Prime Minister Kevin Rudd has likened Tony Abbott's language on the Syrian conflict to the children's game of "cowboys and Indians".
The opposition leader said in an interview on Sunday: "It's not goodies versus baddies, it's baddies versus baddies."
Mr Abbott said British Prime Minister David Cameron and former US president Bill Clinton had used similar language on Syria.
"I think the odd use of colloquialism is perfectly appropriate if you are trying to explain to the public exactly what the situation is," Mr Abbott told reporters in Sydney.
In July, Mr Cameron voiced fears that arming Syrian opposition forces could lead to weapons falling into the hands of "bad guys".
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Mr Rudd told reporters in Gladstone on Monday the situation involving the Syrian regime's use of chemical weapons against civilians was not a trivial matter.
"Mr Abbott ... trivialises what is a major foreign policy, international relations and national security question," Mr Rudd said.
"The last time I used the term 'goodies and baddies' was when I was playing cowboys and indians in the backyard.
"I think I stopped doing that about the age of 10."
Mr Rudd said voters who doubted Mr Abbott's ability to handle complex global situations should not vote for him on Saturday.
Mr Abbott said the prime minister had previously used profanity in relation to China after the 2009 United Nations climate change summit.
The opposition leader said he was "ready for the responsibilities of higher office" including foreign policy.
