PARIS » A specter is haunting Europe — the specter of socialism's slow collapse.

Even in the midst of one of the greatest challenges to capitalism in 75 years, involving a breakdown of the financial system due to “;irrational exuberance,”; greed and the weakness of regulatory systems, European socialist parties and their left-wing cousins have not found a compelling response, let alone taken advantage of the right's failures.

German voters clobbered the Social Democratic Party on Sunday, giving it only 23 percent of the vote, its worst performance since World War II.

Voters also punished left-leaning candidates in the summer's European Parliament elections and trounced French Socialists in 2007. Where the left holds power, as in Spain and Britain, it is under attack. Where it is in opposition, as in France, Italy and now Germany, it is divided and listless.

Some U.S. conservatives demonize President Barack Obama's fiscal stimulus and health care overhaul as a dangerous turn toward European-style socialism — but it is Europe's right, not left, that is setting its political agenda.

Europe's center-right parties have embraced many ideas of the left: generous welfare benefits, nationalized health care, sharp restrictions on carbon emissions, the ceding of some sovereignty to the European Union. But they have won votes by promising to deliver more efficiently than the left, while working to lower taxes, improve financial regulation, and grapple with aging populations.

Europe's conservatives, says Michel Winock, a historian at the Paris Institut d'Etudes Politiques, “;have adapted themselves to modernity.”; When Nicolas Sarkozy of France and Germany's Angela Merkel condemn the excesses of the “;Anglo-Saxon model”; of capitalism while praising the protective power of the state, they are using socialist ideas that have become mainstream, he said.

It is not that the left is irrelevant — it often represents the only viable opposition to established governments, and so benefits, as in the United States, from the normal cycle of electoral politics.

In Portugal, the governing Socialists won re-election on Sunday, but lost an absolute parliamentary majority. In Spain, the socialists still get credit for opposing both Franco and the Iraq war. In Germany, the broad left, including the Greens, has a structural majority in parliament, but the Social Democrats, in postelection crisis, must contemplate allying with the hard left, Die Linke, which has roots in the old East German Communist Party.

Part of the problem is the “;wall in the head”; between East and West Germans. While the Christian Democrats moved smoothly eastward, the Social Democrats of the West never joined with the Communists. “;The two Germanys, one socialist, one communist — two souls — never really merged,”; said Giovanni Sartori, a professor emeritus at Columbia University. “;It explains why the SPD, which was always the major socialist party in Europe, cannot really coalesce.”;

The situation in France is even worse for the left. Asked this summer if the party was dying, Bernard-Henri Levy, an emblematic Socialist, answered: “;No — it is already dead. No one, or nearly no one, dares to say it. But everyone, or nearly everyone, knows it.”;

While he was accused of exaggerating, given that the party is the largest in opposition and remains popular in local government, his words struck home.

The French Socialist Party “;is trapped in a hopeless contradiction,”; said Tony Judt, director of the Remarque Institute at New York University. It espouses a radical platform it cannot deliver; the result leaves space for parties to its left that can take as much as 15 percent of the vote.

The internecine squabbling in France and elsewhere has done little to position socialist parties to answer the question of the moment: how to preserve the welfare state amid slower growth and rising deficits. The socialists have, in this contest, become conservatives, fighting to preserve systems that voters think need to be improved, though not abandoned.

“;The socialists can't adapt to the loss of their basic electorate, and with globalism, the welfare state can no longer exist in the same way,”; Sartori said.

Enrico Letta, 43, is one of the hopes of Italy's left, currently in disarray in the face of Silvio Berlusconi's nationalist populism. “;We have to understand that socialism is an answer of the last century,”; Letta said. “;We need to build a center-left that is pragmatic, that provides an attractive alternative, and not just an opposition.”;

Letta argues that socialist policies will have to be transmuted into more fluid form to allow an alliance with center, liberal and green parties that won't be called “;Socialist.”;

Winock, the historian, said, “;I think the left and socialism in Europe still have work to do; they have a raison d'etre, and they will have to rely more on environment issues.”; Combined with continuing efforts to reduce income disparity, he said, “;going green”; may give the left more life.

Judt argues that European socialists need a new message — how to reform capitalism, “;recognizing the centrality of economic interest while displacing it from its throne as the only way of talking about politics.”;

European socialists need “;to think a lot harder about what the state can and can't do in the 21st century,”; he said.

Not an easy syllabus. But without that kind of reform, Judt said, “;I don't think socialism in Europe has a future; and given that it is a core constitutive part of the European democratic consensus, that's bad news.”;