Francois Hollande was sworn in as president of France on Tuesday with a solemn vow to find a new growth-led strategy to end the crippling debt crisis threatening to unravel the eurozone.

After brief ceremonies and a rain-lashed walkabout, the 57-year-old Socialist headed to Berlin to confront Chancellor Angela Merkel over their very different visions as to how to save the single currency bloc.

Hollande's plane was hit by lightning shortly after takeoff and returned to Paris, but the president left again shortly afterwards in a different jet.

"Europe needs plans. It needs solidarity. It needs growth," Hollande told dignitaries at his new home, the Elysee Palace, renewing his vow to turn the page on austerity and implicitly underlining his differences with Merkel.

"To our partners I will propose a new pact that links a necessary reduction in public debt with indispensable economic stimulus," he told the assembled Socialists, trade unionists, military officers, churchmen and officials.

"And I will tell them of our continent's need in such an unstable world to protect not only its values but its interests."

Hollande also named his new prime minister, Jean-Marc Ayrault, a 62-year-old longtime Hollande ally and the head of the Socialists' parliamentary bloc, who was tipped as favourite.

Ayrault's new cabinet will likely hold its first session on Thursday after which the Socialists turn to their campaign to win a parliamentary majority in June's legislative elections -- a key test for the party after Hollande's win.

The new president was welcomed to the Elysee Palace by his predecessor Nicolas Sarkozy, who led him to the presidential office for a private head-to-head and to hand over the codes to France's nuclear arsenal.

Hollande ushered Sarkozy to his car for a final farewell, outgoing first lady Carla Bruni exchanging kisses with Hollande's partner Valerie Trierweiler, elegant in a dark dress and vertiginous heels.

Hollande then signed the notice of formal handover of power -- becoming the seventh president of the Fifth Republic and only the second Socialist.

No foreign heads of state were invited to what was a low-key ceremony for a post of such importance, leader of the world's fifth great power.

After the swearing in, Hollande rode up the rainswept Champs Elysees to the Arc de Triomphe in a modest open-topped Citroen DS5 hybrid, a symbolic break with the flashy style of his predecessor.

Soaked to the skin, Hollande laid a wreath at the Tomb of the Unknown Soldier and shook hands with veterans before greeting the sparse crowd of wellwishers who braved the bad weather.

He then visited Paris City Hall, a swearing-in day tradition for the French president, for a ceremony presided over by Socialist Mayor Bertrand Delanoe and attended by the capital's elected and religious officals.

But the real work was to begin after Hollande's second plane arrived for tense talks with Merkel, the leader of Europe's biggest economy and France's key ally.

Merkel was a Sarkozy ally and the architect of the European Union's fiscal austerity drive. Hollande opposed the speed and depth of the cutbacks demanded by Berlin, and wants to renegotiate the eurozone fiscal pact.

Germany is committed to budgetary discipline, and Merkel has repeatedly insisted since Hollande's election that the pact, signed by 25 of the 27 EU countries and already ratified in some, is not open to renegotiation.

But observers say there is room for compromise, with Hollande likely to agree to additional stimulus measures without a rewrite of the pact.

Symbolising the rising pressure on the heads of Europe's two largest economies, Greece was on Tuesday facing new elections after talks failed on forming a government in the debt-wracked country.

The leaders will have to reassure worried markets they can work together after new figures showed France's economy stagnant, with statistics agency INSEE saying it recorded no growth in the first quarter of 2012.

The agency also revised downward the growth figure for the fourth quarter of 2011, to 0.1% from 0.2%, while maintaining that the economy grew by 1.7 percent overall in 2011.

After the talks with Merkel, Hollande heads to the United States where he is to meet President Barack Obama at the White House on Friday ahead of back-to-back G8 and then NATO summits.

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