By Joan Faus

BARCELONA (Reuters) - Crunch elections in Catalonia next week will test the wisdom of the latest political gambles by Spain's Prime Minister Pedro Sanchez, who aims to use the vote to buoy his power nationally but risks inadvertently awakening a dormant Catalan separatism.

Sanchez aims to wrest control of the wealthy region in the May 12 vote from separatists who wield outsized influence over Spanish politics. But if his Socialists perform poorly, the outcome could mangle his fragile parliamentary alliances in Madrid and undermine the stability of his minority government.

It may also revive Catalan separatism seven years after the issue set off Spain's worst political crisis in over 30 years.

Opinion polls forecast a comfortable lead for Socialist candidate Salvador Illa in the election, with the separatist party Esquerra Republicana de Catalunya (ERC), which currently runs the northeastern region, and its more hardline rival Junts appearing neck and neck for second place.

A win would vindicate Sanchez's conciliatory approach to the region's independence movement, which most recently included the offer of an amnesty to Catalan separatists in exchange for their backing of his minority administration in Spain's parliament.

It might also reassure the prime minister that there were no hard feelings among his supporters, after some were troubled by the amnesty offer. Sanchez hopes as well to shore up support across the political spectrum, after many Spaniards were shocked by a five-day break he took from office last month to weigh his possible resignation over what he said was a smear campaign directed against him and his family by right wing opponents.

But if the Socialists are unable to secure the 68 seats required for a majority in the Catalan assembly and have to rely on alliances with other parties, possibly including right-wing rivals the People's Party (PP), their victory could be pyrrhic.

Junts has warned that such a deal with the PP would prompt it to withdraw its crucial support for Sanchez's national government, blocking the passage of legislation in parliament in Madrid and ultimately making it untenable.

Conversely, should separatist parties see a late surge in support and are able to bury old enmities to team up, Sanchez would suffer the double blow of losing the regional contest and seeing a separatist movement gain fresh momentum to push its independence ambitions at a national level, particularly if the victor is the exiled Carles Puigdemont.

Puigdemont, the former Catalan president who fled to Belgium after spearheading a failed independence bid in 2017, is running for Junts and seeks a victorious return. The Spanish arrest warrant he faces over those events is poised to be lifted by the amnesty, expected to come into force in late May or June.

SOCIALISTS ASCENDING

A Basque Country election last month already underscored the influence regional politics has on national government.

The Socialists gained votes in that contest and will return as junior coalition partner to the moderate nationalist PNV, which in turn supports the national government.

In Catalonia, the Socialists aim to replicate a strong showing in the region in last year's national election, when they tallied more than twice the number of votes cast for the next most popular party -- the far-left Sumar -- in a result read as signalling a dampening of pro-independence sentiment.

Their goal this time is to obtain more than 40 seats in the 135-seat regional chamber, said the Socialist campaign head Lluisa Moret. The Socialists hold 33 seats in the current Catalan assembly, level with ERC, while Junts has 32.

At a recent rally, Illa, a calm-mannered former national health minister whose campaign motto is "to unite and serve", barely mentioned Puigdemont and did not even refer to the amnesty that surveys show some socialist voters oppose.

He vowed to move on from a "lost decade" of separatism and focus on concerns such as climate change - a big issue for Catalonia, facing water restrictions after a drought.

"Illa would be a good president because he believes in dialogue. Catalonia is at a moment where it wants reconciliation," said rally participant David Carvajal, 20.

Vicenc Redon, 71, said the amnesty bill should help mobilize voters for the Socialists, but he warned that separatist sentiment could still be rekindled if Puigdemont regains the presidency and launches a fresh drive to break away from Spain.

BUSES TO FRANCE

Puigdemont has said he plans to end his 6-1/2 years of exile in Belgium to attend Catalonia's next swearing-in session even if the amnesty does not remove the risk of his arrest by then.

He is campaigning from over the border in southern France and Junts has arranged buses from Catalonia to his rallies in Argeles-sur-Mer. Puigdemont told Reuters he wanted to connect directly with voters instead of appearing on large screens.

But he conceded it wouldn't be easy to regain the trust of voters disappointed over his handling of the botched 2017 independence declaration, and any fresh independence drive would need "more cunning and better preparation".

Columnist Josep Ramoneda said the election will show whether voters are nostalgic, or fed up with the 2017 legacy.

"It is a total mistake and will unlikely pay important dividends to Puigdemont to come out with a discourse of 'we will do it again'," he said, saying Catalonia had changed.

(Reporting by Joan Faus, editing by Aislinn Laing, William Maclean)