WASHINGTON – The sweeping immigration overhaul endorsed by President Bush was stopped cold in the Senate on Thursday night, leaving the future of one of the administration’s chief domestic priorities in serious doubt. After a day of tension and fruitless maneuvering, senators rejected a Democratic call to move toward a final vote on the compromise legislation after Republicans complained they were not given sufficient opportunity to reshape the bill. Supporters of cutting off the debate got only 45 of the 60 votes they needed; 50 senators opposed the cutoff. The outcome, which followed an outpouring of criticism of the measure from core Republican voters and from liberal Democrats as well, was a significant setback for the president. It came mainly at the hands of members of his own party after he championed the measure in the hope of claiming it as a major achievement on domestic policy in the last months of his administration. It was also a disappointment for a bipartisan group of about one dozen senators who met privately for three months to broker a compromise that tried to balance a call for stricter border enforcement with the push to find a way for many of the 12 million people who are illegally in the country to qualify for citizenship eventually. “The majority is simply not going to get anywhere trying to stuff the minority,” said Sen. Mitch McConnell of Kentucky, the Republican leader. The morning vote sent Senate leaders and backers of the legislation scrambling, trying to reach an agreement to salvage the measure with the help of administration officials. Homeland Security Secretary Michael Chertoff was also consulted by phone. As late as 6:30 p.m., Sen. Edward M. Kennedy, D-Mass., a chief architect of the legislation, was asked if he had the votes to force an end to the debate. “It’s touch and go,” Kennedy said. “It’s extremely close at this time. Republicans have held their cards.” If conservative Republicans continue objecting to the consideration of Republican amendments, Kennedy said, “we’ve really got a stalemate here.” But if the bill does not pass in the next few days, Kennedy said, the Senate will find another way to address the issue. “The issue is not going to go away,” Kennedy said. “We are not going to go away.” 160Want local news?Sign up for the Localist and stay informed Something went wrong. Please try again.subscribeCongratulations! You’re all set! Senate conservatives fought the legislation from the start, saying it rewarded those who broke the law by their illegal entry into the country. After winning a few important changes in the measure, Republican critics demanded more time and colleagues supported their calls for more opportunity to fight it out on the Senate floor. Sen. Harry Reid, D-Nev., the majority leader, said the critics of the bill were simply stalling and would never be satisfied. He attributed the failure of the bill to Republican recalcitrance. “We’ve done more than our share,” Reid said. “We’ve sent all the signals we can to get the president to help. It’s his bill.” Reid did leave the door open to returning to the bill later this year. The vote was the second attempt of the day to cut off a debate that had gone on for nearly two weeks, interrupted by the Memorial Day recess. On the initial showdown in the morning, the Senate fell 27 votes short of the 60 required; every Republican and 15 Democrats opposed the move.