The Army's $22 billion supply system is riddled with poor physical security and sloppy record-keeping, leaving some of its most sensitive weapons vulnerable to theft and other abuses, according to a new government investigation.

Investigators found inadequate storage facilities, broken detection devices and poorly equipped and trained guards at key Army installations, according to the report by the General Accounting Office, watchdog branch of Congress.

In addition to security problems, the GAO found large discrepancies in the Army's inventory system and discovered that the Army's record-keeping methods frequently masked inaccuracies.

At one facility in Germany, the GAO found surface-to-air Stinger missiles stored in lightweight corrugated metal sheds with the word "Stinger" stenciled on the side.

The report also cited an instance in which Army officials took almost a year to locate 24 Stinger missiles requested by the U.S. Army Missile Command for test firing because the Army had recorded the missiles' serial numbers inaccurately.

"The Army's known for some time that the missiles are not properly secured," said Sen. Pete Wilson (R-Calif.), who with Sen. John Glenn (D-Ohio) requested the GAO investigation.

"And yet," Wilson said, "they have failed to take corrective steps, which is unconscionable. The missiles are extremely dangerous weapons, and in the hands of terrorists would pose serious national security problems."

"We are changing our procedures to make them better," an Army spokesman said yesterday in response to the report. "That does not mean to imply there was anything inadequate about previous procedures."

The spokesman also said, "Any impression that the Army is systematically lackadaisical as an institution about its storage of missiles and weapons . . . would be an error. We weren't missing any missiles, and that wasn't an accident of luck."

The spokesman noted, however, that the Army is aware of individual cases of security problems with some weapons storage.

The GAO, which spent 11 months examining what it considered representative Army facilities, found physical security problems that included:Dragon and TOW missiles stored in tractor-trailers and on open concrete storage pads in view of people outside the protected areas. Antitank rockets stored in lightweight metal sheds with doors that had to be propped shut because the locks were broken. Antitank rockets and hand grenades stored in small, rusting metal sheds.

Army regulations require sensitive weapons such as missiles to be stored in earth-covered bunkers with steel doors and intrusion-detection systems, according to the GAO. Army officials told the GAO that money for security improvements frequently has been diverted to other programs.

Although Army officials stressed that they believe missiles and other weapons are not missing from their supply depots, the GAO said that the military's accounting system is in such disarray that the Army has no way of knowing whether much of its equipment is missing.

In fiscal year 1986, the Army's Tank Automotive Command reported inventory adjustments of $24 million, when the adjustments totaled $366 million, according to the GAO report. The difference was caused by what the GAO termed improper bookkeeping methods.

The GAO also reported that the Army's record-keeping system also hides such discrepancies. The Tank Automotive Command, for example, listed its initial accuracy rate of its records as 91 percent. The GAO found that the accuracy rate was 43 percent. Under Army regulations, the command was not required to report any individual adjustments under $800.