* Polls see Social Democrats and Greens taking power * CDU has run Baden-Wuerttemberg for nearly 60 years
* Japan nuclear crisis boosts environmentalist protest
By Hendrik Sackmann
STUTTGART, Germany, March 24 (Reuters) - Economic prosperity and five decades of history may not be enough to prevent Chancellor Angela Merkel's conservatives losing power in one of Germany's biggest states on Sunday.
The industrial state of Baden-Wuerttemberg is leading Germany's recovery from recession, but the chancellor seems unable to stop a host of outside factors -- Japan's nuclear crisis, Portugal's debt woes, Libya -- eroding CDU support.
The election is the most important of seven state polls this year, and defeat for the CDU after 58 unbroken years in power in Stuttgart would be a huge blow to Merkel as she fights to shore up her political authority.
A Forsa poll published on Thursday predicted victory in the state of 11 million people for the combined Social Democrats (SPD) and Greens, coming in 5 points ahead of the conservatives.
It predicted Merkel's Christian Democrats (CDU) would get the most votes but not enough in combination with their weakened Free Democrat (FDP) partners to outgun the centre left.
Merkel was already facing failure in the state when the Libyan revolt, Japanese earthquake and nuclear breakdown came out of the blue to present her with huge policy headaches.
"Not every global political event is an issue in a state election," Merkel said this week as her party tried to decouple the international events from local issues in the state.
"The nuclear debate is helping the Greens now but the CDU and FDP will still win because Baden-Wuerttemberg is the most successful region in Europe," said CDU national parliamentary chief whip Volker Kauder, who is from the state. "People here won't vote out those who made the state so successful."
Merkel last week suspended a government agreement prolonging the life of the nation's nuclear power stations as Japanese engineers struggled to avoid a nuclear meltdown after the quake.
Local and nationwide polls show Merkel's response is undermining her and widening the centre left's established lead.
BIG GREEN SHADOW
At state level, Forsa's poll suggested that nuclear power and concerns over a railway project in the state capital Stuttgart topped voters' concerns -- boosting the anti-nuclear Greens and their likely SPD coalition partners.
Conservatives in a state that makes Mercedes-Benz and Porsche cars are annoyed by Merkel's nuclear moratorium, making it look like a doubly risky electoral tactic.
Thorsten Faas, a politics professor at Mannheim University in Baden-Wuerttemberg, said the media prominence of the nuclear story could easily sway the high number of undecided voters -- 40 percent in the Forsa poll -- towards the Greens.
While the Greens might not do well enough to win their first state premiership, their gains suggest a changing landscape.
"A few years ago it would have been impossible to imagine Baden-Wuerttemberg with a non-CDU state premier. But things have changed here and the Greens especially have grown," he said.
He said losing Baden-Wuerttemberg could be disastrous for the CDU, comparable to the SPD's loss of its stronghold of North Rhine-Westphalia in 2005, which forced then-chancellor Gerhard Schroeder to call a national election that put Merkel in power at the head of a CDU-SPD "Grand Coalition".
Merkel's future would depend on whether CDU bigwigs blame her, or CDU state premier Stefan Mappus and the FDP instead, and if any rival emerges in the CDU -- a rare commodity so far.
Commentators on the right and left, such as the former Greens foreign minister Joschka Fischer, say she isolated Germany on the international stage by breaking with NATO to abstain on the U.N. vote on military action over Libya.
This risks reversing the political recovery in recent weeks of her foreign minister, FDP chief Guido Westerwelle, who had been gaining ground with some deft diplomacy in North Africa.
The FDP did well in Hamburg last month but lost its place in Saxony-Anhalt's assembly when the CDU just clung to power. If it fails in Baden-Wuerttemberg and does not win a seat in less strategic SPD-run Rhineland-Palatinate the same day, its leader could also face the music in April's party convention.
Before Japan and Libya, Merkel's main concern had been isolating the vote from the euro crisis by taking a tough line on bailout funds for the likes of Greece, Ireland and maybe Portugal to assure taxpayers she will not waste their money.
EU stalling on bailout funds could spare her bad headlines from this week's summit in newspapers critical of more euro zone largesse, but she has already been accused of "Zig Zag Politics" on nuclear and foreign policy by mass-circulation Bild.