Mr Major promised to protect school pitches as part of his recent sports initiative. But in a separate bid to encourage opt outs he has told grant-maintained schools that they can now keep all profits from the sale of their assets.
Playing fields campaigners say the announcement may induce governors to sell off land for development.
Mrs Elsa Davies, director of the National Playing Fields Association (NPFA), said: "We are very concerned about this because there is a clear contradiction in the message to schools."
At the same time, local authorities say they are still being forced to sell off recreational land because of government cash restraints and pressure to reduce surplus school places.
The NPFA hears of five new threats to recreational land each week but it says more land, not less, will soon be needed. The school population will rise by 17 per cent in the decade leading up to the year 2000. Mrs Davies fears that schools will sell off surplus land only to find that when they need it again it is no longer available.
In the past, opted-out schools have received as little as half the proceeds from the sale of assets, with the rest going to the local authority. This autumn the government will legislate to allow them to keep all the money.
Downing Street insists that the change will not harm sports facilities. "There is no contradiction here. The safeguards which the Prime Minister has flagged will remain," a spokesman said.
But sports lobbying groups say there are other flaws in Mr Major's sports plans. Much tougher action is needed to stop the loss of playing fields and recreational land and to promote links between schools and sports clubs, they argue.
Keith Smith, deputy chairman of the Central Council for Physical Recreation, met Downing Street policy advisers last week. He said that while he was reassured that Mr Major did not intend to give schools an incentive to sell sports pitches, the council was still concerned about other issues.
The government's minimum requirements for playing field space per pupil were too low, he said, and many schools already had less than that.
The committee says several million pounds of lottery money must be put into sports clubs so that they can pay schools for the use of shared facilities.
"If there is some quid pro quo for this exchange of facilities the net result could well be that schools will make different decisions about selling off playing fields," Mr Smith said.
Meanwhile, local authorities say government policies are forcing them to sell off recreational land. North Tyneside says it must sell seven pieces of education land in order to carry out some of the pounds 5 million of repairs needed for schools. This year its capital grants for education amounted to just pounds 78,000.Reuse content