He labelled as "out of touch and anti-government" former Australian defence chiefs and diplomats who accused his government of being deceitful about the Iraq war.
In a public statement issued on Sunday, the group of 43 signatories said Australia's involvement had raised the country's profile as a terrorist target.
The government had joined the war "on the basis of false assumptions and deception of the Australian people", the group said in an open letter, echoing similar statements earlier in the year by retired US and British officials.
World has changed
Speaking on commercial radio in Sydney on Monday, Howard said the world had changed since the retirement of the 43 signatories, many of whom had been "long standing critics of the government's foreign policy".
"I reject the claim that we deceived the public," he said. "We believed on the basis of the intelligence advice we had at the time that Iraq had weapons of mass destruction.
"I might point out to my critics that at the time of the military operation there was near unanimous agreement around the world that Iraq had weapons of mass destruction"
Australian prime minister
"I might point out to my critics that at the time of the military operation there was near unanimous agreement around the world that Iraq had weapons of mass destruction."
Cleared by inquiry
The Australian leader also said a recent independent inquiry into intelligence failures had found that on the basis of available intelligence, the conclusion that Iraq had WMDs was more probable than any other conclusion.
The inquiry also found no evidence that Canberra had sought to influence the intelligence.
Howard said every one of the 43 signatories had retired from service well before the 11 September, 2001 attacks on the US, adding: "We're living in a different and more dangerous world and some of the older approaches are no longer quite as relevant."
Australia has been one of the strongest supporters of the US campaign in Iraq, committing about 2,000 troops to last year's invasion and maintaining a force of about 900 in Iraq or the Gulf.