Australia's apolitical public service is a "precious jewel" that needs nurturing, the outgoing head of ASIO has declared while suggesting a special training college could help the bureaucracy push back against politicisation.

Duncan Lewis, who will retire from ASIO this week after a long public career including time as commander of the nation's special forces, Australia's first national security adviser and ambassador to the EU and NATO, said in the military he had been "lavished" with nine years' worth of high quality training.

Outgoing ASIO chief Duncan Lewis, addressing senior public servants, described the nation's apolitical bureaucracy as "precious jewel". Credit:Alex Ellinghausen

But in 15 years with the public service he had only two three-day periods of training with some of that on management itself.

Mr Lewis said while the training levels of the defence force could not be replicated, the public service should look at ways of boosting its education and training.