WASHINGTON &

Key senators and the White House are eager to push their bipartisan immigration deal through the Senate by Memorial Day, but as details of the bargain emerged today, hope for that deadline was slipping.




Critics of the measure denounced its key elements, including its quick grant of legal status to millions of unlawful immigrants, and said they would seek to revise it.




Sen. Jeff Sessions, R-Ala., said it was "unthinkable" that the Senate would complete the measure this week, issuing a thinly veiled filibuster threat should proponents try to speed it through.




"I'm prepared to use whatever tactics are appropriate to resist that," Sessions told reporters.




Tensions run high on immigration, and the bargain reached last week sparked intramural hostility between Sen. John McCain, R-Ariz. and Sen. John Cornyn, R-Texas, who had a bitter exchange during the last closed-door meeting before a deal was announced.




Cornyn, who opposes the agreement, said that McCain, a supporter, has apologized to him for launching a profanity-laced tirade at the Texan accusing him of holding up the deal.




"I don't think anything was said that people in that room hadn't heard at some other time before in their lives, but it was pretty clear that (McCain) wanted us to move forward so they could announce their agreement," Cornyn said.




Sen. Kay Bailey Hutchison, R-Texas, said she has "great concerns about the bill," and announced she would seek to alter it to mandate that illegal immigrants go back to their home countries before gaining legal status.




Under the proposal, that requirement only applies to heads of households seeking green cards and a path to citizenship. The estimated 12 million immigrants here unlawfully could obtain visas to live and work in the U.S. indefinitely without returning home.




"I do have concerns that people can come here and not ever have to go back and get right with the system," Hutchison said. She and Cornyn spoke on Fox News.




Sessions planned to spend the afternoon laying out his worries about the legislation &

which was distributed to senators over the weekend &

in a Senate floor speech.




Sen. Mitch McConnell of Kentucky, the Republican leader, has warned that the immigration debate is likely to tie up the Senate for a while.




"It's got to go on for at least a couple of weeks to give everybody the opportunity in the Senate to feel like they've had their chance to offer amendments that they think would improve the bill," McConnell said.




The bill, scheduled for Senate debate today, would toughen border security and create strict workplace enforcement rules to prevent illegal immigrants from getting jobs. It would also institute a new point system to prioritize employability over family ties in deciding who can immigrate to the U.S. in the future.




Massachusetts Sen. Edward Kennedy, the lead Democratic negotiator, said the bill would create "a tough but fair path to citizenship" for millions of immigrants.




"The bill isn't exactly the way I would have written it, but it is a strong compromise and the best chance we will have to finally fix this broken system," he said.