THE US Army has only three spare brigades - fewer than 15,000 men - available to deal with unexpected crises such as North Korea because of the drain on manpower in Iraq, Afghanistan, and the Balkans.

It has the equivalent of twice that number serving food, staffing pharmacies, and stacking shelves in depots world-wide.

The Pentagon is now considering a scheme to hire civilian contractors to carry out rear-area administrative tasks to free up trained soldiers for combat and peacekeeping missions and has identified more than 320,000 jobs currently occupied by uniformed personnel from all three armed services.

Planners say it would be cheaper and more efficient to recruit civilians to run food, stores, and some medical facilities and would allow the army, navy, and air force to get their money's worth from expensively-trained service personnel.

The prime example held up for comparison is the US Marine Corps, where every member - whether cook, pilot, chaplain, or tank commander - is a rifleman first and a specialist second and must maintain combat readiness to fight at that basic level if called upon.

The Pentagon is also drawing up plans to activate two of its best-trained national guard brigades for 15-month tours of duty to relieve the pressure on the regular army as peacekeepers in Iraq in response to the unforeseen need to maintain an army of occupation of almost 150,000.

The original US blueprint for war called for a rapid victory and the reduction of troop levels to 50,000 within a few months.

Unexpected resistance and the reluctance of allies to commit men to an open-ended and dangerous deployment without a UN security council mandate has intensified the drain on resources.

There are currently 370,000 men and women deployed in 120 countries from an active duty US Army of 491,000.

A total of 136,000 part-time national guard volunteers and ex-regular reserves have also been called up, the biggest mobilisation since Vietnam.

The problem is that combat troops - the infantry, tank crews, artillerymen and engineers - are in limited supply. And while recent wars in Afghanistan and Iraq have been won using a combination of high-tech weaponry and relatively few soldiers, holding territory needs ''boots on the ground'' in large numbers.

Pending the results of a Pentagon study into the widening gulf between global commitments and available manpower, Donald Rumsfeld, the US defence secretary, may now have to seek funding for an increase in the numbers of soldiers in traditional brigades and divisions at the expense of technological wonder-weapons.