickly as possible," said McCain, who is seeking the GOP nomination for president.

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