The blocking of the bill also suggested a miscalculation on the part of Mr. Reid, who had tentatively scheduled a vote for 8:15 p.m. only to appear on the Senate floor at 8:40 to announce that the measure was stalled.

"I know that everyone is anxiously awaiting the 8:15 time to arrive," Mr. Reid said, joking, but there were only scattered smiles among senators in the chamber.

"It appears at this time that we are going to have to continue work on this bill," Mr. Reid said, adding that Republicans were insisting on offering additional amendments to the measure.

"We would probably be a vote short," he added.

Thinking they would need every last vote, the Democrats even brought in Senator Edward M. Kennedy of Massachusetts, who has brain cancer.

The Republican leader, Senator Mitch McConnell of Kentucky, highlighted the point that Democrats had come up embarrassingly short, saying, "Let me just underscore what the majority leader has indicated: the votes would not be there tonight."