* Salvini quit government in political miscalculation
* Salvini's League is expected to win Umbria regional vote
* Vote is first test for 5-Star/Democratic Party coalition
* Right has scored seven straight regional victories
AMELIA, Italy, Oct 25 (Reuters) - After 50 years governing the green heart of Italy, the centre-left looks set to lose control of Umbria in a regional vote on Sunday that is expected to revitalise far-right League leader Matteo Salvini.
In a political miscalculation, Salvini walked out of government with the anti-establishment 5-Star Movement in Rome in August, expecting to trigger a national election that polls predicted he would win.
Instead, 5-Star hooked up with the centre-left Democratic Party (PD), shunting Salvini into opposition and leaving him looking to upcoming regional elections as a way to exact revenge and confirm that his League remains Italy's top party.
The first such ballot is slated for Umbria, a small region north of Rome that is proving fertile ground for his anti-migrant, anti-tax message amidst public weariness with long-established, leftist rulers after years of economic stagnation.
"This place has traditionally been politically left, but the winds are changing," said Giacomo Vitto, a cheese maker from the town of Amelia, on the southern fringes of Umbria, about 90 km (55 miles) from the capital Rome.
Bank of Italy data show output in Umbria, which has less than 900,000 inhabitants, slumped 15.6% in the decade after the 2007 financial crisis compared with a 5.2% slide across Italy.
"The two main problems we have here, like in the rest of Italy, are high taxes and red tape," said Luca Tomassini, founder and chief executive of digital services company Vetrya, which is based in the Umbrian art city of Orvieto.
Salvini has criss-crossed landlocked Umbria for weeks, promoting his national pledge to introduce a flat-tax rate that many economists say Italy cannot afford, but which the League insists is necessary to revive the sluggish economy with a jolt.
"I bet you a coffee that we will triumph in Umbria. The vote here is also a national test. It is the first vote since the PD/5-Star alliance," Salvini wrote on Twitter on Thursday.
Salvini has hooked up with his traditional allies -- the far-right Brothers of Italy and former prime minister Silvio Berlusconi's centre-right Forza Italia (Go Italy!). They are all backing League senator Donatella Tesei to be the next governor.
Her main competitor is Vincenzo Bianconi, who is heading a civic alliance which for the first time is backed by both 5-Star and PD -- sworn political enemies until their shock decision in August to form a coalition government.
In the wake of that move, and aware that polls gave them little chance of winning if they stood alone in Umbria, they formed a pact to support a joint candidate.
If the model works it might be extended to more important local elections, such as a Jan. 26 vote in Emilia Romagna, a northern region that has more than four times the population of Umbria and which is the historic heartland of Italy's left.
The centre-right has won seven straight regional ballots since the last national election in March 2018. Victory in Umbria would prove Salvini has overcome his August fiasco, but a triumph in Emilia Romagna would be a political earthquake.
"I expect the centre-right will win here, but I don't think Umbria is big enough for there to be repercussions for the government. But if it goes on to take Emilia, things will get really serious," said the Amelia cheesemaker Vitto. (Editing by Crispian Balmer and Edmund Blair)