LISBON (Reuters) - Portugal's centre-left ruling Socialists lost ground in an opinion poll published on Friday that left it with the narrowest lead in all recent surveys, keeping the ballot wide open just 10 days before a snap general election.
Prime Minister Antonio Costa's party dropped to 37% support, according to the survey by Catolica pollsters, from 39% in the same poll a week ago, while their main rivals, the centre-right Social Democrats, rose to 33% from 30%.
It leaves the Socialist Party further away from a parliamentary majority, which under the proportional representation system equates to between 42% and 45% of the vote.
In October, Costa's two former allies - the Communists and Left Bloc - sided with right-wing parties to reject the minority government's budget bill, triggering the snap election set for Jan. 30.
Analysts say the election alone might not solve Portugal's political impasse as no party or known alliance is likely to win a working majority.
The Left Bloc lost one percentage point, polling at 5%, the same level of support as for the Communists.
Costa has said a new alliance with the two former partners is no longer possible, and signalled he might seek support from smaller parties such as the People-Animals-Nature (PAN). Catolica's poll gave them just 2% support, down from 3% a week ago.
The far-right party Chega would become the third-largest force in parliament, polling at 6%.
The share of voting intentions for the Liberal Initiative party rose one percentage point to 5%, while the right-wing CDS-PP and the eco-Socialist Livre could win 2% apiece, both unchanged.
The margin of error in the Catolica University poll, which surveyed 1,256 people on Jan. 12-18, was 2.6%.
(Reporting by Sergio Goncalves; editing by Andrei Khalip, William Maclean)