Defence Minister Peter MacKay, Prime Minister Stephen Harper and the Conservative government need to come clean on the mistakes made in the procurement process for F-35 fighter jets, NDP MPs said Wednesday.

David Christopherson admitted he's being vague about what precisely he wants — refraining from calling for resignations — but says it starts with Harper acknowledging he had a hand in the F-35 file.

MacKay has "got a serious credibility problem," Christopherson said.

"The prime minister has a credibility problem, in fact the entire government has a credibility problem, and it's time for the prime minister to step up to the plate and give Canadians the answers they deserve."

"What we’re now dealing with is a government that’s refusing to come clean. They’re still putting fingers in the dike because the story doesn’t hold together," Christopherson said.

"His cabinet is responsible. His government is responsible. We’d like to know who is accountable. It’s a huge issue."

The auditor general said last week that the government wasn't forthcoming about the cost of the F-35 fighter jet, which defence officials insist is the best choice available. Michael Ferguson also found the Department of National Defence didn't exercise due diligence in choosing the F-35 fighter jet to replace the CF-18 and made key decisions without required approvals or proper documentation.

The government, which announced in July 2010 that it would buy 65 F-35 fighter jets, had internal estimates showing the planes would cost billions more than the $9 billion it said publicly and repeatedly in the House of Commons.

Officials said it would cost $9 billion to buy the jets, plus about $7 billion for ongoing training and maintenance, for a total of $16 billion. The internal estimates, however, indicated it would be closer to $25 billion.

Earlier Wednesday, Liberal MPs Marc Garneau and John McKay said the Conservative government has repeatedly lied and mishandled the attempt to buy the fighter jets, demanding that Harper step down.

"We were asking questions. Why weren’t the cabinet ministers asking questions?" McKay said.

"Stephen Harper is not fit to be the prime minister of Canada. He must resign."

MacKay points to accounting differences

The defence minister chalked up the difference in the government's internal and public cost estimates by arguing they were due to a difference in accounting. On Tuesday, he argued the higher figure includes costs like fuel and pilot salaries, which the government is already spending with the current CF-18 fleet.

MacKay cited segments of Ferguson's report that he said showed Parliamentary Budget Officer Kevin Page had also left operating costs out of his accounting on the F-35s. The budget officer calculated last year that the F-35 costs were higher than the government said, with projections much closer to the numbers Ferguson discovered existed in internal estimates at National Defence.

But MacKay was actually citing the Department of National Defence's own accounting in the auditor general's report, not Page's. DND took out the operating costs for its lower estimate, while Page included them in his own $14-billion figure.

MacKay's office provided a 2004 press release, issued under a previous Liberal government, that indicates the Liberals didn't include fuel or pilot salaries either in cost estimates. The release announced a contract awarded to Sikorsky for CH-148 Cyclone helicopters, which were supposed to be delivered in 2008. The contract was worth $1.8 billion for the purchase, plus $3.2 billion to cover support and maintenance.

A 2010 auditor general report found National Defence hadn't developed full life-cycle cost plans and costs, and hadn't disclosed the full costs. It also found the cost had risen to $5.7 billion, not including personnel and ongoing operating costs, and the delivery has been delayed until 2012.

Christopherson pointed to the government's attacks on Page, arguing it would have been easy to explain a year ago that the two estimates included different costs.

"If it was simply a matter of certain things being included in the [budget officer's] calculations versus other things being included in DND’s numbers, then why didn’t the minister just say so when the parliamentary budget officer brought out his report?" he said.

"That would have been a reasonable answer to the discrepancy. But they didn’t. They went on the attack."

'Disturbing'

The Liberal MPs pointed to the mix-up as proof the defence minister doesn't understand the file, calling MacKay incompetent.

"It’s very disturbing," Garneau said, adding he ran through a gamut of options as to why the defence minister made the error.

"I had to go to the question of, is he trying to pull a quick one on us again, hoping the general public is not going to see this? Or is he not too bright? It went through my mind, I have to admit."

Garneau insisted the government lied when it said it would hold an open competition to choose the company to sell fighter jets to Canada, when it said there was a contract that protected Canadians from escalating costs, as well as about the true cost of the F-35.

Canada has a memorandum of understanding with ally countries to develop the jet, but no contract for the purchase of the jet. But Conservative officials, including Harper, have said there's a contract that protects Canadians from the rising cost of the plane. Harper later said he was referring to the MOU.

"For some purposes we seem to have a contract, and for other purposes we don’t seem to have a contract," McKay said.

Lockheed Martin's F-35 plane is still being developed, and has been plagued by rising costs and delays in production.