Proposals drawn up by Sir Ron Dearing, chairman of the Schools Curriculum and Assessment Authority, should carry a health warning, they said yesterday.
The news that sport will take up just 5 per cent of the curriculum has also angered some of the Government's education advisers.
The Conservative chairman of the Commons Select Committee on Education, Sir Malcolm Thornton, has written to Sir Ron to protest at the move. Launching a charter for school sport drawn up by the Central Council for Physical Recreation, with the support of the Conference of Medical Royal Colleges and all the teachers' associations, he said he shared the sports lobby's fears for the future.
'There is insufficient attention being drawn to the problems which this is going to cause for the nation, both in terms of its sporting prowess and its health,' he said.
The charter says pupils should spend at least two hours a week doing PE, but under Sir Ron's plan they would have just 80 minutes - little more than an hour once they had changed into their sports kit, according to the protesters.
Teachers should be given incentives to run sports clubs and parents should be kept informed of the progress of school teams, it adds.
The amount of sports time for each pupil per week has declined from more than two hours in 1987 to little more than one and a half in 1990, according to surveys by the Secondary Heads' Association. It fears that will now fall further.
Nine out of 10 teachers responsible for PE in primary schools had no formal qualifications, and the amount of extra-mural sport had declined, yesterday's launch heard.
Garth Crooks, the former Spurs footballer, said he was horrified by the extent to which sport had declined in the state education system. 'I daren't think back to how it would have affected my life chances if it had happened in in my time. I can't help thinking that people like myself may be affected by this reduction in PE in schools.'
Roger Uttley, a former England rugby union international and now a sports teacher at Harrow School, said Britain could not hope to improve its sporting record while school games lessons were being neglected.
'We see the England cricketers in the West Indies and it's depressing. Whenever you see England do well it's a big boost. We talk about illiteracy and the effect that has on the nation, but we are not addressing the problem of physical illiteracy,' he said.
Keith Smith, the Secondary Heads' Association sports representative and a former headmaster, said: 'Children have bodies as well as minds, and the national curriculum at the moment is affecting them. It should carry a health warning to that effect.'