Moves to build 1,000 homes on Green Belt land near the Kassam Stadium will be bitterly fought by South Oxfordshire District Council.
The council says it is outraged at a proposal to "dump" a major housing development in its district, after the idea won backing from Oxfordshire County Council.
It will be joined in opposing the new homes by Oxford Preservation Trust, which today pledged to save Oxford's Green Belt.
County councillors on Tuesday confirmed their support for the homes on land south of Grenoble Road, agreeing to amend the Structure Plan, which will control development in Oxfordshire until 2016.
Conservative county councillor Charles Shouler successfully urged County Hall to back the urban extension of Oxford beyond the ring road, to spare Bicester from unwanted development.
His initiative was welcomed by both Oxford City Council, as a way of combating the city's housing shortage, and Magdalen College, which owns most of the land.
But the idea of developing a site stretching from Greater Leys to the Oxford Science Park has already run into trouble.
District council leader Ann Ducker said: "It flies in the face of national planning policies designed to protect the Green Belt.
"The people living in the rural towns and villages of south Oxfordshire need their council to stand up and fight on their behalf."
Head of city council planning, Adrian Duffield, said: "What has been proposed needs careful examination."
Debbie Dance, secretary of Oxford Preservation Trust, said the county council's vote came as a complete shock.
"The trust is appalled at the idea," she said.
"If it is included in the document that goes out for consultation, we will fight it and we will win."
The senior bursar of Magdalen College, Charles Young, said the development would provide the college with a welcome opportunity to expand Oxford Science Park.
He said: "Broadly speaking we support the idea."
There was support too in Bicester, which hopes the Grenoble Road proposal will avoid hundreds more homes being built in the town between 2011 and 2016.
A draft version of the plan will now go out to public consultation in September for six weeks.
Mr Shouler said: "It could be that eventually, after consultations, the 1,000 homes will be imposed on Bicester by the Deputy Prime Minister John Prescott through the regional planning organisation based in Guildford."
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