The study of almost 3,600 schools' budgets, commissioned by the National Governors' Council, indicates that while pupil numbers will rise by up to 150,000, there will be 4,500 fewer teachers in schools this autumn.
The findings, which were presented to education ministers yesterday, will strengthen their case in the public expenditure round which starts next week.
Campaigners for increased education spending said schools had cut back sharply on books, equipment, repairs and supply cover to keep redundancies to a minimum this year.
Next year they would be forced to cut teachers' jobs much more sharply if extra cash was not found, they said.
They estimated up to pounds 1.5bn extra could be needed to restore the effects of the Government's refusal to fund this year's 2.7 per cent teachers' pay rise, and of increases in pupil numbers.
But the study, carried out by the Chartered Institute of Public Finance and Accountancy, showed that while local authority schools were losing 1.4 per cent of teachers this year, staff numbers in opted-out schools were rising by 1 per cent.
Overall, schools were receiving less money for 1995-96 than they were planning to spend, the survey showed.
But while many schools were using up financial reserves in order to protect jobs, it was not clear how many had set budgets likely to plunge them into debt.
Spending on supply teachers had dropped by 13 per cent in a year, on upkeep of buildings by 12 per cent and on equipment and books by 10 per cent. The number of deputy heads employed in schools had fallen by 11 per cent in two years. The number of teachers on temporary contract had fallen by 26.5 per cent in a year.
The National Governors' Council, which was set up last year and which has branches in half the country's local education authorities, believes that more than 40 per cent of primary pupils will be in classes of more than 30 within another year if extra money is not found.
Simon Goodenough, chairman of the council, said he had pressed the schools minister, Robin Squire, to tackle the funding issue. "Governors have obviously done their best to protect teachers' jobs and to make reductions in other areas. But having pillaged these areas this year to save teachers, are they going to be able to do the same next year?"
David Blunkett, Labour's education spokesman, said the report confirmed predictions in a leaked memo earlier this year by the Secretary of State for Education and Employment, Gillian Shephard. "The quality of our children's education is being undermined by Mrs Shephard's weakness," he said.
"She lost the argument last year, and seems set to lose again in this year's budget settlement."
Graham Lane, chair of the Association of Metropolitan Authorities' education committee, said: "No doubt the money saved will be conveniently put aside for illusory tax cuts."
Mr Squire said the report contained valuable evidence. "I appreciate that schools have had to make some difficult decisions this year. But the Prime Minister has indicated that education will be at the top of the Government's priorities."Reuse content