The commitment comes despite a recent Audit Commission report, entitled Trading Places, which warned that the current system was already fraught with problems, with many parents failing to get the school of their choice for their children.
In Bromley, hundreds of parents discovered their children had not been offered a place for this September because 800 of the 3,000 places available had been given to pupils living outside the borough.
The proposal would make the local education authority a clearing house for pupils without places. The LEA would still have a strategic role in admissions and would be responsible for closing down schools where rolls were falling.
In the present system, grant- maintained schools and voluntary-aided schools determine their own admissions. And it is the Conservatives' plan for all LEA schools to be based upon the voluntary-aided model.
Margaret Smart, the director of the Catholic Education Service, said: "Our voluntary-aided schools always work closely with the LEA in the planning of admission and the criteria for admissions."
Walter Ulrich, a spokesman for the National Association of Governors and Managers, said: "To allow every governing body to control admissions, even in consultation with the LEA, raises the question of practicability when the matters of choice and duty to educate a child come into conflict. The experience of areas which have mixed admission policies has not been encouraging."
But a Conservative source dismissed the fears that an admissions free for all would cause chaos, saying parents must accept that greater freedoms often require greater responsibility.
In its manifesto published last week, Labour made no mention of any admissions policy, except to say that any changes in admissions to grammar schools would have to be decided by local parents.
Previous policy statements have indicated that Labour would not seek to reverse the Conservatives' open admissions policy.