Prime Minister Kevin Rudd has announced nearly $4 billion worth of cuts or deferrals to government spending to pay for his promise to bring forward by one year the move from a carbon tax to an emissions trading scheme.

Cuts to the pubic service sector - including 800 senior public servant positions in Canberra - will deliver $248 billion in savings, while several environment programs have been targeted to help offset the cost of the early move to the ETS.

The car fringe benefits tax will be tightened, saving $1.8 billion over the forward estimates.

Mr Rudd's decision to move from a carbon tax to an ETS on July 1, 2014 will cost the budget about $3.8 billion over the next four years, the government says.

''The government has decided to terminate the carbon tax, to help cost of living pressures for families and to reduce costs for small business,'' Mr Rudd said in a Townsville press conference on Tuesday morning.

Treasury modelling shows that in the 2014-15 financial year an average family will be $380 a year better off due to the decision to move sooner from a carbon tax to an ETS, Mr Rudd said.