OTTAWA - The Harper government's big-deficit budget that passed the Commons this week could have a hole as big as a white elephant, say opposition MPs.

"There is a gaping hole in the budget," NDP finance critic Paul Dewar said Wednesday.

Dewar and Liberal MP Scott Brison say a shortfall in dubious additional revenues and cost savings amounts to $4 billion this year alone.

That means the actual deficit for the 2009-10 fiscal year could hit $38 billion, they say -- not the $34 billion forecast by Finance Minister Jim Flaherty.

The MPs say Flaherty has booked over $2 billion in asset sales this year without providing a list of what is to be sold or even saying whether any sales will take place.

The other $2 billion comes from departmental efficiency measures that they say also look dubious.

Over five years, the impact of the two measures account for $8.7 billion.

Flaherty acknowledged that asset sales may not occur.

"There'll be no fire sales, you can be sure of that," he said Wednesday. "There may be some sales, there may not."

The budget has similar language. It suggests plans for sales of such things as government-owned lands and buildings will take into account market conditions to ensure fair value: "Assets will not be sold if such sales do not meet these tests."

Given the depressed state of the economy and falling real estate values, Brison said it would be folly for the Conservatives to start disposing of assets at this time.

And he said Flaherty is breaking traditional accounting practices by counting on sales that may not even occur.