WASHINGTON — Putting aside party differences, Senate Republicans and Democrats coalesced Thursday around compromise legislation that holds out the hope of citizenship to an estimated 11 million immigrants living in the United States unlawfully.

"We can no longer afford to delay reform," said Sens. John McCain and Edward M. Kennedy in a statement that capped weeks of struggle to find common ground.

President Bush said he was pleased with the developments and urged the Senate to pass legislation by week's end. The vote could come today.

But the emerging compromise drew fire from both ends of the political spectrum. Conservative Sen. John Cornyn, R-Texas, likened it to an amnesty bill that cleared Congress in 1986, while AFL-CIO President John Sweeney said it threatened to "drive millions of hard-working immigrants further into the shadows of American society, leaving them vulnerable to exploitation."

Sen. Orrin Hatch, R-Utah, said the new bill isn't much different than the McCain-Kennedy bill he voted against in the Senate Judiciary Committee.

"I don't think we've reached a compromise yet," Hatch said. "I want to be helpful, I want to be compassionate, but I am against amnesty, and some approaches, no matter how they try to disguise it, are just that. . . . Immigration reform starts at the border."

Hatch said he'd like to see approval of the DREAM Act, which he proposed to allow states to provide in-state tuition for undocumented students and to allow youths who were brought here by their parents to earn legal status through avenues such as higher education or military service.

However, Hatch said he wouldn't vote for a proposal only because it included the DREAM Act, which he calls a "children's act."

"We're a nation of laws, and the laws ought to be abided by," Hatch said. "We're also a nation of immigrants, but illegal immigration undermines the rule of law."

Still, after days of partisan, election-year rancor, an overnight breakthrough on the future of illegal immigrants propelled the Senate closer to passage of the most sweeping immigration legislation in two decades.

Sen. Bob Bennett, R-Utah, said to address national security best, a bolstered border security should be combined with a guest-worker program.

"If you can document the farm workers and chambermaids . . . then it's easier to get tough on the drug dealers and the terrorists who might be trying to come in on that basis," Bennett said.

Bennett said immigration reform needs to consider the nation's rapidly changing economy in which fewer people are interested in low-skill jobs.