Australia is considering buying 18 Boeing-built Super Hornet warplanes for around US$1.6 billion to plug a hole in defence capabilities left by expected delays in Lockheed Martin's F-35 Joint Strike Fighter, said a report.

Australian defence officials plan to raise concerns about project delays and the possibility of a serious gap in Australia's air defences from 2020 onwards when they visit the United States this week, the Australian newspaper said.

Military chiefs were preparing options to plug the gap, including the A$1.5 billion (US$1.6 billion) purchase of 18 extra F/A-18F Super Hornets, adding to 24 of the aircraft bought in 2007 to fill a strategic hole, the paper said, without naming sources, Reuters reports.

Australia plans to buy up to 100 stealthy F-35 Lightning's for an estimated A$16 billion and has so far ordered 14, with the air force's first squadron hoping to be operational by 2018.

But a recent report by a U.S. government budget watchdog found the F-35 program, already behind schedule, was likely to experience additional production problems and cost increases, while also criticising the project's risk management.

Australia's Department of Defence could not immediately comment.

Australian defence chiefs have previously said they are committed to the F-35 purchase, while Lockheed Martin insists that problems in the United States will not derail the 2014 delivery timetable for the first F-35 squadron.

Australia has already begun a multi-billion-dollar upgrade of its military that includes new air defence destroyers, two large amphibious assault ships, helicopters, tanks, long-range cruise missiles and 12 new submarines costing $25 billion.($1 = 0.955 Australian Dollars)