Scarab I, a robot submarine, recovered yesterday the second of the "black boxes" from the wreckage of the Air-India jetliner that disintegrated off the Irish coast June 23, killing all 329 persons on board.

The digital flight data recorder was snatched from the ocean floor by the robot arms of Scarab I about 24 hours after the cockpit voice recorder, the other black box, was recovered from the same area, 6,600 feet under water, by the same robot.

Both recorders will be flown to India for examination. There is some concern among western specialists about the equipment in India for recovering data, but India has invited international experts to assist. The National Transportation Safety Board is sending its two top specialists and Canadian and British officials also are expected to be observers.

"Reading out the digital flight data recorder is a tricky business," a source said. "If it gets screwed up, you can lose the data permanently." Investigators hope that the recorders will give evidence to prove or disprove the widely held theory that a terrorist bomb struck the plane from the sky. To date, investigators say, there is no evidence one way or the other.

However, none of the autopsies performed on the 131 bodies recovered has produced the kind of wound that is expected in an explosion, sources said. The causes of death, one source said, include "drowning and typical impact trauma." However, he said, "any of the bodies that might have been close to an explosion may not have been recovered."

Further, none of the aircraft parts retrieved from the ocean shows explosion-type damage. "But we have less than one percent of the total bulk of that airplane," the source said. "It was all secondary structure and it floated because it had honeycomb," or fiber-glass-type plastic.

The Scarab I is continuing to map the wreckage on the ocean floor. If analysis of the recorders indicates that a specific area of the plane should be inspected, attempts will be made to recover it.

The digital flight data recorder on the Air-India Boeing 747 recorded at least 16 specific pieces of information, including time, altitude, airspeed, vertical acceleration and heading. It also recorded the positions of flight controls.

The cockpit voice recorder runs continuously and contains the last 30 minutes of noise picked up by a single overhead microphone in the cockpit. Investigators study the conversations of flight crew members, radio transmissions and the sounds of switches and alarms.

The cockpit voice recorder was the key to determining what happened in the 1982 crash of an Air Florida plane into the 14th Street Bridge here. The recorded engine noises were analyzed to determine the engine speeds, and it was established that the engines were turning more slowly than the crew thought, because ice blocked sensors in the engines and caused one of the cockpit instruments to provide an inaccurate reading.

In this case, there is no guarantee that the recorders continued functioning long enough after the fatal event to provide significant clues. If a bomb is not found to be the cause of the crash, investigators are expected to turn their attention to possibilities including some unknown defect in the aircraft, a maintenance failure or a cockpit error.

Investigators are discounting for the moment the possibility that a "fifth" engine, carried under the left wing of the aircraft, could have contributed in some way to the accident. Carrying a spare engine, in a protective pod, is a common practice with the 747, Boeing officials said, and was approved by the U.S. Federal Aviation Administration when the 747 was first approved for passenger flights.