Ruddock, speaking on public television late Thursday, refused to speculate on the number of people who could be targeted by the new laws, which allow for preventative detention and the electronic tagging of terrorist suspects.
But he said a number of Australians known to have trained with militant groups could be subject to control orders introduced under the laws, which severely restrict the movements of suspects and limit who they can speak to.
"It is quite clear that there are some people who fit the descriptors that are included in the act to make control orders possible," Ruddock said.
"I would expect that a person who has trained with a terrorist organisation - that you believe might still engage in activity which exposes a risk to the Australian community - would have to be considered for control orders and you would do so as soon as you had the legislation in place."
Ruddock brushed off as speculative media reports that up to 80 people suspected to have previously trained with militant organisations could be detained under the new laws.
The laws were drafted after the July bombings on London's transport system that killed more than 50 people.
They were initially approved by all state and territory leaders but rights groups and civil libertarians opposed the draft legislation for giving police shoot-to-kill powers and potentially stifling freedom of speech.
The laws have also been criticised as unconstitutional by legal experts.
Conservative Prime Minister John Howard said Friday he wanted the legislation to come into effect before the end of the year.
"It would be a good idea if it were passed into law during the current parliamentary session and certainly it is desirable that it be in place well before the Commonwealth Games in Melbourne next March," he told ABC radio.
But without significant changes to the laws, which are currently being worked over by state and federal lawyers, they would almost inevitably be challenged, Law Council of Australia president John North said.
"When Ruddock starts slapping anklets on these people, their own lawyers would immediately mount challenges," North told AFP.
North said lawyers were unhappy that the laws forced judges, by making them make control orders, undertake a police function, thereby compromising their independence.
"Lawyers will never be happy if there is a law that ensures people will be arrested... when the state does not have evidence to say they have committed a crime," he said.
Ruddock said he was confident the laws did not contravene the constitution but said he could not rule out a High Court challenge.
"That's always a potential in relation to laws," he said.
"You look at what decisions have been taken by courts before, you look at the provisions of the constitution ... and our laws have to comply with it.
"If people believe the law doesn't, they're entitled to challenge it. It doesn't mean you don't legislate when you have advice that courts have considered like matters and upheld them in the past," he said.
"And that's the situation that we face."