Defence chief Air Marshal Bruce Ferguson said on Thursday that almost a quarter of army staff with less than six years experience had left to become contractors in the Middle East.
Ferguson added that he had spent the past week with departing staff, mostly privates, corporals and lance corporals.
They said they were leaving because "they wanted the challenge and excitement" of using their training.
"They're leaving because they're getting $200,000 and $300,000 a year to go across and be security guards [in Iraq].
"The salaries are huge. I just can't compete," he told parliament's foreign affairs and defence committee.