* Swiss vote in parliamentary election
* Green grouping has chance of coalition cabinet seat
* But low youth turnout, party loyalties may prevail
* Polls closed at midday (Adds polls closing, voter voices)
By Marina Depetris and Cecile Mantovani
BERN, Oct 20 (Reuters) - Swiss voters' concerns about climate change look set to give the environmentalist Greens strong gains in a parliamentary election on Sunday that could dilute the centre-right's grip on power.
A solid showing by the Greens could vault them and allies into the mix for a seat in the grand coalition that has governed the conservative nation for decades. Changing just one member of the seven-seat cabinet would be a political sensation.
Polls closed at midday (1000 GMT). National broadcaster SRF was set to give initial projections, including from the many postal votes, around 1400 GMT.
A Sotomo poll this month for broadcaster SRF showed the right-wing Swiss People's Party (SVP), which won record seats in 2015 amid Europe's refugee crisis, will dip 2.1 points to 27.3% while the Green Party's share will rise more than 3 points to 10.7% of the vote.
The smaller, more centrist Green Liberal Party (GLP) is also expected to advance, bringing their combined strength to a theoretical 18%.
That would place them collectively third behind the SVP and the centre-left Socialists (SP), ahead of the centre-right Liberals (FDP), who all have two seats on the Federal Council that is Switzerland's government.sonos sonos One (Gen 2) - Voice Controlled Smart Speaker with Amazon Alexa Built-in - Black read more
"Climate change: I think it is pretty obvious that is the most important topic of all in our time and age. There is really not any time to lose," said one 25-year-old psychology student from Bern who gave her name only as Anja.
Cabinet seats have been divvied up among the SVP, SP, FDP and Christian People's Party (CVP) in nearly the same way since 1959. The three biggest parties get two seats and the fourth-biggest gets one under the informal "magic formula" system.
In December, the two parliamentary chambers will elect the government, but in the past it has taken more than one national election cycle for that selection procedure to change the cabinet lineup to more closely reflect the results.
Analysts caution against expecting too radical a shift after a campaign that was light on typical hot-button issues such as migration and Swiss ties with the European Union.
GLP founder Martin Baeumle told the Schweiz am Wochenende paper it was an "illusion" to think the Greens and GLP could mount a joint effort to seize a cabinet seat.
He noted differences in the two parties' economic and social policy, scant representation in the upper house of parliament, and the difficulty of ejecting a sitting member of government.
Manuel Buehler, 28, said he liked the GLP for combining liberal policies such as limiting the role of state and keeping taxes low with an accent on the environment.
"We should not (adopt) too many taxes and too many laws but we have to ... achieve our goal to reduce CO2 emissions," the business analyst said. (Writing by Michael Shields, Additional reporting by Emma Farge Editing by Christina Fincher and Dale Hudson)
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