The Conservative government's much-touted 20-year defence plan is raising questions about its actual cost.

When Prime Minister Stephen Harper announced the plan earlier this week to equip the military with new ships and planes, he admitted it would have a substantial cost, estimated to be about $20 billion.

But that figure was quickly corrected by Harper's defence minister -- even before the prime minister had a chance to finish his announcement in front of Canadian soldiers.

"Minister (Peter) MacKay just corrected me," Harper said during what appeared to be a carefully staged photo-op for the media.

"He said the total investments we're making in the next generation are closer to $30 billion."

But it turns out that even that figure may not be correct.

Defence officials now say that $30 billion will only cover the annual operating budget for the Department of Defence in 2028 -- after annual increases over the next 20 years. Right now, the annual budget is $18 billion.

On top of the budget increase, military officials say there will be additional money to cover the cost of new equipment. That could mean an extra $45 to $50 billion for combat equipment such as planes, vehicles, and ships.

Critics say such estimates may be too conservative and the real costs could be much higher.

"(The government) can't say whether the cost of the plan is $30 billion or $50 billion or $96 billion," said Liberal House Leader Ralph Goodale in question period Thursday.

"No one in this government has a clue what their defence policy actually is, or how much it will cost.''

The prime minister insists the numbers are quite straightforward. Harper says the bottom line is that the military officials appreciate the monetary commitment.

"They're on the record -- receiving it well and very glad that the decade of darkness under the previous government is over," Harper said in the House of Commons on Thursday.

But critics say the Tories have not provided any details about how additional funds will be spent. And they claim the confusion of actual costs may be a deliberate attempt to hide true costs of the Tory defence strategy.

"When we talk about the size of the investment that they're talking about, which they don't seem to actually have quantified themselves ... I think Canadians would be quite shocked," NDP Leader Jack Layton said.

With a report by CTV's Roger Smith