A bomb believed to have been concealed in stereo equipment that was seized from Palestinian extremists exploded Monday at West German police headquarters, seriously injuring two explosives experts, authorities said.

The experts were checking a hi-fi tuner impounded during a raid on an "extremist Palestinian terrorist group" when the device exploded, police spokeswoman Brunnhilde Spies-Mohr said.The explosion took place "around lunchtime" and "demolished" the room in which the device was being checked at the criminal police headquarters in Wiesbaden, near Frankfurt, the spokeswoman said.

The two policemen, ages 30 and 35, were injured, she said. "We don't know much at the moment; investigations have just started. Our main worry at this stage is for the life of our colleagues," she said.

The spokeswoman, contacted by telephone from Bonn, said it was too early to determine whether the device was similar to a radio-cassette bomb that blew up Pan American World Airways Flight 103 over Lockerbie, Scotland, Dec. 21.

Some 270 people were killed when the plane exploded on a flight from Frankfurt to New York. Authorities said the Damascus-based Popular Front for the Liberation of Palestine-General Command, or PFLP-GC, was a suspect.

The police spokeswoman declined to confirm speculation that the current police crackdown on Palestinian extremists was against suspected members of the PFLP-GC.

In November, West German police found two radio-cassette bombs at Palestinian extremist hideouts and questioned 13 suspects.