In an eight page memo to the Army Chief of Staff, General Peter Schoomaker, made public on Wednesday, Lieutenant-General James Helmly also complained that military leaders had rebuffed his suggestions for improvement.
"I do not wish to sound alarmist. I do wish to send a clear, distinctive signal of deepening concern," Helmly said in the memo of 20 December.
The Army Reserve is a force of 200,000 part-time soldiers who opted not to sign up for the active-duty army but can be mobilised from their civilian lives in times of national need.
Call of duty
About 52,000 Army Reserve soldiers are on active duty, with 17,000 in Iraq and 2000 in Afghanistan.
Rumsfeld is blamed by some
for the ills plaguing the Reserve
Helmly titled one section of his memo "US Army Reserve Readiness Discussion, Past Dysfunctional Practices/Policies".
The memo's purpose was to inform the Army Chief of Staff of the Reserve's "inability - under current policies, procedures and practices governing mobilisation, training and reserve component manpower management - to meet mission requirements for the wars in Iraq and Afghanistan," wrote Helmly.
His remarks gave fuel to critics of Defence Secretary Donald Rumsfeld, who argue that his policies and his resistance to a large increase in the active-duty army are harming the all-volunteer military.
Some reservists and families have also complained about frequent and lengthy tours in war zones, inferior equipment and scant notice before being pressed into service.
Helmly referred to "potential sociological damage" to the all-volunteer force by paying inducements of $1000 extra per month to reservists who volunteer to remobilise.
"We must consider the point at which we confuse volunteer to become an American soldier with mercenary," he said.