The Senate voted 33-63, falling 27 short of the 60 votes needed in the 100-member chamber to limit debate and advance the major overhaul toward passage. The action followed a series of amendments that upset a delicately balanced compromise hammered out by a bipartisan group of senators and the White House.

The move was a serious blow to the comprehensive effort to overhaul immigration law before President George W. Bush leaves office in January 2009.

Senate Minority Leader Mitch McConnell of Kentucky said his fellow Republicans needed more time to work on the bill that ties tough border security and workplace enforcement measures to a guest-worker program and a plan to legalize an estimated 12 million illegal immigrants.

The 33 votes to shut off debate were 27 short of the 60 needed by Democratic Leader Harry Reid of Nevada to bring to a conclusion debate on legislation to grant legal status to 12 million undocumented aliens. He said he would seek another vote later today. If it fails, ``the bill's gone,'' Reid said. ``What else can I do?''

Reid appealed to Bush to twist the arms of Republicans who voted against limiting debate, saying an inability to pass the legislation would produce headlines that the ``president fails again.''

``This is the president's bill. He has worked long and hard,'' Reid said. ``This bill that's on the floor is not a Democratic bill, it is a bill that was worked on by Democrats and Republicans in cooperation with the president.''