War on terror lands in Abbott's in-tray

Tony Abbott might be taking a "calm and methodical" approach when it comes to Islamic State extremists.

But there is a growing sense of inevitably that what will start as targeted bombings by RAAF Super Hornets and mentoring by special forces members will expand into a long and expensive war.

Australia has committed 600 troops and up to eight jets, as well as back-up aircraft, as part of the international coalition going into Iraq.

Five years after the end of the last Iraq mission, the prime minister insists that there will be no combat troops directly engaging with extremists on the ground in the "humanitarian" effort.

The only combat, he says, will be air combat by Super Hornets.

So far, US forces have had some success in helping the Iraqi army and Kurdish Peshmerga oust IS troops from key positions in the country's north.

More than 160 air strikes and surveillance by jets and drones, combined with local forces on the ground, have slowly been whittling away at IS-captured territory.

But according to reports from the Kurdish frontline, IS has been a formidable opponent.

Snipers, bombs and booby-traps are among the tricks being used, the BBC reported this week.

Such tactics show the progress of IS won't easily be stopped by bombs dropped by jets.

IS is armed with captured tanks and heavy vehicles, missile systems, anti-aircraft guns and a variety of small and heavy weapons.

US officials believe IS could have as many as 31,000 fighters in Iraq and Syria, with about a third being hardline Islamists and the remainder joining out of coercion.

As many as 12,000 could be from countries other than Iraq and Syria, including Australia, Britain and the US.

The area controlled by IS since fighting began in earnest in early 2013 is understood to be somewhere between 40,000 and 90,000 square kilometres - home to about eight million people.

US President Barack Obama, who will discuss the problem with Abbott and other allies at the United Nations next week, is understandably reluctant to send in ground troops.

"American power can make a decisive difference. But we cannot do for Iraqis what they must do for themselves, nor can we take the place of Arab partners in securing their region," Obama says.

Having largely extracted America out of Iraq and Afghanistan after long wars, the US president knows only too well the risks posed by sending in hundreds of thousands of troops.

While such numbers can be effective in destroying an enemy, they have also been shown to spark new and more violent waves of anti-Western sentiment.

Then there is the cost to the taxpayer.

Abbott says Australia's modest contribution in Iraq could cost about $250 million every six months.

But that is just for starters.

Australia has spent more than $16.5 billion on military operations and overseas deployments since 1998, with Afghanistan accounting for about $9.3 billion.

Labor has backed Abbott's approach so far, but leader Bill Shorten has set out some parameters for how far that bipartisan support will stretch.

He insists there be no "formed up combat units" on the ground.

However, Shorten will come under scrutiny at - particularly from Left members such as Fremantle MP Melissa Parke - as to the merits and legality of the mission.

The Greens say the coalition and Labor are blindly following the US into an open-ended conflict.

But the prime minister says the government has made a "clear-eyed assessment" of the risks and need to protect Australian citizens from IS spreading its tentacles to home soil.

Police raids across Brisbane and Sydney on Thursday, which led to one man being charged with terrorism offences, graphically underlined the PM's message.

The issue is set to dominate parliament, as Attorney-General George Brandis - whose security agencies have been given an extra $630 million - brings in a second tranche of anti-terrorism laws designed to deal with returning foreign fighters.

A third tranche, cracking down on cyber threats, is in the pipeline.

Given the bipartisan nature of national security, the parliamentary debate is more likely to get bogged down in the minute detail of ASIO and police powers, natural justice and privacy than the rights and wrongs of another long and complex war.