Gordon Brown, the shadow Chancellor and local Labour MP, leading the campaigners to save the base, said they would use a 90- day consultation period in an attempt to reverse the run-down.
The decision will be confirmed today by Malcolm Rifkind, the Secretary of State for Defence, as part of defence cuts of pounds 750m a year over three years. He will sweeten the pill by announcing large-scale equipment orders.
Mr Rifkind has won a battle with the Treasury to avoid the pounds 500m redundancy package being paid out of the cuts in support services, codenamed Front Line First. He will reassure Tory MPs that substantial savings will be used to sharpen the 'teeth' at the expense of the military tail.
But senior Tory Party sources fear a backlash in the Tory heartlands. One source said the Rosyth decision had acted as a smokescreen for the closure of dozens of small bases across the South of England, which could lead to an outcry by Tory MPs in marginal seats. About 8,000 civilian and 12,000 service jobs will go.
Ministers are braced for protests, but estimate that no more than 800 jobs will be lost in any single constituency. Some Tory MPs were also ready to protest over cuts in the armed forces medical corps and plans to reduce the number of military hospitals from three to one, with the NHS providing more cover.
Minesweepers and fishery protection vessels will be transferred to other bases. However, it will be kept on a care and maintenance basis to allow it to be reopened in a crisis, enabling some of the 1,300 jobs to be saved.
Defence sources said a mixed civilian and naval team will remain - which was always the plan. Situated next to the dockyard, which is commercially managed, there will be a need for some military presence to oversee and accept warships refitted there.
The announcement is the most significant political and economic development north of the border since the closure of the Ravenscraig steel works in 1992. Senior Conservatives fear that it will have severe electoral consequences, putting at risk most of their 11 Scottish seats.Reuse content