BRAMPTON, Ont. — Stephen Harper says he stands by his cost estimate for the F-35 stealth fighters.

The prime minister made the declaration Wednesday, even though the Pentagon's latest estimate for the version of the fighter jet Canada intends to buy is double what the Conservative government has projected.

In defending the $9-billion sticker price, Canada's Defence Department has said it will pay between US$70 million and US$75 million for each aircraft, a figure that the parliamentary budget officer has disputed.

The Pentagon recently projected it will pay $151 million for each aircraft for the F-35A, the standard runway take-off and landing version of the fighter bomber.

The U.S. Government Accountability Office, crunching numbers earlier this month, pegged the cost between $110 million and $115 million per plane. But defence experts said that report doesn't take into account recent changes to the program.

Harper says there are cost increases in the U.S. program that have no impact on Canada and he's confident of the numbers he's been given by officials.

"All the information suggests we're well within the cost estimates for these jets, which we need," Harper said during a campaign stop Wednesday.

Canada's CF-18 fighter jets, which the Joint Strike Fighter is meant to replace, will soon reach the end of their service life, he warned.

"We've been involved in a 15-year procurement process and all of the information we have from our aerospace industry, from our National Defence officials is that these costs are well within our estimates and well on track."

Under the arrangement with Washington, allies participating in the F-35 program gather annually to list the number of aircraft they intend to buy in any year. The Pentagon then negotiates the price with aircraft-maker Lockheed Martin.

In theory, the more aircraft that are built, the lower the unit cost.

The agreement signed by Ottawa last summer binds Canada with its allies. If one country decides to pull out or not purchase in a particular year, as Turkey has signalled it will do, the cost per aircraft goes up for the countries remaining in the pool.

The F-35 program has seen massive cost overruns, which have alarmed lawmakers in the U.S. The Pentagon's program is estimated to cost $386 billion, almost double what was initially proposed.

The Harper government has fought a pitched battle with the opposition parties and the parliamentary budget officer over its figures. When the purchase of 65 stealth fighters was first announced, the Conservatives said the price tag was $9 billion for the aircraft and up to $7 billion more for 20 years' worth of maintenance.

Kevin Page, the parliamentary budget officer, questioned that math in a recent scathing report, which pointed out National Defence had not done its own independent analysis of the numbers provided by Lockheed Martin.