The Budget surplus is tipped to reach up to $30 billion, more than double the amount expected last autumn.

While the Finance Branch denies it will be that high, officials recently held a series of special sessions to try to find ways of trimming the windfall.

But a source involved in the discussions said there was ''absolutely no indication as yet'' any of this would go on social spending.

Although social welfare is starting to benefit from last October's boost, it is understood there is still a 20-page list of outstanding funding priorities circulating within Government, much of which will now not go ahead this year.

These include more staff for existing elderly care centres and an expansion of primary education resource centres.

The estimates, which are at the Government Printers, reveal the Social Welfare Department will receive $7.6 billion in the coming year - an increase of 8.2 per cent in real terms, but only about 1.7 per cent more than previously promised by Mr Chris Patten.

The Government says the key spending area is not being given a big new boost out of the latest surplus because it was pledged so much extra in October it may have trouble spending it all.

There is also concern that further big increases would break the Government's rule of not allowing public spending to grow faster than economic growth.

But one top official accused the Finance Branch of tight-fistedness.

''You'd have thought that with a surplus of up to $30 billion they could have spared a bit more for social services,'' he said.

Liberal legislators, who met Financial Secretary Mr Hamish Macleod yesterday to discuss the issue, expressed shock at the prospect of the new Budget surplus not being used to pay for further improvements in social services.

''I'd be very surprised if the increase is as low as that,'' said United Democrats deputy chairman Dr Yeung Sum, warning it would be top of the 13-strong legislative group's agenda in deciding whether to vote against the Budget.

Family Welfare Society director Mr Tom Mulvey called the proposed new increase ''a drop in the ocean''. ''I'm certainly disappointed in view of the size of the surplus,'' he said.

But deputy director of Social Welfare Mrs Rose Goodstadt defended it as adequate.

''We've got some but not all of what we want,'' she said. ''We will always fight for more money to improve the quality of services . . . but we are very happy with a real improvement of more than eight per cent.'' Mrs Goodstadt said the Social Welfare Department already had 500 new projects in the pipeline.

and was rapidly catching up on a backlog of projects that had accumulated over the past two years.

She said money had also been found for further increases in the level of public assistance in the coming year.

A $2.3 billion capital injection was made into the Lotteries Fund last autumn, to fund a 26 per cent real increase in social welfare spending by 1997, aimed at meeting key targets set out in the Government's White Paper.

But voluntary agencies say there is still long list of priority projects waiting for funds to be found.