Public service sources say the department will reduce its workforce by about 440 people, or 48 per cent, by 2014-15.

Staff were told in a meeting this week that the current workforce of nearly 920 full-time-equivalent workers would be cut to about 520 in 2013-2014 and to some 470 in 2014-15.

It follows last week's announcement of about 300 job losses in the department by June 2013 as the government tries to rein in expenditure and deliver a surplus.

But a department spokeswoman said the new figures were just ''one possible scenario'' and a range of options were being considered for ''internal management purposes''. The numbers were based on the department's projected budget for the next three years, which was publicly available in the budget papers.

Affected employees, all of whom are based in Canberra, would be offered ''job application skills training to better equip them in seeking alternative employment''.

''At this stage the staff reductions will be achieved through natural attrition, review of existing contracts, increased opportunities for flexible working arrangements and voluntary redundancies,'' the spokeswoman said.

Earlier this month, the department's secretary, Blair Comley, asked for expressions of interest in voluntary redundancies to reduce staff numbers by a third this financial year.

In a statement to employees, Mr Comley said the cuts were the result of ''a very tight budget situation'', the conclusion of a range the department's programs and the impact of the ''efficiency dividend'' - an annual cut to agencies' administrative budgets.

The Community and Public Sector Union, while unable to confirm the latest job cut figures, said reducing numbers to 470 would be a massive blow for staff and would seriously damage Australia's ability to deal with the impacts of climate change.

National secretary Nadine Flood said that some work in areas such as renewable energy, energy efficiency and industry assistance programs would ''simply not be done''.

''Since the initial cuts were announced a few weeks ago, staff morale has hit rock bottom,'' she said.

''Many staff are voting with their feet, moving to other agencies or leaving the service completely.

''They are passionate about contributing to one of the nation's most pressing issues, but they are growing tired of their increasingly hostile and uncertain environment.''

Federal agencies which have announced plans to reduce staff include the departments of Education (500 jobs), Treasury (150), Resources (100) and Veterans' Affairs (90), as well as the Bureau of Statistics (75), the Fair Work Ombudsman (70) and ComSuper (50).

The Health Department will also shed an unspecified number of jobs, as will many smaller agencies.

Finance Minister Penny Wong has told agencies to try to avoid involuntary redundancies by instead spending less on travel, consultants and advertising.