The carbon tax, mining tax, Schoolkids Bonus and thousands of Canberra public sector jobs are some of the first on Tony Abbott's hit-list, should a Liberal government be elected in September.

''The Coalition will get spending down,'' Mr Abbott said at a Committee for Economic Development of Australia conference in Sydney on Friday. ''Some of the ways we will do it will be controversial.''

Mr Abbott and his shadow treasurer, Joe Hockey, have said 12,000 public service jobs are in the firing line.

The Commonwealth public sector, which had grown under the Labor government, would be trimmed, Mr Abbott said on Friday.

''There's 20,000 more in the Commonwealth public sector than there were five years ago and there hasn't been a commensurate increase in service delivery or efficiency,'' he said.

But Public Service Minister Gary Gray said Mr Abbott was wrong to suggest the Australian Public service had grown by 20,000.

The APS had grown by about 13,000 places from June 2007 to June 2012, going from 155,424 to 168,580,'' Mr Gray said on Friday. ''Tony Abbott has no public service policy but slash and burn. Today he said there were 20,000 too many people working in the Commonwealth public sector.

''Last week he said he would send public sector workers north, away from the cities and towns across Australia in which they operate.''

Mr Gray said the OECD's Value for Money report last year showed the size of general government employment including states and territories was very low in Australia compared with other countries.

''It is one of the best in the world because Australian public servants are located where they can deliver effective and efficient services,'' he said.

The ACT's three Labor representatives - Kate Lundy, Andrew Leigh and Gai Brodtmann - combined to condemn the Coalition's plan to reduce the public service.

''Tony Abbott has once again confirmed his plans to cut the federal public service, meaning 20,000 people would lose their jobs,'' they said.

''The Liberals' 'positive plans for the future' will impact thousands of public servants and their families, many of whom have young children and mortgages to manage.''

But ACT Liberal Senator Gary Humphries, who has pitched himself as Canberra's champion in his preselection battle with Zed Seselja, says the national capital will be protected during any cost cutting by a Coalition government.

''The Coalition has been completely up front about our plans to reduce the size of the APS,'' he said.

''The Labor Party and the Greens form the government that has been slashing APS jobs under the cloak of darkness.

''At Thursday night's Senate estimates hearings we heard of even more job cuts that are due to hit the APS in a couple of weeks' time.

''As a member of the Coalition frontbench I'll be continuing to work with Tony Abbott and Joe Hockey to ensure the policies of an incoming Coalition government will get the costs of government down but will make sure Canberra's interests are not lost in this process.''