The complex Aegis air defense system, used by the cruiser Vincennes last week to shoot down an Iranian passenger jet, was never thoroughly tested before the Navy began deploying it, according to a classified General Accounting Office report.

The report, as described by congressional sources, found that the ability of the Aegis to discriminate among various targets was never adequately proven.The report was begun long before last Sunday's incident, in which the Vincennes shot down Iran Air Flight 655, thinking it was an Iranian F-14 fighter jet. All 290 people aboard the commercial plane were killed.

Pentagon officials are reviewing information that led the Vincennes' skipper, Capt. Will C. Rogers III, to have his ship fire missiles at the plane in the Strait of Hormuz. They have said the Aegis system aboard the Vincennes was not malfunctioning.

In an interview with the Portland Oregonian, Rep. Denny Smith, R-Ore., who was an outspoken critic of the Aegis system when it was being debated in Congress in 1983, criticized former Navy Secretary John Lehman for moving too quickly on the Aegis.

Smith said Lehman and Adm. James Watkins, former chief of naval operations, "oversold this program to themselves, to the Navy and to the public. This is a public relations coup, not a technological coup."

Smith disputed the Navy's claim that the $500 million Aegis system was built to detect and follow 200 or more targets at a time.

"If they had trouble with one airliner, what would they do with a half-dozen high-speed fighters on the deck?" he said.

He said the Navy was guilty of "a damn the torpedoes, full speed ahead, get the hulls in the water, we'll fix it later kind of attitude."

Aegis, named after the mythic shield of the Greek god Zeus, is a complex mix of radars and computers. It was developed as the main component of protection for Navy surface ships against enemy ships and planes.

The Navy is building a fleet of Aegis-class cruisers, of which the Vincennes is the third. The service is also some components of the Aegis system aboard other surface ships. The system was deployed in 1983.

The GAO review, started last year, looked at the Aegis testing program before the system went into service, said the congressional sources.