* Change comes after Greens gained in state vote
* Party had been big backer of keeping plants open
* FDP is junior partner in Merkel's coalition
(Recasts with background, quotes and reactions)
By Thorsten Severin
BERLIN, March 29 (Reuters) - Germany's Free Democrats, junior partners in Chancellor Angela Merkel's coalition, said on Tuesday they want to shut down permanently seven older nuclear plants temporarily idled after Japan's nuclear disaster.
The liberal FDP had been a driving force behind a law to extend the use of nuclear power. Deputy leader Christian Lindner announced the U-turn after the coalition lost power in a state vote on Sunday where the anti-nuclear Greens won record support.
Germany has a total of 17 reactors. Merkel's centre-right government passed legislation last year to extend the lifespan of the 17 by an average of 12 years beyond a previous 2022 cut-off date. The FDP has been strongly pro-nuclear until now.
"We've got to reach an agreement with the utilities in which the old reactors won't be put back on line," said Lindner, tipped as the possible next FDP chairman if Foreign Minister Guido Westerwelle relinquishes the party leadership.
"We want to move quickly to change the energy policies."
While other leaders in Merkel's Christian Democrats added their voice to a chorus calling for Germany to make a quicker exit from nuclear power, some conservatives such as parliamentary whip Volker Kauder remained firmly opposed.
"We're going to go further than even the Social Democrats and Greens could ever imagine," said another senior CDU lawmaker, Norbert Barthle, referring to the centre-left parties that passed a 2000 law to phase out nuclear power by 2022.
Merkel said on Monday her view on nuclear energy had changed after Japan's earthquake triggered a nuclear crisis, but she did not say concretely if the existing law would be changed.
Environment Minister Norbert Roettgen, however, said Germany should shut its nuclear reactors faster than planned because the loss on Sunday of the conservative stronghold Baden-Wuerttemberg -- in a vote where Japan's nuclear disaster played a major role -- showed the public wanted a quicker exit.
Merkel's government last year scrapped the law passed by the red-green coalition even though polls showed most Germans opposed that policy shift.
But after the Japanese nuclear disaster, Merkel retreated and declared a three-month moratorium on the extensions.
She also temporarily shut seven nuclear plants built before 1980. The policy flip-flop upset her party's business wing and failed to impress voters in Baden-Wuerttemberg, some of whom saw it as an election ploy.
(Writing by Erik Kirschbaum; editing by Paul Taylor)