OTTAWA — Prime Minister Stephen Harper shot down Monday a political rival's campaign pledge to scrap a multibillion-dollar purchase of F-35 fighter jets, saying it would "crater" Canada's aerospace sector.

Liberal leader Justin Trudeau had said he would take Lockheed Martin's F-35 out of the running to replace the nation's aging fleet of fighter jets.

Trudeau says that helping develop the aircraft, the apparent front-runner in the bidding process, does not oblige Canada to buy the jets for its Air Force, calling the purchase and lifetime maintenance of 65 F-35 jets for CAN $44.8 billion (US $33.8 billion) a boondoggle.

That would leave three — the Eurofighter Typhoon, the Dassault Rafale and Boeing's Super Hornet — as candidates in the largest military procurement in Canadian history, which has come under fire for spiraling costs and lack of transparency.

"The Liberal party is living in a dream world if they think we could pull out of the development of the F-35 and not lose business," Harper, head of the Conservative Party, said ahead of Oct. 19 elections.

The Tory leader, who is seeking his fourth mandate, pointed to hundreds of millions of dollars in contracts awarded to Canada's aerospace industry since 1997 to develop the stealth fighter with the United States and its allies, and the billions more to come.

But Trudeau said: "What we're seeing now is costs that are skyrocketing [for the] planes so it no longer makes sense."

New Democratic Party leader Thomas Mulcair vowed to reboot the bidding process for the military contracts altogether. Mulcair said he is not necessarily against the F-35s, but is uncomfortable with the process that got Canada to this point.

"It's obvious that we need a new fighter," Mulcair said. "So we're going to try to get this right and try to define quickly what we need and start a process to get us a fighter jet rapidly because our men and women in uniform need that backup and Canada needs that as part of their defense."

Canada had already widened its search for a new fighter jet in 2012 to models other than the F-35 after the procurement came under fire. Opening up the bidding, however, did not preclude Canada sticking with the F-35, which the government and the military still appear to favor.

Canada's fleet of CF-18 fighter jets, built by McDonnell Douglas, which merged with Boeing in 1997, were scheduled to be retired in 2020, but Ottawa has ordered an upgrade to keep them flying through 2025.

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