Tory MPs said they will be holding their fire, until they are told the details, but they were alarmed at reports that 10,000 back-up troops could be cut with 15,000 civilians.
'I support many of the things they are looking at, but if they proposed cutting 10,000 uniformed troops, I could not vote for the Government,' one former defence minister said.
The defence White Paper will outline the impact of the Options for Change - brought in after the Cold War ended - but will offer no details on the fresh package of cuts in defence support services, called 'front line first', to be presented later this week to ministers.
Malcolm Rifkind, Secretary of State for Defence, said yesterday the review would not weaken the front- line capability of the armed services. He told BBC Radio 4's Today programme: 'It is quite possible that some jobs will go . . . but they will not be front-line jobs.
'They will not be the people who actually have to do the fighting. It will only be (done) if we can be satisfied that the quality of work can be done in a way that involves the use of less manpower.'
The wide-ranging plans include the closure of many defence bases, the leasing of heavy equipment and entire fleets of vehicles, the merging of defence colleges, slashing ranks in the armed services and the closure of recruitment centres.
Some Tory MPs would oppose the closure of firing ranges and TA centres in towns. The flashpoint with the opposition parties could come over the threatened closure of the Rosyth naval base. Mr Rifkind said there were no plans to close the dockyard, but he confirmed the naval base was under review.
The Rosyth naval base campaign group last night warned it would fight the closure, which could cost 15,000 jobs. Menzies Campbell, the Liberal Democrat spokesman on defence, said: 'The 'front line first' review has undermined the defence White Paper.'
He called for the Ministry of Defence to make alternative savings by withdrawing from Germany to Britain the entire force of 78 RAF Tornado ground attack aircraft and 40 Harrier jump jets. He said their role, to attack Warsaw pact forces in Europe, had gone with the end of the Cold War.