In the latest assault on their Tory opponents, the Liberals accuse the Conservatives of making campaign promises that would drive the country back into a deficit.

"There are a lot of question marks looming over the Conservative plan," Finance Minister Ralph Goodale said Sunday in a written statement.

"The biggest one is what their real agenda is, because this one cannot be delivered."

The Liberals say a Harper-led Tory government would have to either rack up huge deficits or slash programs to realize their vision of a smaller government.

The five-year deficit of $12.4 billion would be through the 2010-2011 fiscal year, according to the analysis, which is based on projections provided by Canadian economists.

The Liberals are also arguing that Harper's plan to redress the so-called fiscal imbalance between the federal and provincial governments could bring the deficit to between $23.4 billion and $53.4 billion over the next five years.

Goodale, in a telephone interview with CTV.ca, contends that Harper has not tried to address how this agenda would be funded.

"That question Mr. Harper has not yet even attempted to answer, and that will have a huge bearing on the bottom line," he said. "Otherwise he is leading the premiers down the garden path, implying there is a solution but knowing privately that he can't afford that solution."

Martin also attacked a Conservative plan to roll back a Liberal tax cut before bringing in its own.

"He's actually going to ask middle-income, low-income Canadians to cut a cheque to the federal government for a tax cut that they have already received ...," he said.

New ads released by the Liberals Sunday claimed the Tories' promises would lead the country back into deficit.

Tories refute Liberal claims

"This is a blatant attempt to scare people again," Monte Solberg, the Tory finance critic said Sunday. "I saw their numbers, and they're ridiculous."

Shortly after the Liberals released their statement Sunday, the Conservatives issued a letter of their own from the Conference Board of Canada, insisting their program is properly costed out.

The statement contends the party platform is fully affordable in each year from 2005 through to 2011.

"In summary, we found that the Conservative Party's economic platform is affordable in each fiscal year from 2005-2006 through 2010-2011," Paul Darby, the board's deputy chief economist is quoted as saying.

"In each year there is enough fiscal room to pay down at least $3 billion a year in debt, as in the (government's) fiscal plan."

The organization, which was given access to the entire Tory platform to conduct its analysis, also found that there is substantial surplus in the Conservative fiscal plan.

"Over the five-year forecast horizon to 2010-2011, the CBoC economic and fiscal outlook suggests that there remains $15.7 billion in unallocated fiscal room, over and above the annual debt payment, which provides further cushion to ensure that deficits do not occur due to adverse economic effects," Darby said.

Conservative national campaign co-chair John Reynolds, who has decided not to seek re-election, called the Liberal claims into question.

"Do you really believe the public will listen to the Liberals when they talk about what a party's budgets are going to do when they couldn't tell their own? They can never tell the surpluses," Reynolds said, appearing on CTV's Question Period.

But Goodale dismissed Reynolds' suggestion.

"I would invite Reynolds, rather than throwing up a smokescreen, to deal with the real question, point out if you can, where there is an error in analysis on the revenue side," he told CTV.ca.

Goodale said all of the revenue projections are based on information provided to the government by 15 independent private-sector economists.

He contends the figures used in the Liberals' analysis come "from the Conservatives' own press releases. This is drawn exactly from their own calculation of what their promises would cost."

Meanwhile, NDP finance critic Judy Wasylycia-Leis came out swinging at both parties, saying neither can be trusted on their figures.

"It's pretty clear that Stephen Harper didn't cost out his plan. And it's pretty rich for the Liberals to criticize them -- given that they've been wrong with their numbers for years," Wasylycia-Leis said in a written statement.

With a report from CTV's Tom Clark