By Stephen Brown

BERLIN (Reuters) - Angela Merkel's center-left challenger in elections later this year accused the German chancellor on Tuesday of "one-dimensional" leadership in the euro zone crisis and of failing to make Germany more pro-active on the broader world stage.

But Social Democrat (SPD) Peer Steinbrueck, who lags far behind Merkel in polls for the September vote, had few proposals in the main foreign policy speech of his campaign that differentiated him from the governing conservatives.

Like most center-left politicians in Europe, he lambasted Merkel for imposing tough economic reforms on struggling euro zone economies in return for bailouts where Germany, the bloc's biggest economy, foots over a quarter of the bill.

"The content and style of crisis management of this government and Frau Merkel has spread doubt in Europe about whether it can count on German solidarity," Steinbrueck said.

The focus on austerity had pushed some economies into a "death spiral", he said, and created endemic youth unemployment across Europe.

Merkel's insistence on tough structural reforms in heavily indebted Greece, Spain, Portugal, Italy and Cyprus has made her deeply unpopular there, with protesters sometimes portraying her in Nazi uniform or with a Hitler moustache.

Steinbrueck, who served in Merkel's cabinet in her 2005-2009 "grand coalition" government with the SPD, asked in his speech at Berlin's Free University: "Have you any idea what it would be like if Germany had to make savings of 5 percent a year?

"You would not be here, you would be out in the street. But that's what we're doing with these other countries."

NOT AN AMERICAN CENTURY

Steinbrueck echoed the call from opposition in Europe - including Greek leftists - for a new "Marshall Plan" like the U.S. aid that raised Europe from the ashes of World War Two, to make euro zone economies more competitive.

Investing 10 billion euros to create half a million jobs for young people would be just a fraction of the 700 billion euros Europe had dedicated to propping up its banks recently, he said.

Germany could help, Steinbrueck said, by reducing its current account surplus.

Steinbrueck, whose record as a competent minister has been eclipsed by gaffes such as calling two top Italian politicians "clowns", struck a moderate tone but found it hard to overcome the classic dilemma of how to reconcile Germany's economic might with historical European mistrust of its ambitions.

On the one hand he said, Germany "should not lay claim to leadership in Europe" but on the other he criticized Germany for failing to answer calls from the United States or neighboring Poland for a more pro-active Germany.

He chided Merkel's government for letting others take the brunt of military missions like Libya while also saying Germany exported too many arms and that its armed forces did not need drones. Germans have been debating the cost of such equipment.

Steinbrueck struck an awkward balance on the United States ahead of a visit by President Barack Obama this month. He backed EU-U.S. free trade talks while saying: "The United States will no doubt continue to play a dominant role, but this will not be an American century with undisputed U.S. supremacy."

(Editing by Mark Heinrich)