Japanese officials announced yesterday that breakage and signs of possible metal fatigue have been found around an improperly repaired section of the Japan Air Lines jumbo jet that crashed Aug. 12, killing 520 persons aboard.

Officials declined to draw conclusions from their finding. But it is expected to affect the final judgment on whether the accident was caused by faulty repairs that the Boeing Co. has acknowledged it conducted on the jet, Washington Post correspondent John Burgess reported.

The accident is widely believed to have begun with the collapse of the Boeing 747's rear pressure bulkhead, a metal structure that sealed the end of the jet's fuselage. This is thought to have released pressurized air from the cabin with explosive force, tearing away major parts of the plane's tail section and causing the crew to lose control.

In 1978, following an accident in which the jet banged its tail hard during a landing, Boeing made extensive repairs to its tail section, including the bulkhead. Boeing says it has not been shown whether improper repairs had played a role in the accident.

The new findings add fuel to theories that the bad repairs caused the bulkhead to break. Such a finding could raise Boeing's liability in paying compensation to the victims' families but also would demonstrate that there is no basic design flaw in other 747s.