But a firm decision that this option will be taken up has hasn't been made, he said.
"It's early days. I don't want people to run or leap to a conclusion that that is the path we'll go down," he said. "There is some more time. We need to continue to monitor the situation very carefully and closely."
In 2007, Australia ordered 24 Boeing F/A-18 fighters -- originally a McDonnell Douglas aircraft -- as an interim replacement for its General Dynamics F-111 Aardvark tactical strike fighters.
Australia, alongside the United States, was the prime customer for the Aardvark. It had been in service with the U.S. Air Force since 1967 and the Australian air force since 1973. It was phased out by the United States in the late 1990s and by Australia in December.
The F/A-18 is filling the gap left by the F-111 and when the conventional variant of the Joint Strike Fighter, the F-35A Lightning II, arrives.
Smith told ABC "Lateline" news program that the Ministry of Defense had factored delivery date and cost increases into its purchase. But, "we're now running close up to those schedules, particularly on delivery," Smith said.
"So I've made the point very clear that we're now monitoring very closely the delivery timetable. We're also monitoring very closely the cost."
Smith said there would be "an exhaustive risk assessment" done of the current schedule and that will be made available to U.S. officials and to partners in Australia by early next year.
"That will then enable us to start making some judgments about whether we need to make any other plans or take any other action so far as a potential gap in capability is concerned," he said.
Smith also told "Lateline" that the government is reviewing its need for around 100 JSFs as set out in the 2009 Defense White Paper if Australia is to maintain air superiority in the region. The cost would be around $16 billion.
"Our initial order is 14," Smith said. "Any future numbers will be subject to further consideration. Fourteen effectively gives us one squadron. You would want to have more than one squadron of JSFs, but we'll take that step by step.''
A report in The Canberra Times newspaper quoted a Lockheed Martin Australia spokesman saying Smith's position was understandable. Fiscal problems in the United States, especially surrounding the government's debt, raised questions over U.S. Defense Department budget cuts and hardware delivery schedules.
"It would be prudent for any defense minister to keep a very close eye on global developments," the Lockheed spokesman said.
Australia gave final approval in late 2009 for the purchase of the first 14 JSF aircraft, worth $3 billion and to be delivered in 2014. Australia's first operational squadron will be at its air base in Williamtown, New South Wales, and flying by 2018.
The single-seat Lockheed Martin F-35 Lightning, with production at the firm's Fort Worth, Texas, facility, is a single-engine multi-role fighter in three versions -- conventional takeoff and landing, short takeoff and vertical-landing and carrier-based.
Australia's first order of 14 planes is for the CTOL version and includes infrastructure and support required for initial training and testing.
The first test flight of the F-35 was at the end of 2006. The main engine is a Pratt and Whitney F135.
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