By Julien Toyer
MADRID (Reuters) - Spanish Prime Minister Mariano Rajoy's ruling conservative Popular Party has taken a clear lead over rivals in a fragmented political landscape four months before a general election but looks set to fall far short of a majority to govern alone.
An official opinion poll released on Thursday showed the PP with 28.2 percent support ahead of the opposition Socialists (PSOE) on 24.9, both up from the last poll published in May, while the radical leftist Podemos movement and the centrist Ciudadanos lost ground on 15.7 and 11.1 percent respectively.
The findings of the large-scale survey by the state-run Sociological Investigation Centre confirmed both the trend towards political splintering and greater instability, and a modest boost for Rajoy's government from a reviving economy.
With no clear winner emerging, and a September regional vote in Catalonia expected to add fresh divisions, Spain is heading for an unpredictable autumn.
In town hall and regional elections in May, Spaniards swept aside the two-party system that emerged in the late 1970s after the end of Francisco Franco's dictatorship, ushering in an unstable new era of coalition and compromise.
The latest poll confirmed that up to a third of voters back upstart parties like Podemos, Ciudadanos and other splinter groups and are turning their backs on the traditionally dominant PP and PSOE, tainted by corruption and seen as responsible for the worst economic crisis in decades.
While the economy is now expanding at its fastest pace in more than seven years, a stubbornly high jobless rate and rising income inequality are powerful drivers of deep political change.
Although surveys are highly volatile, with one in three voters still undecided, the mainstream duo are seen jointly securing only 50 percent of the vote in the general election due by early December, down from close to 90 percent in the past.
No party is seen winning more than 30 percent, and both PP and PSOE will more likely settle at around 25 percent, making the search for coalition partners necessary in a country with no such tradition in central government.
Thursday's survey showed it may take three parties to form a stable majority as neither leftist Podemos nor pro-business Ciudadanos looks strong enough to be king-maker alone.
Rajoy has fewer coalition options, because of his party's cultural conservatism and hardline support for the unitary state. The PP came top in nine out of 13 the regions that voted in May, but stayed in government in only four of them.
With Rajoy taking a hard line on a new rescue package for Greece, Podemos has suffered in recent weeks from its close ties with Athens' Syriza rulers, falling below 16 percent in voting intentions from close to 25 percent in January.
Ciudadanos has also lost some early momentum and could suffer from Spain's electoral law, which makes it hard for more than three parties to obtain substantial representation in the national parliament.
This leaves the situation wide open after the election.
Recent surveys show Spaniards favor an alliance between the moderate left Socialists and Ciudadanos but such a coalition may fall short of a majority, as would a PP-Ciudadanos pact.
A left-wing "popular front" of the Socialists, Podemos and the smaller Izquierda Unida (united left) is theoretically possible, but both the Socialists and Podemos have said they have too many differences to strike such a deal.
A German-style grand coalition of PP and PSOE would have the numbers but it would come at such a high risk for the junior partner that no political analysts seriously envisage it.
Senior politicians have told Reuters they fear political "chaos" could spread to Spain as a result, a line that Rajoy and Socialist leader Pedro Sanchez are now pushing more openly in a bid to appear as safe bets to worried voters.
This has been reinforced in recent days by a renewed bid by Catalan leaders to frame a regional election on September 27 as a referendum on independence.
Opinion polls show as many as 10 parties could win seats in the regional parliament, with the PP and the PSOE crashing to levels unseen in 30 years in a region that has decided the outcome of most of general elections since the early 1980s.
(Reporting by Julien Toyer, Editing by Sarah White)