* More than 200,000 take part in rallies
* Anti-nuclear Greens boosted in state vote
* Merkel criticised for nuclear power U-turn
BERLIN, March 26 (Reuters) - More than 200,000 people took part in anti-nuclear protests in Germany on Saturday on the eve of state elections where criticism of Chancellor Angela Merkel's nuclear policies has already given her opposition the edge.
Organisers called it the biggest anti-nuclear demonstration Germany has seen, with police estimating 100,000 turned out in Berlin alone. Hamburg, Munich and Cologne also saw big rallies.
Protesters called for all of Germany's 17 nuclear power plants to be shut down in the light in the nuclear breakdown in Japan, caused by the earthquake and tsunami. "Fukushima is a warning -- close all nuclear plants," was one of the slogans.
The opposition Greens and Social Democrats (SPD), heading for a victory in Sunday's election in the state of Baden-Wuerttemberg which Merkel's conservatives have run for nearly 60 years, denounced her nuclear power U-turn.
After passing a disputed law to extend the life spans of Germany's nuclear power plants last year and calling it a safe source of energy, Merkel's government closed down seven plants last week because of Japan's nuclear disaster and postponed plans to extend the use of atomic energy.
"We are demonstrating here today against a historically bad decision," said Greens parliamentary chief Juergen Trittin, referring to the nuclear power extension last year.
Baden-Wuerttemberg in southwestern Germany is an industrial powerhouse where the Greens have already been boosted by local protests against a major infrastructure project in Stuttgart backed by Merkel's Christian Democrats.
The state is home to one of the seven closed reactors, Neckarwestheim I. The day after Japan's earthquake and tsunami, about 50,000 campaigners formed a 45-km (27-mile) human chain in a pre-planned protest between state capital Stuttgart and Neckarwestheim to demand its demise.
Germany's nuclear plants are run by E.ON(EONGn.DE), RWE (RWEG.DE), EnBW (EBKG.DE) and Vattenfall [VATN.UL].
Late polls show the SPD and Greens each winning 24 percent -- which would give them a 48-43 percent win over the CDU and FDP. With as many as 40 percent of voters undecided, the Greens, normally a junior partner to the SPD, could emerge as the leaders of a state coalition government for the first time.
Merkel has also been criticised by commentators on the right and left for isolating NATO-member Germany on the international stage by abstaining in a U.N. Security Council vote that backed international military action over Libya.
But an opinion poll for Focus magazine released on Saturday said 56 percent of people surveyed supported the stance of the chancellor and her foreign minister, Guido Westerwelle of the Free Democrats (FDP), on the Libyan intervention.
(Additional reporting by Sabine Ehrhardt; writing by Stephen Brown)