They will warn him they cannot deliver his literacy and numeracy targets because the present curriculum is too broad and distracts them from teaching the basics.
The heads' demand to free the primary curriculum, to be made at their annual conference in Scarborough next week, will be the first test of Mr Blunkett's new deal for education.
Mr Blunkett will also be told that the Government must come up with more funding to save schools from "deterioration beyond redemption".
Liz Paver, the union's president, said that freeing the curriculum was more important than class size for raising standards. She said primary teachers should be given more time to teach the basics.
Mr Blunkett says his policy will be judged on meeting the Government's targets of 80 per cent of 11-year-olds reaching an appropriate standard of reading and 75 per cent an appropriate standard of numeracy by the end of Labour's first term.
Mr Blunkett has already told primary teachers they must end the years of poor literacy and numeracy. Last year, only 55 per cent of 11-year-olds reached the expected standard in maths and 57 per cent in English.
Mick Brookes, head of Sherwood junior school, Mansfield, will lead the debate on the primary curriculum. "The national curriculum is too broad," he said. "Many teachers at key stage 2 are struggling to deliver it. As a result, children are not spending enough time on the basics."
Last year, a TES survey found that three-quarters of primary heads believed they should be able to devote more time to teaching numeracy and literacy.
The NAHT says investment in the primary sector will pay dividends in the secondary, which could help to cut the pound;2.5 billion spent by authorities on special educational needs. If problems can be dealt with at an early age, less money needs to be spent on children with problems later. The union estimates it would cost pound;400 million to have an extra teacher in every primary school.
Jeff Holman, assistant secretary, said that if this was an unrealistic demand, then having an extra teacher to be shared between five schools could make a difference at the lower cost of pound;80m.
Tony Williams, head of a 850-pupilcomprehensive in the Prime Minister's Sedgefield constituency, will lead the call for more money. "Tony Blair said he had three priorities: education, education, education. We applaud that and we agreed with that, but we have three priorities: funding, funding, funding. We don't expect immediate miracles but we do expect something at the end of two years I There is a pound;3.2bn backlog of repairs."
Mr Blunkett is expected to be present for the funding debate when the conference will warn that unless the Government addresses the effect of year-on-year cuts, the situation will deterioriate beyond redemption.
School targets, page 5
NAHT centenary, page 6
Liz Paver, page 16