And the government has been urged to come clean on cuts to services after successive years of public service cuts, efficiency dividends and staff reductions.

Prime Minister Kevin Rudd said on Tuesday that Labor's decision to ''terminate'' the fixed price would be budget neutral and leave the average family $380 a year better off under his plan to move Australia to an emissions trading scheme a year earlier.

As well as public service job cuts, the $3.8 billion, four-year cost of fast-tracking the carbon pricing regime means Labor will make changes to fringe benefits tax breaks and wind back some clean energy programs.

Opposition leader Tony Abbott said by bringing forward changes by 12 months, Mr Rudd hadn't actually terminated the carbon tax.

''He's not the terminator, he's the exaggerator,'' he said.

Treasurer Chris Bowen said the ''preference'' was to cull the executive and senior executives through natural attrition but did not rule out forced redundancies.

The new cuts, expected to be 400 jobs, come on top of reductions of 400 announced by Finance Minister Penny Wong in the federal budget.

CPSU national secretary Nadine Flood warned members to brace for forced redundancies. More than 60 per cent of the service's executive level workers are Canberra-based and more than 75 per cent of senior executives work in the capital.

The Treasurer said in Townsville on Tuesday that he was looking to save $248 million over the forward estimates period with deep cuts to the bureaucracy's senior ranks with the cuts ''exclusively'' at executive level and above.

The savings are on top of $148 million announced in the budget to be achieved over four years through staffing cuts and greater efficiencies in IT procurement.

A 2 per cent cut to the cost of the bureaucracy's senior ranks is thought to equate to about 800 jobs but departments are being told they are free to choose how they achieve the savings.

''These changes will be exclusively in the executive and senior executive ranks of the public service,'' Mr Bowen said.

''There are approximately 44,500 positions in those ranks and that will reduce in time by about 800 positions.

''These positions have grown by about 29 per cent over a period when the general public service has grown by about 6 per cent and all the calculation and all indications would indicate that this would be an appropriately and measured and balanced step over time.

Asked if most of the job losses would be in Canberra the minister replied: ''You would expect them to be, yes.''

''Obviously the preference is for natural attrition over time,'' Mr Bowen said.

Former Public Service Commissioner Andrew Podger said there was a good case for addressing the ''classification creep'' that has seen the huge growth in executives and senior executives in the service.

But the now professor of public policy at ANU said the successive rounds of cuts could not be made without reductions to service levels.

''My main concern is that this is in addition to everything else, it's in addition to the cuts in the budget, in addition to the continued efficiency dividend and the fact that agencies have not been fully indexed for pay increases,'' Professor Podger said.

''So you add that all up and you cannot have those cuts without also affecting the level of services to the public.

He called on both sides of politics to take responsibility for declining service levels.

''Reducing services to the public is not necessarily a bad thing to do when you need to prioritise but my main concern is that the government, and indeed the opposition when it proposes cuts, should stand up and say 'we are going to reduce services' and take responsibility for it.''

Ms Flood said: ''We're disappointed to see 400 executive jobs cut, on top of the 400 already announced in the May Budget.