By David Ljunggren
OTTAWA (Reuters) - Canadians vote on Monday in one of their most unpredictable elections ever, one that could just as easily hand the ruling Conservatives a solid grip on power or leave them so weak they could soon lose office.
The right-of-centre Conservatives, who have governed Canada since early 2006, started the campaign with a healthy lead and said they needed a majority of seats in the House of Commons to let them focus on the economic recovery and keep taxes low.
Over the last two weeks, Prime Minister Stephen Harper has watched his advantage dwindle in the face of an extraordinarily effective campaign by the left-leaning New Democrats, a pro-labour party that has never held power in Canada.
"NDP biggest surprise of campaign," Canada's Globe and Mail newspaper said in a lead election story that questioned whether the Harper government could secure a majority government.
The death of Osama Bin Laden could give a last-second lift to the Conservatives, the party that has staked most on defence and security. The NDP, which has deep anti-military roots, wants to pull Canadian forces out of Afghanistan immediately.
Much will depend on whether the New Democrats, whose organizational structure is less deep than that of the Conservatives or the Liberals, can get its supporters out.
"I want you to create line-ups at the polls, my friends, because we can defeat Stephen Harper," party leader Jack Layton told he told a rally on Sunday.
Opinion polls show that the Conservatives will have the most seats in the new Parliament. But if they don't have a majority, they can only govern with support from other parties, as has been the case since 2006. The Conservatives currently hold 143 of the 308 seats in the House of Commons.
The last polling stations close at 7 p.m. (0200 GMT Tuesday) in the Pacific province of British Columbia, and exit polls are likely to tip a final result soon after that.
The New Democrats promise to increase corporate taxes, limit the amount of interest banks can impose on credit card balances and introduce a cap and trade system to curb the greenhouse gases blamed for global warming.
Harper says the result would be economic disaster at a time when Canada -- the largest single supplier of energy to the United States -- is recovering nicely from the global crisis.
"A New Democrat government means higher prices, smaller pay checks, a weaker economy," he told a rally on Sunday.
The combative prime minister says if he gets another minority the New Democrats and Liberals will quickly unite to oust him and create what he calls a dangerous coalition.
A three-day rolling poll by Nanos Research late on Sunday put public support for the Conservatives at 37.1 percent with the New Democrats at 31.6 percent. The Liberals, who started the campaign in second place, were at 22.5 percent.
The New Democrats and the Liberals are competing for the same centre-left voters and if they split the vote, the Nanos poll shows the result could mean a narrow majority for Harper. That would ensure him a fixed four-year term in power.
An Ekos poll, also released late on Sunday, said the result would be much closer. It had the Conservatives at 33.9 percent, the New Democrats at 31.2 percent and the Liberals at 21.0 percent. No opinion polls are allowed on election day.
(Additional reporting by Pav Jordan and Janet Guttsman)
