The Government has been advised by the Defence Forces that any attempt to reduce their strength could "destroy cohesion, morale and military effectiveness" at a time when the State is taking an increased role in peacekeeping missions.
The warning comes in a submission from the Defence Forces' Chiefs-of-Staff on the White Paper on Defence, which is due for publication in the coming weeks. The Defence Forces' submission was made late last year.
There are growing military concerns, primed by leaks from a Department of Defence submission to the White Paper, that the Government intends to reduce the size of the Defence Forces from 11,500 to 10,800 or less.
There have also been indications that the Government has considered reducing the Army from a three-brigade structure to a one-brigade one.
This week, the Defence Forces' Chief-of-Staff, Lieut Gen Dave Stapleton, indicated to his senior staff officers that the submission reflected his views on the future of the Defence Forces, particularly that it should not be further reduced in size or structure.
It is understood the Chief-of-Staff feels strongly that if there is any further reduction in the size or structure of the Army, it will not be able to fulfil either its domestic defence role or its increasing foreign peacekeeping role.
The recent Government decision to join the NATO-led Partnership for Peace (PfP) organisation has been accompanied by an increased Defence Forces' participation in foreign missions. In the past six months military contingents have been sent to Kosovo and East Timor.
The military submission to the White Paper pointed out that the Defence Forces have already been subjected to repeated reviews and examination by consultants. This resulted in the Army's reduction from a five-brigade to three-brigade structure, and from a strength of 13,000 to 11,500.
The submission says the three-brigade structure "is designed as the minimum necessary to meet the nation's defence and security requirements in the uncertain and changing years ahead".
It adds: "Unless there is a dramatic improvement in the national, regional and international security situation, the strength of the permanent Defence Forces must not be permitted to fall below the authorised strength of 11,500.
"The force structure anticipates continued progress and improvement in the defence and security environment and the evolving European security architecture.
"The new force structure forms the basis on which contingency plans can be prepared. It improves operational and training capacity and facilitates commitments to peace-support operations.
"The restructuring also assumes that future commitments of the Defence Forces will often be in partnership with other nations and must take account of the organisation's obligations to the overall objectives of such missions. Any additional reduction of the 11,500 would seriously risk the danger of destroying the cohesion, morale and military effectiveness of today's Defence Forces."
It adds that this damage would come at a time when there is a "continuum" of regional conflicts and when the State has increased its commitment to peacekeeping missions through its participation in PfP, the UN, and other organisations such as the Organisation for Security and Co-operation in Europe.
At present there are 800 Irish military personnel serving with one or other of those organisations on peacekeeping missions.
The Defence Forces' submission says the Republic's membership of PfP will increase its commitment to foreign peacekeeping missions, and that the PfP can benefit from the Army's 41 years of experience of peacekeeping with the UN.