OTTAWA - A top defence department bureaucrat jumped into the dogfight Thursday over the cost of the F-35 fighter program, accusing Parliament's budget watchdog of pulling numbers out of thin air when he tried to tally up what the controversial program will cost taxpayers.

The government says buying 65 F-35 stealth fighter jets will cost about $16 billion spread out over 20 years. Parliamentary Budget Officer Kevin Page, in a report his office released last week, said it will cost nearly double that, or $29.3 billion spread out over 30 years.

On Thursday, Dan Ross, the assistant deputy minister for procurement at the Department of National Defence, said Page's figures make no sense.

"We can't match his number. It doesn't match anything we've seen," said Ross.

Ross has asked for a meeting with Page to sort out how he arrived at his conclusions.

Ross also said Page's staff made an addition error in their report that overestimated the cost by more than a billion dollars.

The cost issue is at the heart of objections by federal Liberals, who want an open competition for the new fighter contract.

The Conservatives say the F-35 is the only jet that can meet the needs of the air force.