The Army is so short of spare parts for its helicopter fleet that it is spending tens of millions of dollars to overhaul old parts, the General Accounting Office has reported.

"The increase in part shortages has resulted in unnecessary cost to the taxpayer and unnecesary risk in the event of combat," said Sen. William V. Roth Jr. (R-Del.), who requested the study by the congressional watchdog agency.

The study focused on the Army Depot in Corpus Christi, Tex., largest of the eight depots where the service repairs about 20 percent of its 8,400 helicopters.

The study notes that the average helicopter has 13,000 different parts, any of which might need replacing during an overhaul.

When correct replacements are unavailable, the depot teams worked around the shortages, which added extra work and cost, the GAO found. The most common form of working around a shortage was to repair a worn part, rather than to throw it away.

For example, the study said, the average cost of a new tailboom fitting for a UH1 Huey was $352, while a repaired fitting was $1,005. The GAO found that, during its review, the depot had repaired 72 of the fittings, adding what it said was $47,000 to overhaul costs of the 72 helicopters.

When the parts are unavailable and repairs cannot be made, the helicopters are grounded.

"The bottom line is that when parts aren't repairable or available, the Army is forced to ground hundreds of helicopters," Roth said. "If caught at an inopportune time, this could be crippling to our combat readiness."

The Army, in a response that was part of the GAO report, said it is aware of the problems and is trying to correct them. Robert Costello, assistant secretary of defense for production and logistics, said "action had already been taken to address many of" the problems.