"So they're not going on the front line, if you like, in terms of combat," he told the broadcaster.
"As I've made quite clear to people, they would be behind the wire, so I don't think realistically most people would define that as war."
Australia already has 600 troops in the region and is expected to add another 300 about the same time the New Zealanders deploy.
The most likely home base will be in Taji, about 30km north of Baghdad.
Yesterday Mr Key said New Zealand did not have a "realistic option of doing nothing" in the fight against Isis, and he believed he had the public on his side.
He also compared the planned deployment of trainer troops to Iraq with the deployment of non-combat engineers by former Prime Minister Helen Clark in 2003.
"In the past, New Zealand has made significant contributions in the area of training or other activities which I don't think you would see as war," he said yesterday. "Helen Clark sent engineers to Iraq, for instance. That wasn't seen as New Zealand engaging in the war."
He is expected today to give details of a New Zealand contingent to help Australian forces to train Iraqi soldiers to fight Isis, jihadi fanatics who have butchered civilians in Syria, Iraq and Libya.
"We are just doing that, training Iraqi forces to stand up to Isil, to combat Isil but it is not New Zealand at war. It would be New Zealand providing services to assist others."
Helen Clark ordered two rotations of 61 Defence Force engineers to spend a year in Basra from September 2003 in a strictly non-combat role, after the US, Britain and Australia invaded Iraq in March that year.
Mr Key believes that a majority of the public backs some contribution - a One News Colmar Brunton poll last night put support at 48 per cent compared with 42 per cent opposed and 10 per cent who did not know.
He believed the public thought the same way about Isis as the Government.
"Isil have demonstrated through its actions over the past year or so just how barbaric they are and New Zealanders would expect us to do something to try and stand up to them."
There would be a range of views on what that should be. Last night, he was planning to call Australian Prime Minister Tony Abbott and Iraqi Prime Minister Haider al-Abadi about the Cabinet decision yesterday.
Mr Key will outline the details of the deployment in a ministerial statement to Parliament at 2pm.
Other leaders will be given the opportunity to debate his statement but a vote is not required. It is an executive decision taken by the Cabinet and, in any event, Mr Key would not be able to pass a vote sanctioning the deployment until or unless National wins the Northland byelection on March 28. It has the support of only Act.
Helen Clark had a vote in 2001 on the deployment of the SAS to Afghanistan - in the knowledge that it would overwhelmingly pass.
Mr Key said the New Zealanders would have the capacity to defend themselves but would not accompany Iraqis in combat. "We are not going to be involved in combat - that's an absolute assurance."
He said that if Iraqis were being overpowered down the road "they could not go and assist that".
Mr Key, who has previously said involvement in Iraq was "the price of the club", said that his comments had been misinterpreted and that by "the club", he had meant the 60 or so countries that were helping in the coalition against Isis.
- additional reporting NZME. News Service
