MADRID (Reuters) - Spain's ruling Socialist Workers' Party would win a general election by a small margin over the main opposition, while a new left-wing coalition is poised to overtake the far right in third place, an opinion poll showed on Wednesday.
A general election is expected to be held in December at the latest, with local and regional votes on May 28 helping to gauge levels of support for each party.
Conducted by the state-owned Centre for Sociological Studies (CIS) in the first week of May, the survey showed the party of Prime Minister Pedro Sanchez garnering 29.1% of the vote in a general election, a drop of 1.3 percentage points compared to the previous month.
It was closely followed by the conservative People's Party (PP) at 27.2%, up 1.1 points from April.
Some polls in recent months have shown the PP ahead, but also well short of a majority.
Sumar, a newly-formed alliance of progressive parties led by Labour Minister Yolanda Diaz, obtained the support of 12.1% of the roughly 4,000 people surveyed by CIS.
It was only the second time that Sumar appeared in a CIS poll after racking up 10.6% of voting intentions last month.
Sumar's result was nearly double that of left-wing Podemos, the junior partner in the coalition government. It remains unclear whether Podemos and Sumar will join forces in the election or run separately.
Far-right Vox fell to fourth place, polling at 10.6% from 11.1% in April, likely hampered by the PP's gains.
(Reporting by David Latona; Editing by Andrei Khalip, Kirsten Donovan)