Greece’s limping economy yields large trade and budget deficits, and none but the European Central Bank, the European Commission and the International Monetary Fund — known collectively as the troika — are willing to lend the nation the money it needs to stay afloat. The troika is demanding more concessions to placate Germany and other northern European countries, where the bailout of Greece is a hard sell to voters. For its part, Greece is trying to preserve social and political cohesion in the face of growing unrest, political extremism and a devastated economy that is expected to worsen with more austerity. And the feeling is growing here and abroad that the troika’s strategy for Greece is failing.

The leaders of two of the three major political parties in Prime Minister Lucas Papademos’s interim coalition government — the Socialists and the center-right New Democracy party — agreed on the new round of austerity after days of tense debate, maneuvering and threats. The leader of the third, the right-wing Popular Orthodox Rally, refused to endorse the measures and later withdrew from the coalition.

In the debate on Sunday night before the vote, Mr. Papademos appealed to lawmakers to do their “patriotic duty” and pass the measures, saying they would be saving Greece from bankruptcy in March, when a bond issue comes due that Greece cannot repay without foreign help.

In a sign of how the crisis has frayed the political order in Greece, the three leading political parties all moved swiftly to expel lawmakers who had broken ranks with leaders in the voting.