THE RAAF's 24 Super Hornet aircraft, plus possibly another 24, are set to play a central role in Australia's air defences for the foreseeable future.

Defence Minister Stephen Smith said it had now become clear to all that the Super Hornets were much more than simply a transition capability.

Initially acquired as a bridging force to cover the gap between the retirement of elderly F-111 strike bombers in 2010 and the delayed arrival of the Joint Strike Fighters (JSF), Super Hornets now operate alongside the JSF in a mixed fleet.

This stems from the acquisition of the Growler electronic warfare version of Super Hornet, launched in 2008 by then defence minister Joel Fitzgibbon and confirmed in August when the government gave the go-ahead to equip 12 aircraft with this very advanced capability.

"So we are now not just looking at Super Hornets as transition, but looking at the longer-term potential of Super Hornets and Growler and Joint Strike Fighters essentially as a mixed fleet," Mr Smith told reporters in Perth.

Announcing the acquisition of 24 Super Hornets in March 2007, then coalition defence minister Brendan Nelson said he envisaged selling them back to the US in 2020 and acquiring a fourth squadron of JSF.

It now appears the RAAF may have only a single JSF squadron by 2020.

Analysts said the Growler acquisition meant Super Hornet was here to stay.

Australia is looking to buy up to 100 of the advanced JSF aircraft as the RAAF's principal combat aircraft from around 2020. So far it's firmly committed to take delivery of just two in 2014. The next 12 are expected to reach Australia around 2020.

JSF has experienced delays and technical problems and may be further delayed. The RAAF'S 71 legacy F/A-18 Hornets entered service from 1985 and were initially slated for retirement from around 2010. Their life has been extended to around 2020.

In an update on Australia's future air combat capability, Mr Smith said the government had assessed a transition plan prepared by defence, leaving its options open except the one to proceed immediately to buy JSF.

Mr Smith said the options including buying 24 more Super Hornets on top of 24 already in service.

Australia was now seeking the latest information on cost and availability of more Super Hornets by way of the US Foreign Military Sales program.

Mr Smith said that did not commit Australia.

"It is being sent so that the Australian government can consider all options in 2013 with the latest and best cost-availability information," he said.

Opposition defence spokesman David Johnston said the government's decision to defer the purchase of 12 JSFs was a politically expedient tactic to help achieve a budget surplus rather than a strategic plan for Australia's future air combat capability.

"In reality, the fact that the US is delaying their JSF purchase would have ensured it could have been more expedient for Australia to have an order filled because production of the aircraft is now up and running," he said in a statement.