The justice sector has been promised $157 million in new spending, but most of that will be spent on propping up the legal aid system.

The new funding of $157 million over the next two years will be spent mainly on funding shortfalls -particularly with legal aid - and the increased demand of prosecutions.

The legal aid system is undergoing major changes expected to take four years to complete. While that is ongoing, $103 million has been budgeted to the system over two years -$34.1 million for the rest of the 2010/11 year and $69.4 million for the 2011/12 year.

"This extra funding will ensure legal aid services continue to be funded at current levels in the short term, while the Government addresses how to close the $402 million gap between forecast demand for legal aid and baseline funding over the next five years," Justice Minister Simon Power said.

There had been a 55 per cent increase in gross spending on legal aid between 2006 and 2010, he added.

Policy changes to save $138 million were announced last month but there will still be a funding gap.

With the number of Crown prosecutions increasing, $22.5 million will be spent over two years, plus an additional $8 million will be used to target white collar crime.

The Serious Fraud Office has been allocated $8.3 million over two years. SFO Minister Judith Collins said the increase would enable it to increase the number of investigations.

A backlog of cases had been cleared during the past year but the average length of cases was six months.

Mr Power warned the "administration of justice" was not immune from cost pressures, despite the new money.

He said that was part of the reason Justice-sector ministers had ordered changes to criminal procedure, police, courts and corrections services.

Auckland District Law Society president Anna Fitzgibbon last night said it was difficult to know where the new money would be spent. "Whether it's covering criminal legal aid, or families, civil or Treaty of Waitangi claims."

She said the criteria for legal aid had been raised by the current Government so fewer defendants were eligible. She said the legal rates hadn't changed for a number of years.