Canada is actively rethinking a multibillion-dollar purchase of the Lockheed Martin F-35 Joint Strike Fighter jet or reducing numbers to keep within its present budget, senior officials said.

The F-35 has seen its development costs balloon out of control over the past decade, critics said, and the result is a price which is almost double the original figure.

Present plans call for Canada buying up to 65 jets for $16 billion -- nearly half of that for lifetime maintenance of the aircraft -- but rumblings of dissent over the program have become frequent in Canada.

This week Canada's Associate Minister of National Defense Julian Fantino told Parliament the government had "not as yet discounted the possibility of backing out of the program." Fantino made the comment during a meeting of the House of Commons defense committee, Canadian media reported.

There was no other comment on the potential deal from Canadian officials but Fantino's statement follows Prime Minister Stephen Harper's statement the government is determined to spend no more than the budgeted sum.

A Canadian Defense Ministry e-mail sent to the Star-Telegram newspaper said: "Our position has not changed. We remain committed to the Joint Strike Fighter Program. A budget has been allocated. A contract has not been signed. We will make sure that the Air Force has aircraft necessary to do the job we ask of them."

About $8.5 billion of the budget is to go toward the actual purchase and the rest set aside for lifetime upkeep of the jets.

The F-35 is the key contender for the premier future position in the U.S. Air Force as well as about a dozen other allied air forces.

Canada plans to modernize its air force and retire existing CF-18 Hornet jets, in operation for nearly three decades. The Canadian air force is widely expected to follow acquisition programs pursued by other NATO countries but cutbacks in F-35 orders have already been announced in other member countries.

Cost factors also figured in U.S. military and congressional discussions on the F-35s future role in U.S. air force modernization. The Pentagon considered slowing the production rate of the F-35 to allow more time to fix issues discovered in flight testing.

Despite the cost overruns, the Joint Strike Fighter jet program has drawn strength from a general consensus among procurement agencies that the technology packed in the F-35 is unmatched by any other military aircraft.

However, criticism of the F-35 program centers on lack of current information on the most likely cost per aircraft in the acquisition program undertaken by Canada and other military establishments.

Fantino told the parliamentary committee Canada remained committed to the jet and there was no immediate plan to pull out but admitted the cost per plane was still not known.

Pressed on the likelihood of Canada pulling out, Fantino replied, "That decision will be made if any when those factors are known to us and the decision will be made as to whether or not Canada will actually enter a contract to purchase the F-35."

Canada must start replacing its aging CF-18s within the next few years, latest by 2020.

Canada chose the jet in 1980 after a New Fighter Aircraft competition and began receiving the CF-18 in 1982. Canadian CF-18s supported the North American Aerospace Defense Command patrols and joined combat in the 1991 Gulf War, the Kosovo conflict in the late 1990s and NATO-led operations over Libya last year.

As a possible back-up, Canada may start acquiring armed drones to supplement its current inventory, the National Post reported on its Web site.