Armed forces face first review in a decade.
Defence Secretary Bob Ainsworth will publish an interim green paper on the issues to be covered early next year, with a view to holding a full strategic defence review early in the next parliament.
The Tories, who could be in power by that time, indicated that a Conservative government could use the green paper to inform its thinking when it carried out its own promised SDR.
Mr Ainsworth said the review was designed to ensure "we develop and maintain armed forces appropriate to the challenges we face and the aims we set ourselves as a nation".
The issues to be considered in the green paper will include the changing strategic context, the lessons from recent operations, the exercise of "soft power" to prevent future conflicts, and the impact of technological changes.
It will also look at ways of improving processes for procuring equipment and the modern day requirements on and aspirations of armed forces personnel.