“What has happened in Greece in the last few years is a stain on European civilization,” said Mr. Tsipras, who looks set to become Greece’s next prime minister, or at least its kingmaker in Parliament, if his party’s popularity holds.

Anger at Germany, whose chancellor, Angela Merkel, has resisted any write-off of Greek debts, is widespread across much of Southern Europe but is particularly acute in Athens. Unidentified gunmen in late December opened fire with an assault rifle on the residence of the German ambassador. Nobody was hurt.

On the day Mr. Tsipras skipped a ceremony attended by José Manuel Barroso, the president of the European Commission, and by other dignitaries from Brussels, Mr. Samaras’s party, New Democracy, denounced Syriza as having “well-known links to terrorism.”

The accusation followed the “escape” of Christodoulos Xiros, a terrorist serving six life sentences for his role in multiple killings and bombings by the leftist guerrilla group November 17, which has been dismantled. He disappeared last Monday during a prison furlough, stirring dismay in Washington and speculation in the Greek news media of a resurgence of political violence.

New Democracy presented no evidence of any links to terrorism by Syriza, which dismissed the claim as part of a government campaign to stir public fear against the left at a time when the main threat of political violence comes from Golden Dawn, an extreme rightist party with 18 seats in Parliament. Half of these lawmakers face criminal charges for joining and organizing what prosecutors say is a criminal organization. Golden Dawn nonetheless remains Greece’s third most popular party.

“Our main enemy, our main opponent, is the fear that the government and media try to create about Syriza and a leftist government in Greece,” Mr. Tsipras said. “We are fighting for a very big change, a radical political change. In front of every change there are a lot of people who are afraid for the future.”

European and Greek leaders stressed the importance of sticking with the current course, focusing on glimmers of economic hope, particularly a possible return to growth and a sharp narrowing of a once gaping budget deficit. Greece has moved ahead of schedule into a so-called primary budget surplus, a calculation that excludes interest payments.