The decision was an unusual step back by Stephen Harper, the prime minister, who has been a strident defender of the purchase despite widespread public criticism of the price. Two cabinet ministers said an independent panel would review a variety of options, including a version of Boeing’s Super Hornet fighter as well as sticking with the F-35, made by Lockheed Martin.
“We have hit the reset button and are taking the time to do a complete assessment of all available aircraft,” Rona Ambrose, the public works minister, told reporters in Ottawa.
The announcement came after the auditor, KPMG, estimated that Canada would spend $45.8 billion to buy and operate the planes over 42 years, the expected life span.
When Peter MacKay, the defense minister, first announced Canada’s plan to buy the F-35 in 2010, he said the purchase price was $9 billion, but declined to provide operating cost estimates. The next year during an election campaign, the Conservatives put the total cost over 20 years at $16 billion.
If Canada were to back out of the project, it would be a blow to Lockheed and the Pentagon, which is counting on foreign sales to help reduce the cost of building each of the planes.
The F-35 was conceived as the Chevrolet of the sky, a radar-evading aircraft that could be built relatively cheaply and adapted to the needs of the Air Force, Navy and Marines.
But almost from the start, development of the planes and their sophisticated gear proved far more costly and difficult than anticipated.
The plane is now projected to be the most expensive weapons program in history, with the Pentagon spending $396 billion to buy 2,443 planes by the late 2030s. The United States is counting on 10 allies to buy at least 700 more.
To meet the Pentagon’s targets of $79 million to $106 million a plane, depending on the model, Lockheed needs to increase its economies of scale by spreading the costs across as many planes as possible. Canada’s hesitancy about the project could add to worries among the allies about the plane’s cost.
This year, economically troubled Italy cut its planned F-35 order by 30 percent. Britain and Australia have delayed decisions on how many F-35s to buy. And lawmakers in the Netherlands are also questioning the jet’s cost.
The Pentagon and Lockheed have stepped up their efforts to reassure those countries and persuaded two others, Israel and Japan, to sign on.
“You have to wonder when a slip becomes a slide with this program,” said Richard L. Aboulafia, an analyst with the Teal Group in Fairfax, Va. “This is not a simple question of a fighter from a new generation all by itself in the market. There is price pressure and there’s a growing cost-consciousness among all customers.”
Until recently, the ruling Conservative Party in Canada swiftly rejected any suggestion that the country not buy the F-35s. Two years ago, Mr. Harper said that critics of the acquisition were “playing politics with the lives of our men and women in uniform.”
But after the office of the Auditor General of Canada released a report in March indicating that the planes would cost much more than the $16 billion the government had indicated, Mr. Harper’s aides began edging away from the program and hired KPMG to produce the new cost estimates.
Ms. Ambrose and Mr. MacKay repeatedly used the word “reset” on Wednesday and avoided questions about what that step would mean in evaluating alternatives. The ministers and officials, however, did make it clear that no decision had been made to start a formal competition among aircraft manufacturers and acknowledged that it remained possible that Canada would stick with the F-35.
The review, Mr. MacKay said, would “ensure that a balance is maintained between the military needs and taxpayer interests.”
Canada’s concerns about the costs of the F-35s come as American officials worry that the F-35’s huge price tag could make it a target for budget cutters in Washington as well. The Pentagon has already slowed the program to fix technical problems and reduce the immediate costs.
Pentagon and Lockheed officials sought on Wednesday to play down the developments in Canada.
Lt. Col. Melinda F. Morgan, a Pentagon spokeswoman, said the KPMG cost estimate for Canada was in line with the Pentagon’s current projections for the cost of the planes.
She said that Canada’s decision to review its options seemed similar to a high-level review the Pentagon conducted in 2010 when problems were mounting with the planes. Top Pentagon officials determined then that they had no alternative that could provide the same capability.
Lockheed issued a statement noting it had worked with Canada’s armed forces for 50 years and looked forward to continuing the relationship.
The KPMG study said that if Canada wanted to stick to the original $9 billion price, it would be able to buy only 55 planes.
Possible alternatives to the F-35 include an updated version of Boeing’s F/A-18 Hornet, called the Super Hornet, and several European models. The Royal Canadian Air Force currently flies CF-18s, a version of the Hornet. While some of Canada’s jets date back about 30 years, Mr. MacKay said Wednesday that the fleet could be kept operational for at least another decade.
In the past, Mr. MacKay and others have emphasized the need for Canada’s next generation of fighters to include the radar-evading stealth technology found on the F-35. But several military analysts in Canada have noted that the country’s air force had not been actively involved in first strikes, where stealth would be most crucial. Others have questioned using the single-engine F-35 for patrols in remote Arctic regions, a primary mission for Canada’s military.
Separately on Wednesday, the government also reduced its estimate of business that Canadian companies were likely to win from F-35 contracts to $9.8 billion from $12 billion.
