The Super Hornet is the backbone of Australia's strike force. Photo / AP

The Super Hornet is the backbone of Australia's strike force. Photo / AP

Australia's plans to replace the air force's ageing strike jets with up to 100 American F-35 stealth fighters are increasingly in question and will be reviewed this year.

The A$16 billion ($19.4 billion) programme already faces delays of up to six years that have forced the Government to spend A$6 billion over the next decade on a stop-gap fleet of Boeing Super Hornets, an upgraded version of the 71 F/A-18 Hornets introduced in 1985.

The Pentagon's decision to postpone orders for 179 of the Joint Strike Fighters over the next five years to save US$15.1 billion has created new uncertainties in Australia and may prompt more Super Hornet orders.

"It is absolutely essential that Australia continues to maintain its air combat capability," Defence Minister Stephen Smith told Parliament.

"The absolutely essential decision for this year is a judgment about whether we are at risk of a capability gap. We will do an exhaustive review of that this year."

Smith said more Super Hornets were "an obvious option".

Super Hornets have greater range than earlier models, can carry more weapons at greater speed and with more manoeuvrability, and have more advanced electronics.

Australia's decision will be influenced by meetings in Washington and Canberra next month at which representatives of F-35 manufacturer Lockheed Martin will be grilled by countries committed to the fighter.

The US attracted Australia, Canada, Britain, Denmark, Norway, Italy, Turkey and the Netherlands as partners, supplementing its own planned buy of more than 2400 aircraft. But repeated delays, cost blowouts - with even more expected from the US postponements - have rattled the partners.

The original price tag for each aircraft has already soared from US$69 million ($83.9 million) to US$103 million.

Turkey has halved its original order, Italy will cut its planned fleet of 131 by as many as 40 aircraft, Canada is considering its future in the programme, Britain will not decide how many it will buy until 2015, and reviews are under way in other countries.

Smith said Australia remained committed to the purchase of two F-35s for tests and trials in the US, and had contracted to buy another 12.

He said F-35 production delays and the ageing of the original Hornet fleet - now undergoing a deep maintenance programme - would cause a gap in the RAAF's combat capability.

Problems had arisen because the US was trying to produce the aircraft before development issues had been solved.

"The schedule for that [Australian F-35s] is now under consideration, just as the United States's schedule is under consideration," Smith said.

"What we will not allow is a gap in our capability, and the decision about the gap in capability will be made in the course of this year ..."

But Parliament's joint committee on foreign affairs, defence and trade has been told by the defence think-tank Air Power Australia and threat simulation company RepSim that buying the F-35 was a mistake.

Experts told the committee that the aircraft was a failed programme with no hope of recovery, offering the wrong product based on outdated threat assessments.

They said the F-35 was inferior to Russian and Chinese stealth aircraft, and vulnerable to advanced radar systems and long-range anti-aircraft missiles.