OTTAWA - Canada should test drive its next fighter plane before it shells out for a program, according to a U.S. defence specialist.

Winslow Wheeler, a procurement authority who spent 40 years on the defence budget in the United States, hammered the Harper government's plan to buy the F-35 fighter jet as part of discussions hosted by the NDP on Tuesday.

"The F-35 is a huge disappointment," said Wheeler, who is critical both of the jet's technology and the costs associated to it.

Wheeler was among four witnesses who spoke at discussions in Ottawa designed to emulate a parliamentary committee even though the Commons is on summer recess.

Other critics, including University of Ottawa defence procurement specialist Philippe Lagasse, say the government needs to etch out a clear defence policy for Parliament and Canadians before it replaces its fleet of aging CF-18s.

"It is not for the military to decide what kind of aircraft they think they need," Lagasse told reporters.

"Ultimately it is the government that tells the military what kind of roles they want the Canadian Forces to play and the military then crafts requirements that reflect those roles."

The NDP says it invited F-35 manufacturer Lockheed Martin and other industry officials to the discussions but the invitations were declined.

In an April report, auditor general Michael Ferguson found national defence officials did not properly inform government ministers about problems with the F-35 program.

Ferguson's report also said the government underestimated expected costs and twisted procurement rules.

In response, the government has set up a new F-35 secretariat who is to play a co-ordinating role as the government moves to purchase new fighters.

"Funding for a CF-18 replacement, including payments to the Joint Strike Fighter program under the MOU (memorandum of understanding), has been frozen until the due diligence is complete and conditions have been satisfied," said Chris McCluskey, a spokesman for Associate Defence Minister Bernard Valcourt.