About 8 per cent of the Australian Public Service's workforce, or 13,200 staff, are on temporary contracts, of whom about 5000 work in Canberra.

Most government agencies are scaling back their use of these employees to try to cope with steep budget cuts that will come into effect in 2012-13.

Today, the Community and Public Sector Union will present evidence to the ACTU's national inquiry into ''insecure work'', saying the government increasingly uses temps and contractors to cut costs.

However, assistant national secretary Louise Persse said the extent to which the government relied on a temporary workforce was hard to gauge, because it did not report on staff recruited through labour-hire firms.

''We think the community would be surprised to learn that this is an employment practice that governments are favouring. People think a job in the public sector is a job for life; that's just not true.''

The union's submission says that, in Centrelink call centres and parts of the Taxation Office, about 35 per cent of staff are temporary.

Ms Persse said that, contrary to perceptions that contractors and temps earned higher salaries, these workers were often paid less and had fewer benefits.

''They're not all higher-paid consultants; the insecure workforce is much broader than that.''

The union wants the government to be a ''model employer'' that refrains from hiring contractors and offers permanent jobs.

Ms Persse said temps and contractors often cost more in the long term, as the government needed to spend more on recruitment and training.