The Army's inventory of spare parts for aircraft, vehicles and tanks swelled from $2.7 billion worth in fiscal 2004 to $4.1 billion in fiscal 2007, mostly because the way the service projected its need for such items was flawed, according to a Government Accountability Office report released Monday.

The GAO, after scrutinizing four years' worth of Army supply inventory data, found that the Army had on average $3.6 billion in spare parts that exceeded the service's current requirements in each fiscal year from 2004 to 2007.

The Army contested the report's characterization of the parts as being in excess of its needs, saying the GAO generally classifies "current requirements" as what is required in the current year, and that the GAO figures include parts the Army intends to use.

"However, the Army plans for inventory to be either on hand or on order for the current plus the next two years thereby ensuring an adequate supply to meet the Combatant Commander's needs," an Army spokesman wrote in an e-mail.

Based on Army forecasts, the service had enough of some parts to satisfy several years, or even decades, of anticipated needs, but was short by an average of $3.5 billion on other needed parts from 2004 to 2007.

Several examples of such excesses and deficits are cited in the study.

One cites how, after anticipating an increase in the use of Black Hawk helicopters, the Army purchased 95 parts of a calibration tool used to maintain the aircraft. The anticipated uptick never came, and in fiscal 2007, the Army had 130 more of the parts than it needed, valued at $7.4 million.

At the same time, there was an unanticipated increase in operational demand for the Kiowa Warrior helicopter, "which increased the need for repairs and replacements through procurement," according to the GAO. The increase left the Army short 128 parts, valued at $1.2 million, needed to maintain the Kiowa, the report stated.

"The Army has acknowledged that challenges exist in its forecasting procedures and has begun to take steps to address shortcomings," according to the report.

In October 2008, the Army cut its forecast period in half to better account for changes in demand, and issued guidance directing managers to update their forecast models so that they match up with the actual number of parts being used.

"These two changes constitute steps toward improving the accuracy of demand forecasts, but GAO was unable to assess their effectiveness because this guidance was issued as GAO was completing its audit work," according to the report.

In December, the GAO issued a similar report criticizing Navy supply procedures, though it blamed management mistakes for the service's spending $7.5 billion a year on unneeded equipment and parts from 2004 through 2007.