Prime Minister Julia Gillard hit back at Opposition Leader Tony Abbott for criticising his country's internal policies before an international audience.

Ms Gillard said on Wednesday she was surprised that there "is a new low in negativity even for Mr Abbott."

"Mr Abbott has reached a new low in negativity by going overseas and criticising this nation's national security credentials in front of an overseas audience," the Australian Associated Press (AAP) as saying.

What's more disturbing, the prime minister said, was Mr Abbott had a hand in the $5.45-billon defence cuts that Treasurer Wayne Swan had presented in the May budget, which was among the federal expenditures scrapped by Canberra to deliver a budget surplus of $1.5 billion by 2013.

Ms Gillard reminded the Liberal leader that he voted in approval of the budget reductions when they were presented at the Parliament.

She was reacting to the earlier statements issued by Mr Abbott while addressing the Heritage Foundation in Washington, in which he expressed his dismay over the Labor-led government's decision to peg its defence spending below two per cent of Australia's gross domestic product (GDP).

The move earned the ire of key U.S. figures, including former State Secretary Richard Armitage, who told The Australian in an interview that he was disturbed by Australia's military budget levelled only to 1.58 per cent of GDP.

"I am a bit concerned about the decline of the Australian defence vote. NATO has an entry price of 2 per cent of gross national product on defence," the former ranking Washington official said.

He would conclude that Canberra was 'free-riding' with the United States, which has declared renewed interest of increasing its presence in the Asia Pacific region after years of relative inactivity.

Mr Abbott said he shared the concerns aired not only by U.S. officials but also by what he claimed as many Australians.

"I do think that it is irresponsible to save money in defence in a way that compromises your military capability given that Australia's military capabilities are not vast to start with," Mr Abbott told his conservative audience.

"The last thing we want to do is to dismay our friends and allies at what is for everyone a difficult time," he added.

But when pressed in a separate interview if he would be willing to return the defence budget to previous levels should he become prime minister, Mr Abbott dodged the question.

"I would want to get the advice of the defence chiefs as to what the impact of this will be on our military capability," the Liberal headliner told Sky News on Wednesday.

On her part, Ms Gillard assured that her government is firmly committed to build up and maintain an Australian military that is "well-resourced."

And that armed forces, she added, is also geared for "cooperation with the United States ... (which) under my leadership has strengthened through our defence relationship."

"We have an alliance that has endured the test of time, and we have taken a new step forward in it with the deployment of marines in Darwin," the prime minister declared, belying suggestions that Australia's credibility was now under questions by its allies.

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