A quarter of respondents to the survey were unable to say whom they would vote for. In November, just 15 percent were undecided.

The conservative National Coalition Party's Sauli Niinistö remains by far the most popular candidate, with 40 percent backing. However his support declined from 49 percent in November.

That makes it less likely that he will earn an outright majority of votes in the first round of the election, which would eliminate the need for a run-off.

The battle for who will be Niinistö's opponent in a likely second round remains too close to call. Four contenders have similar levels of support. The survey results suggest that Centre Party candidate Paavo Väyrynen may have marginally strengthened his second-place position with support for Timo Soini of the Finns ebbing slightly. Pekka Haavisto of the Greens may have surpassed the SDP's Paavo Lipponen, leaving the ex-premier in fifth place out of the eight candidates.

Väyrynen's support was measured at nine percent in December (eight in November), with Soini at seven percent (down from eight), Haavisto remaining steady at six and Lipponen slipping to five (from seven).

The other three candidates have the backing of just two to three percent of voters.

Clear knockout for Niinistö in round two?

In a second-round runoff, the poll shows Niinistö winning decisively against either Väyrynen (82 to 18 percent) or Soini (83 to 17 percent).

The polling agency Taloustutkimus interviewed nearly 1,700 Finns between late November and mid-December.

It rates the margin of error at 2.5 percentage points -- meaning that the differences between Niinistö's challengers are mostly statistically insignificant.