* Worst post-war result for CDU
* Fears Hamburg rout could spread to other state polls
* Merkel may have to take tougher line in Europe
BERLIN, Feb 21 (Reuters) - Chancellor Angela Merkel's conservatives tried on Monday to move on quickly from a landslide defeat in a state election in Hamburg but the size of the loss could reverberate in six more elections this year.
Merkel's Christian Democrats were swept from power in Germany's second city in the regional election on Sunday with their worst result since World War Two, plunging 20.7 percentage points from the last election there to 21.9 pecent of the vote.
The Hamburg rout could also limit Merkel's room to manouevre in the euro zone debt crisis, where she has demanded economic policy coordination along German lines. Domestic pressure against Berlin paying euro zone bills will rise, analysts said.
"The loss in Hamburg was far worse than anyone had expected," said Dietmar Herz, political scientist at Erfurt University. "Merkel will likely take a tougher line defending Germany's interests to mollify her conservative supporters."
While the CDU had expected to lose Hamburg and its three seats in the 69-seat upper house of parliament, the dimensions of the defeat in Germany's richest city were stunning and could cause turbulence ahead of elections in three states in March.
The opposition Social Democrats took back control of Hamburg with 48.3 percent of the vote, compared with 34.1 percent in the 2008 election. That was enough for 62 seats and an absolute majority in the 121-seat state assembly -- their best result in 17 years.
GLIMPSE OF ABYSS FOR MERKEL
The loss of three seats in the Bundesrat upper house, which represents Germany's states, will make it harder for Merkel's centre-right coalition to pass federal legislation. About half the laws that pass the lower house also need upper house approval.
Hamburg was also the 17th consecutive regional election in which the conservatives' tally declined from the previous vote -- a frightening tailspin that raises nervousness among party officials alarmed about their diminishing job security.
"Merkel will be not able to just sweep Hamburg under the carpet and move on," said Gero Neugebauer, political scientist at Berlin's Free University. "It definitely will have national implications, sending signals for other elections this year.
"The size of the defeat in Hamburg gave Merkel a glimpse of the abyss that she may be staring into at the end of 2011," he added. "If things go badly, she could lose the next six votes and that would make it almost impossible for her to continue."
In 2005, her predecessor Gerhard Schroeder called early elections after his SPD, which had been in a minority in the Bundesrat since 1999, lost a string of state elections that further eroded its position in the upper house.
Merkel is suddenly facing other woes. Her popular Defence Minister Karl-Theodor zu Guttenberg has been embroiled in a plagiarism scandal over his academic thesis, allegations he has dismissed. Rumours that he will resign have swept Berlin.
Merkel's coalition now has 31 of the 69 seats in the upper house after losing Hamburg. There are 24 more Bundesrat seats up for grabs in the next six elections and Merkel's coalition could in a worst-case scenario lose 13 more seats this year.
"We're facing turbulent months politically if the SPD can take the momentum from Hamburg into other states," wrote Bild newspaper columnist Rolf Kleine. "This election win is like a storm flood. The SPD that was in such disarray in 2009 is back."
The CDU got crushed because its candidate Christoph Ahlhaus was deeply unpopular and ran a poor campaign while the SPD challenger, ex-Labour Minister Olaf Scholz, won back traditional SPD voters and moderates by making the economy and debt reduction the focus of his run in Germany's richest state.
The CDU tried to portray Hamburg, where Merkel was born, as a one-off.
"It was mainly about local issues in Hamburg," said Hermann Groehe, CDU general secretary and Merkel's party deputy. "We've got strong chances in other state elections next month."
The SPD hope it will also send a signal to voters before the other state votes, especially in the important southwestern region of Baden-Wuerttemberg in March where the CDU is in danger of losing after six decades in power.
(Editing by Mark Trevelyan)