OTTAWA - Canada's aerospace bosses are warning that thousands of jobs could be at stake if the multibillion-dollar deal to buy the joint strike fighter falls through.

But the industry pressure Tuesday in support of the Conservative government's controversial sole-source deal may have backfired.

With seven chief executives in Ottawa to press the case for the $16-billion purchase of the F-35, Liberal Leader Michael Ignatieff appeared to harden his opposition.

Ignatieff made the issue his top priority in question period, blasting the Harper government for skewed priorities and for abandoning normal procedure.

He said the cost of the fighter is "skyrocketing," and asked: "Why that plane, at that price, without a tender call when there are other urgent social needs for Canadian families?"

Prime Minister Stephen Harper responded that the plane and will create jobs, mostly in Quebec.

But Ignatieff noted the government doesn't even know how much the new fighter will wind up costing given that the estimated price tag keeps rising.

It was precisely the type of exchange the leaders of Canada's aerospace companies were hoping to avoid in coming to Ottawa to plead for political parties to unite on the issue.

The CEOs called the F-35 the "right plane" for the country and said "thousands" of jobs will be created.

Although Canada is only intending to purchase 65 of the fighters, the CEOs said they will be able to bid on related contracts for all 3,000-5,000 planes expected to be built by Lockheed Martin.

And Canadian firms will win their fair share, they insisted, although there are no guarantees.

"We're in the top three countries in terms of aerospace capability," said John Saabas, president of Pratt & Whitney Canada.

"So at a certain point of time you've got to grow up and have confidence in yourself that we can go and win on our own merit."

He noted that Canadian companies have already been awarded close to $1 billion in F-35-related contracts.

The CEOs said uncertainty over whether Canada will buy the jets is making it difficult for companies bidding on contracts, and Canada has only two years to make up its mind.

But the window of opportunity cuts both ways.

Liberal critic Marc Garneau, a former astronaut, called the warning about lost jobs "a little over the top."

The Liberals are looking at another window of opportunity -- the government has until 2013 to review the deal before it is subject to penalties, he explained.

Garneau said the F-35s should be placed in competition with other possible replacement jets to ensure Canada gets the best deal in terms of cost, defence needs, and technology and job benefits.