ATHENS (REUTERS) - Greece's radical leftist Syriza party led the ruling conservatives by 3.1 percentage points in an opinion poll conducted after it became clear that a snap election would be called, the pollster Rass said on Saturday.

The survey for Sunday's Eleftheros Typos newspaper was conducted on Dec 29 to 30, after Prime Minister Antonis Samaras failed to have his candidate elected president by parliament.

The poll put support for Syriza at 30.4 per cent against 27.3 per cent for the conservatives of Mr Samaras' New Democracy party, if an election were held now, a slight narrowing from a 3.4 point lead in a previous Rass poll last month.

The election has been set for Jan 25.

In the latest survey, the KKE communist party was third on 4.8 per cent, followed by the centre-left To Potami with 4.7 per cent, and the far-right Golden Dawn with 3.8 per cent.

The Socialist party Pasok, which rules in coalition with New Democracy, polled just 3.5 per cent.

Syriza has led New Democracy in opinion polls for months, but its lead has narrowed in recent weeks.

In the poll, 74.2 per cent agreed that Greece must stay in the euro zone "at all costs", and 24.1 per cent disagreed.

The survey was conducted on a sample of 1,002 Greeks.