* Greens made surprise gains in regional vote
* Party draws support from other parties
* Talk of alliance with Merkel persists
By Gareth Jones
BERLIN, Jan 29 (Reuters) - Germany's Greens are on a roll after a big jump in their support in a regional election this month confirmed the growing mainstream appeal of a party once seen as a fringe leftist movement but which now poses a challenge to Angela Merkel.
Worryingly for the conservative Chancellor ahead of a federal election in September, support for the Greens is spreading from the cities to rural areas once dominated by her Christian Democrats.
In Lower Saxony on Jan 20. the Greens won 14 percent of the vote - up from 8 percent in 2008 - by focusing on local concerns about factory farming, nuclear waste and social issues.
Today's Greens - Europe's most successful ecological party - are a far cry from the muesli-munching, sandal-wearing peaceniks of popular mythology.
Long popular among high-earning urban professionals with a social conscience, they are now casting their net more widely by stressing 'conservative values' such as fiscal responsibility.
"We targeted not just our core supporters in Lower Saxony but all those who want real change, including in the rural areas," said Renate Kuenast, a Green leader in the German parliament.
"We have changed over the past decades from a party focused on particular groups, like the peace movement or human rights, because the country has changed and we had to change, to widen our appeal," said the former farm minister.
Their success in Lower Saxony, a sprawling industrial and agricultural hub, has reignited talk of the Greens sharing power with Merkel's conservatives in the autumn, though party leaders play this down for fear of upsetting core supporters.
The Greens won votes in Lower Saxony from all main parties and from people who had not voted in the past.
"We drew support from a very varied array of voters in Lower Saxony - rather more women than men, also from young people, first-time voters and the unemployed," said Katrin Goering-Eckardt, a newly elected Green leader.
Goering-Eckardt, also a leader of the Protestant church, uses sober rhetoric that appeals to conservatives.
"Voters can expect us not to make promises that we cannot keep," she told Reuters in an interview.
In what Spiegel magazine dubbed a "Green revolution" in Lower Saxony, the Greens will join a coalition with the Social Democrats (SPD) to replace Merkel's Christian Democrats (CDU) - a feat they hope to repeat at the national level in the autumn.
It is not the first election upset the Greens have caused the CDU. In 2011, they took control of Baden-Wuerttemberg, a conservative bastion in southwest Germany. They then extended their power when a Green became mayor of the state capital Stuttgart, home to some of Germany's biggest companies.
The Greens have also governed in coalition with the CDU - in Hamburg from 2008 to 2011. More Germans are now asking whether that could happen at the federal level too, especially when the SPD - the Greens' preferred allies - are being dragged down by their unpopular candidate for chancellor, Peer Steinbrueck.
It is an option Merkel may have to consider if her current Free Democrat (FDP) coalition partners miss the 5 percent barrier for entering the Bundestag, the lower house of parliament, in September's vote.
Conservatives and Greens share a belief in fiscal rectitude, European integration and conservation. Merkel took a pirouette towards the Greens by deciding to shut down Germany's nuclear power plants after the Fukushima disaster in Japan and embrace renewable green energy.
John Kornblum, a former U.S. ambassador to Germany, recalls a meeting where senior Greens lawmaker Cem Oezdemir was told "he sounded just like Angela Merkel, to which he replied that he did not disagree with Merkel on many things".
"The old adage was that German chief executives voted for the CDU and their wives and kids voted Green," said Kornblum.
"Supporters of the Greens and the conservatives go to the same restaurants, they often have the same style of life, but they go to different rallies and have different values," said politics professor Gero Neugebauer of Berlin's Free University.
Like most analysts, he believes Merkel is more likely to form a coalition with the SPD - like the one she led in 2005-09 - but said she might prefer the Greens because, as a smaller party, they would be easier to dominate.
"The Greens could be destroyed if they go into coalition with the conservatives," he warned.
Both the SPD and now the FDP have seen their fortunes suffer after entering a Merkel-led coalition. That is precisely what makes many Green voters nervous.
"I fear the Greens would lose their identity if they joined a coalition with Merkel ... I don't know if I could vote for the Greens after that," said Berlin-based neurologist Fabian Klostermann, 44, a lifelong Green supporter.
Leaders like Goering-Eckardt are very aware of such fears.
"We are a progressive, left-oriented party," said Goering-Eckardt, whose East German, Protestant background leads to comparisons with Merkel, a pastor's daughter raised in the east.
In contrast to the CDU, the Greens back same-sex marriage and legal quotas for women in the workplace and oppose plans to pay families who choose to keep toddlers at home rather than sending them to nursery, calling it socially reactionary.
Goering-Eckardt dismissed suggestions that Merkel's renewable energy push could hurt the Greens nationally.
"It is clear in the end that people vote for the original article and that means us. It is a question of credibility."
Some Green supporters were philosophical about striking a Faustian bargain with the CDU, their longtime arch foe.
"It is wonderful that other parties are becoming greener," said actress Barbara Becker. "I just hope the Greens don't become too grey and boring in the process."
Additional reporting by Hans-Edzard Busemann; Editing by Stephen Brown