Israel's spectacular success in knocking out Syrian batteries of Soviet-made surface-to-air missiles during last week's invasion of Lebanon was the result of a technological breakthrough involving the use of pilotless aircraft and electronic countermeasures that rendered the defense system ineffective, according to Lebanese military intelligence sources.

The raid, which Syria said involved more than 90 Israeli jets, must have caused Syrian and Soviet military planners deep concern about the future usefulness of the SA6 missiles, which were deployed in Lebanon's Bekaa Valley.

In the 1973 Middle East war, Egypt and Syria used the SA6 missiles with considerable success against the Israeli Air Force to provide a protective air screen for Arab forces.

Such an air screen was rendered ineffective in last week's fighting.

In their air raid Wednesday, the Israelis said they knocked out all the missile batteries in the valley and shot down 29 Syrian Migs in the operation with no losses of their own. Syria claimed to have downed 19 Israeli jets and immediately replaced some of the destroyed missiles in what they called "the biggest air battle in Middle East history."

Lebanese intelligence sources provided some details of the Israeli technique used to strike at the missile batteries while keeping the missiles from hitting the attacking jets.

They said the Israelis sent over drones--small pilotless jets--in advance of the warplanes to act as decoys. The SA6, which is mounted on a modified tank and has a range of about 22 miles, has sophisticated radar guidance and homing systems using a combination of radio frequencies, according to the weapons handbook, Jane's.

When the Syrians shot down the drones with the missiles, the Israelis were able to determine the radio wavelength the missiles were operating on, the sources said.

Two waves of Israeli jets later swept down on the missile batteries, and took unspecified countermeasures based on the detected radio frequencies to render the missiles ineffective, according to the sources.

The countermeasures enabled the Israeli planes to "confuse" the guidance system of the Syrian missiles, which went awry once they were launched against the jets, the sources said.

It was not clear how Lebanese intelligence had arrived at these observations about the Israeli technique. The drones, however, have been in use over Lebanon for some time, and both Lebanese and other intelligence agencies have been able to study their capabilities.

The sources did not say how many drones were used or when precisely they were sent over the missiles to draw their fire prior to the Israeli attack.

Reporters saw a number of such drones flying over the Bekaa Valley in the days before the raid. It may be that some, or all of the 19 Israeli jets Syria claims to have shot down in the raid were actually drones.

Those used in the operation were not identified, but the most common pilotless surveillance aircraft the Israeli Air Force uses is an Israeli-produced version of the American Firebee. There appears to be nothing new in this tactic of using the radio-controlled drones, which have built-in cameras, as missile bait.

Last summer, during Israeli attacks on Palestinian positions in southern Lebanon, Syria reported shooting down at least a half-dozen drones. Israel had threatened then to attack the missile batteries, which were brought into the Bekaa Valley in April 1981 after Israeli jets shot down two Syrian helicopters.

The Lebanese military sources also said they believed the Israelis used American-made E2C Hawkeye reconnaissance planes, a simpler version of the Airborne Warning and Control System (AWACS), to coordinate the whole attack on the Syrian missile batteries.

The Hawkeyes flew high above the Bekaa Valley, the sources said. But other analysts here were not sure that the Hawkeye could be employed safely in that manner.

One Lebanese intelligence source, reflecting on the Israeli use of such advanced devices as cluster and fragmentation bombs and probable use of laser-guided "smart bombs," remarked, "Technology is the winner in this war."

But he also blamed the same American-supplied advanced weapons now in the hands of the Israelis for the high civilian toll.

"The very nature of the weapons used will cause heavy damage among civilians," he said, noting the example of one 2,000-pound bomb that missed its target--a Syrian artillery position in the mountains just east of Beirut--and made a huge crater in a residential neighborhood.