* AfD won 12.6 pct in Sunday's election
* First far-right group to win seats since 1950s
* Tensions between radicals, moderates have long bubbled (Recasts, adds comment from Gauland, analyst quote, context)
BERLIN, Sept 25 (Reuters) - The leadership of Germany's far right cracked within hours of its electoral success on Monday, when the highest-profile figure in its more moderate wing stormed out of its victory news conference and abandoned its parliamentary group.
Frauke Petry, a 42-year-old chemist, was the most recognisable face in the Alternative for Germany (AfD) during its swift rise over the past two years. But she said she could not stand with an "anarchistic party" that lacked a credible plan to govern, and would sit in parliament as an independent.
The anti-immigrant AfD shocked the establishment by winning 12.6 percent of the vote in Sunday's election after a campaign that channelled public anger at Chancellor Angela Merkel's 2015 decision to leave Germany's border open to migrants.
The result made the AfD the first far-right group to win seats in the Bundestag since the 1950s.
A vocal critic of immigration, Petry served as co-leader of the AfD, but had come into conflict with other senior figures in the party in recent months, saying she understood why some voters were alarmed at some of their radical rhetoric.
She has been less visible as a figure since a surprise decision in April not to run the party's election campaign.
"I've decided I won't be part of the AfD's group in the German parliament but will initially be an individual member of parliament in the lower house," Petry said as she left the party's news conference.
She has said the AfD should be ready to join coalition governments, while other figures said the party should stick to opposition. All established parties refuse to work with the AfD.
Berlin-based political expert Gero Neugebauer said Petry had realised she would not have much influence in the AfD's parliamentary group and may see herself in future as a potential leader of a new group attracting likeminded lawmakers.
Other senior party figures played down her importance.
"It's always a shame when someone very talented leaves the party and Frauke Petry is very talented. But I must note that she wasn't much help recently in the campaign," one of the AfD's top candidates, Alexander Gauland, told Reuters.
Once seen as a radical for transforming the AfD from an obscure group opposed to euro zone financial bailouts into Germany's leading anti-immigration party, Petry had distanced herself from other top AfD candidates before the election.
She had sought to have the party expel Bjoern Hoecke, a senior party official who courted controversy by denying that Adolf Hitler was "absolutely evil" and calling Berlin's Holocaust Memorial a "monument of shame".
Gauland, who replaced Petry in recent months as the party's most recognisable face, provoked outrage during the election campaign by saying Germans should be proud of their World War Two soldiers and Germany's immigration minister should be "disposed of" in Turkey where her parents come from.
Petry said she was aiming to bring about a "conservative turning point" in parliament in 2021, the next time Germany is due to hold a national election.
"I'll do everything I can to achieve that so the sensible ideas the AfD has been working on since 2013 actually become a political reality," she added.
She declined to answer further questions, including whether she would remain the AfD's co-leader, but said the public would hear from her in the coming days.
The party, founded in 2013 by a group of academics opposed to the euro, has long been riven by infighting. Commentators have predicted that its divisions could be amplified by its entry onto the national political stage.
Gauland said neither he nor the other top candidate Alice Weidel nor co-leader Joerg Meuthen knew why Petry left.
Thomas Jaeger, political scientist at Cologne University, said Petry would now need to leave the party, and her decision would likely help the AfD because its parliamentary group would more cohesive without her.
(Writing by Michelle Martin; Editing by Caroline Copley and Angus MacSwan)