THE Coalition may find it harder than it imagines to slash $70 billion from government spending.

A report from the Centre for Policy Development - an independently-funded "progressive" think tank - finds the Commonwealth public service no bigger than it was 20 years ago.

"Our analysis contradicts the prevailing rhetoric about a burgeoning public service," writes the research director James Whelan in the report released this morning. It says about one-third of the public service workforce was retrenched between 1991 and 1999, under the Howard and Keating governments. "Most of these retrenchments happened in the early years of the Howard government when it sacked almost 30,000 staff over three years.

"Although staffing levels have almost returned … to 1991 levels, the … population has increased more rapidly."

The Coalition's official policy is to remove 12,000 public service positions in its first year in office, but revelations it is looking to find up to $70 billion of savings over four years suggest much bigger cuts are likely.

"The cuts will inevitably have a significant impact on the capacity of the public service … ,'' Mr Whelan said.

Coalition shadow ministers have been asked to appear before a meeting of its expenditure review committee today with lists of programs or departments that could be abolished.

Joe Hockey, the shadow treasurer, has told the ABC's Lateline one option would be abolishing the Climate Change Department, which has about 1000 staff.