The leader of the Nationals yesterday delivered his party's reply to the 2008-09 state budget, which was unveiled on Tuesday.

Mr Stoner said the budget continued a concerning trend of costs to government rising faster than revenues.

"Over the forward four-year period, revenues are projected to increase by 4.4 per cent and expenses are projected to increase by 4.5 per cent, leaving a gap of $160 million," he told parliament.

"Whether it is a $45 billion government budget or a $450 weekly household budget, one principle always holds true – if you spend more than you earn then you will need to borrow to balance your budget, and if you can borrow no further then you will need to start to sell assets."

The 2008-09 budget sets out a plan to almost double state debt by 2012, from $22.2 billion to $41.7 billion, to fund a major capital works program.

The government is also pushing forward with a plan to offer long-term leases for the state's electricity generators and sell off state-owned retail energy firms, despite union opposition.

"Let me issue this stark warning. The premier's proposal to sell all of NSW's electricity assets is the tip of the iceberg," Mr Stoner said. "... if he cannot get his house in order, if he cannot impose some financial discipline, then this government will continue to be forced to sell taxpayers' assets.

"Whether it be Sydney Ferries or the electricity transmission grid – the one thing we can be sure of is there will be more sales to come."