UPDATE 5-Spain to hold fourth election in four years on Nov. 10

By Elena Rodriguez and Ingrid Melander

* Socialists have struggled to form government since April

* Political limbo has put economic reforms on back burner (Adds reaction)

By Elena Rodriguez and Ingrid Melander

MADRID, Sept 17 (Reuters) - Spain will hold its fourth election in four years on Nov. 10 after rival parties failed to break a months-long impasse in a deeply fragmented parliament, with no guarantee the repeat vote will make it any easier for them to form a government.

Spain, with the fourth-largest economy in the European Union's euro currency zone, has been in political limbo since the Socialists emerged as the biggest party in a parliamentary election in April without enough seats to govern on their own.

Party leaders have spent more time blaming one another for the impasse than negotiating to put together a government, and a flurry of last-minute calls and initiatives on Monday and Tuesday failed to achieve a breakthrough.

"There is no majority (in parliament) that guarantees the formation of a government, which pushes us into a repeat election on Nov. 10," Socialist leader Pedro Sanchez, who has been acting premier since April, told an evening news conference.

Opinion polls show a new election might not end the impasse, with the Socialists winning more seats but still unable to win enough seats in the 350-member parliament to secure a majority on their own.

Although Spain's economy has not suffered greatly, financial analysts say further delays in implementing reforms in areas such as labour and pensions could finally start to bite.

The blame game among main party leaders hit full speed as soon as the snap election was announced, with Sanchez pinning the blame squarely on the opposition and the opposition saying it was all his fault.

"Pedro Sanchez had a mandate to form a government. But he didn't want to. Arrogance and disdain for the basic rules of parliamentary democracy have come before common sense," the leader of far-left Unidas Podemos, Pablo Iglesias, tweeted.

Podemos and the Socialists tried and failed for five months to agree on a government deal.

The leaders of the right-wing People's Party (PP) and Ciudadanos said Sanchez had never really tried to form a government.

Spain has been struggling to put governments together since new parties including Podemos, Ciudadanos and the far-right Vox started appearing five years ago. Before that, PP and the Socialists dominated the country's political landscape for decades.

Spain was forced to repeat the December 2015 election in June 2016 after no single party succeeded in forming a government and repeated attempts to agree on a coalition failed.

There have been no major fiscal reforms since 2015, when then-Prime Minister Mariano Rajoy's majority PP government framed the 2016 budget. After that, budgets were rolled over or approved late for just half a year. (Reporting by Elena Rodriguez and Ingrid Melander; Additional reporting by Belen Carreno, Sam Edwards, Isla Binnie, Paola Luelmo, Emma Pinedo and Jesus Aguadao; Writing by Ingrid Melander and Andrei Khalip; Editing by Mark Heinrich and Peter Cooney)