By Paul Carrel and Douglas Busvine
BERLIN/OFFENBACH, Germany (Reuters) - Branding themselves as the party of reason, Germany's Greens are budding kingmakers in an election in the state of Hesse on Sunday that promises the second thumping in as many weeks for conservative Chancellor Angela Merkel and her ruling allies.
The environmentalist Greens are building on momentum that saw them come second in a state election in Bavaria on Oct. 14. They are carving out a role as Germany's dominant centrist party, which promises to shake up national coalition politics.
Born in 1980 out of the ecologist movement of the late 1960s and 1970s, the Greens are now very much part of Germany's establishment, drawing voters fed up with infighting in Merkel's awkward left-right coalition, mainly over curbing immigration.
"We are the only party that hasn't been driven crazy by right-wing populism," Tarek Al-Wazir, the Greens' half-Yemeni leader in Hesse, told 200 voters during a question-and-answer session on Monday in Offenbach, just outside Frankfurt.
Like Al-Wazir, Hesse evokes diversity: almost a third of its 6.2 million population is of a migrant background. It was also the first state where the Greens entered government, teaming up under Joschka Fischer with the Social Democrats in 1985.
Sunday's election in Hesse, which includes the financial and banking hub Frankfurt, may produce another first for the Greens.
So popular is 47-year-old Al-Wazir - voters prefer him to all other party leaders in Hesse - that there is a slim chance of him becoming state premier after running a campaign focused on pragmatism and his record as the state's economy minister.
"We believe it's important to talk about common sense in the time of Trump," he said at Monday evening's two-hour session, at which he switched easily between touting his policy achievements and fielding questions on national and international issues.
His pragmatic pitch is resonating. In Hesse, opinion polls show the Greens are competing for second place with the centre-left Social Democrats (SPD). Merkel's conservative Christian Democrats (CDU) still lead, but with reduced support.
Nationally, the Greens are polling in second place.
"The realignment of the German party system is in full swing, and the Greens are in pole position to take over the role as the new, truly centrist force," said Carsten Nickel, managing director at Teneo Intelligence, a consultancy.
Polls suggest the incumbent CDU/Greens government in Hesse - a political match-up that itself was unheard of until recently - may lack sufficient support to remain in power, opening up other potential coalition options involving the Greens.
The CDU and Greens could team up with the business-friendly Free Democrats (FDP); the Greens, SPD and FDP could, in theory, join forces - though the FDP is not keen; or the Greens and SPD could work with the far-left Linke.
Under the latter two options, Al-Wazir could be premier. He is not committing to any coalition until after the vote.
"Three-way coalitions will become the norm in Germany," said Jan Techau at the German Marshall Fund of the United States, a think-tank.
In Hesse, the Greens and SPD are tied on 21 percent support, behind the CDU on 26 percent, a survey by pollster INSA for Bild newspaper showed on Tuesday. The far-right Alternative for Germany (AfD) was on 13 percent.
Another poll last week put the Greens just ahead of the SPD.
The polling reflects growing disenchantment with Merkel's conservatives and the SPD - allies in her national government. At the last Hesse election, in 2013, the CDU won 38.3 percent of the vote, the SPD 30.7 percent and the Greens just 11.1 percent.
A poor outcome for Merkel's CDU in Hesse, after her Bavarian CSU allies suffered their worst result since 1950 two weeks ago, would turbo-charge a debate about who succeeds her and when. She has been chancellor for 13 years.
"So far, no obvious challenger has emerged, which is the main reason why she is still in power," said Techau.
But a poor CDU performance in Hesse would embolden Merkel's enemies before her party's annual congress in December, when she will seek re-election as chairwoman. Trying to shore up CDU support, she is making four campaign stops in Hesse this week.
Merkel's fourth and probably final government has already come close to collapsing twice, and a weak SPD performance in Hesse could reignite a debate in the party about whether it should pull out of the coalition.
"The one thing that ties the SPD to Merkel is its fear of virtual extinction in new (national) elections," said Nickel.
The conservative CDU/CSU allies only formed their loveless national alliance with the SPD in March after talks on a three-way coalition of the conservatives, Greens and FDP collapsed. Merkel has ruled three times with the SPD and once with the FDP.
Now the Greens are looking to the Hesse vote to make themselves indispensable to any government. "We want to make sure that nobody can manage without us," said Al-Wazir.
(Editing by Mark Heinrich)