The Federal Parliament will start debating the war in Afghanistan later today, nine years after Australian troops were first deployed there.

Prime Minister Julia Gillard and Opposition Leader Tony Abbott will both give speeches today in support of Australia keeping troops in Afghanistan.

It is a debate the Greens have long been pushing for.

Greens leader Bob Brown says the war has claimed the lives of 21 Australian soldiers and thousands of Afghan civilians without bringing democracy to the country.

"The Greens position has been consistent with majority feeling - the troops should be brought home from Afghanistan," he told The 7:30 Report last night.

Ms Gillard says she expects the Parliament to endorse Australia's war effort.

Defence Minister Stephen Smith says there is still a risk Afghanistan could again become a terrorist training ground for several groups including Al Qaeda.

"If we were to leave tomorrow, which is the argument of some, my grave fear is that risk would emerge very quickly," he told Radio National.

"Our way forward is to do what we've been doing, which is to try and train and mentor the Afghan National Army."

Parliamentary secretary Mike Kelly spent 20 years in the army and served in war zones including Iraq, Somalia and East Timor.

He says he supports keeping troops in Afghanistan partly because he is concerned at the consequences if the nation was allowed to collapse.

"I don't support the deployment of Australian troops in harm's way lightly," he said.

"I've seen all of what they are enduring and what they suffer. I've lost friends myself, watched men die, I've seen the full gamut of what is being in Afghanistan, so I don't support that sort of operation lightly.

"I do believe as things stand now it is worth persevering with this mission."

Mr Abbott says the vast majority of Coalition members are comfortable with the commitment.

Coalition frontbencher Greg Hunt says there would be a dangerous vacuum if Australia pulled its troops out, but he also says there should not be a blank cheque to stay forever.

"There has to be progress, such as you saw with Sinn Fein in Ireland, with the Bougainville Revolutionary Army, where you gradually engage more and more of those who are on the margins, whilst pushing out to the extreme margins those who will never engage," he said.

Ms Gillard will open the debate this afternoon, and it is expected to span three sitting days before moving to the Senate.