HELSINKI (Reuters) - Prime Minister Alexander Stubb said on Thursday that Finland, which shares a 1,300 Km (800 mile) border with Russia, should not exclude the possibility of seeking membership of NATO over the next four years.

Russian air force and naval activity in the Nordic area and pro-Russian insurgency in eastern Ukraine have stirred debate on NATO membership ahead of elections in April. But entry would almost certainly be viewed with suspicion by Moscow which set great store by Finland's non-aligned status in the Cold War.

"I do not see Finnish NATO membership happening in the near future," Stubb, who himself backs membership, told a joint news conference with NATO's Secretary General Jens Stoltenberg.

"It is very important that in the span of the next government we don't exclude the possibility of seeking NATO membership... Second, it would be useful to have a report on pros and cons on possible NATO membership."

An electoral term in Finland is four years.

He said if EU member Finland were to seek membership some day, it would have to have public endorsement.

A poll commissioned by Helsingin Sanomat newspaper on Thursday showed that support for joining NATO remained low at 27 percent, while 57 percent opposed membership. At the same time, 61 percent felt a Russian threat to Finland had increased.

Stoltenberg said he and Stubb had discussed partnership cooperation as well as the Ukraine conflict which began in April and has killed over 5,600 people.

Finland is looking to boost its defense budget and recently signed a plan to extend defense cooperation with Sweden. It has participated in NATO-led missions in Afghanistan and Kosovo.

(Reporting By Jussi Rosendahl; editing by Ralph Boulton)