WASHINGTON — Unemployment benefits for 1.3 million of the long-term unemployed — and millions more in the future — were imperiled on Tuesday after Senate efforts to reach accord on legislation to revive them collapsed in partisan finger-pointing.

After days of negotiations, Senator Harry Reid of Nevada, the majority leader, abruptly called a vote to end debate on two Democratic measures that would extend benefits for out-of-work Americans for at least three months, gambling that he could muster enough support from moderate Republicans to move on to final passage for at least one of the proposals.

But both votes failed, and the possibility of a bipartisan deal collapsed during procedural arguments, with Democrats and Republicans accusing one another of negotiating in bad faith.

Some senators remained optimistic that they would still be able to reach a compromise, but the earliest they are likely to return to the legislation is at the end of the month, when they return from a weeklong break.