The election comes less than two years after the last one

Mr Harper, who has a lead in the polls, attacked Mr Martin over a corruption scandal in his Liberal Party.

The PM said Mr Harper would roll back civil liberties and welfare policies.

The leaders of two other smaller parties also took part in the debate, which included discussion of the future of French-speaking Quebec.

Poll reverse

Mr Martin's minority Liberal government was toppled in a no-confidence vote in November, after it was confirmed that party members had been involved in a financial kickback scandal.

How many criminal investigations are going on in this government? Stephen Harper

When the campaign started, however, the Liberal Party maintained a lead in the opinion polls.

But polls released on Monday suggest the Conservatives now have a lead of up to nine points.

If the trend continues, Canada could see its first Conservative government since 1993.

'Drive-by smears'

Correspondents say Mr Martin's party has been hard hit by the news that police are investigating an alleged leak by government officials, which appears to have influenced the stock market.

During Monday's televised debate, Mr Harper questioned the Liberal Party's moral authority to govern.

"How many criminal investigations are going on in this government?" he asked the prime minister.

Mr Harper - who lost the 2004 election to Mr Martin - accused the government of "stealing money from the taxpayer".

But Mr Martin hit back, dismissing the allegations as "drive-by smears" and warning that the Conservatives would create a huge budget deficit with their proposed tax cuts.