Pentagon investigators will be taking a close look at whether the USS Vincennes detected radar signals emanating from the Iran A300 Airbus that it mistook for an F-14 fighter and shot down, military and industry sources say.

Publicly available evidence suggests that the Airbus was not using its weather or navigational radar, which send out different signals than radar aboard an F-14 and could easily have been distinguished by equipment aboard the Vincennes, according to Pentagon officials."If an F-14 is using its target acquisition radar, it is a very specific signal, and one which you can easily identify," Pentagon spokesman Dan Howard told reporters on July 5, two days after the incident.

Pentagon and industry sources said it would be common practice for either an attacking F-14 or an Airbus making the 175-mile run in clear weather between Bandar Abbas, Iran, and Dubai, in the United Arab Emirates, not to turn on its radar.

"The Iranians know when they paint something with their target illumination radar, that we can detect it and we can identify the target very specifically from that information," Howard said.

"It's not necessary to turn a lot of this equipment on if you know the location already from other sources," he said. "You can wait until you actually release your ordnance."

The absence of a radar signal, therefore, would tell the Vincennes' officers nothing about the approaching plane, but any radar signal originating from the Iranian aircraft should have identified it as civilian or military.

A computer analysis of electronic data from the Vincennes has been conducted in the United States and flown to Bahrain, in the Persian Gulf, where a six-member team headed by Rear Adm. William M. Fogarty is investigating the incident. Pentagon officials have declined to discuss information uncovered by Fogarty, including whether the Iranian aircraft was sending out radar signals.

A device known as a transponder aboard the Airbus was sending one set of identification signals common to civilian and military aircraft, as well as a signal unique to warplanes, Howard said.

And the chairman of the Joint Chiefs of Staff, Adm. William J. Crowe Jr., said that it was impossible for a ship to use its own radar to precisely identify an approaching aircraft, a view shared by Navy and industry officials who spoke on condition of anonymity.

The issue of whether the Airbus was emitting radar signals is quite different, however, and the answer is not likely to be known publicly until the results of the Fogarty investigation are released, something that Navy officials now say they do not expect until mid-August.

The Vincennes, and many other U.S. warships in the gulf, are equipped with a device known as a SLQ-32, which can distinguish the "signatures" of radars. Radars that are used by commercial airliners are quite different from those used by military aircraft.

The exact differences are classified, industry and Navy sources said, but generally military radars are far more powerful, operate on different frequencies, radiate farther, and "ping" objects more frequently with radio waves than do commercial radars, they said.

The SLQ-32, manufactured by Raytheon, Corp. of Massachusetts "is a little like a fuzz-buster," said one industry source. "It can spot a highway cop if he has his radar on. But if he doesn't have his radar on, you won't spot him."