MIAMI (AP) _ A $1 million, state-of-the-art bomb detector is sitting in a crate at the Miami airport while Pam American World Airways argues with the manufacturer over liability insurance.

The airline is worried that the thermal neutron analysis device - only the second of its kind - could leak radiation, spawning costly lawsuits, and wants the manufacturer to shoulder the insurance payments.

The machine can detect plastic explosives in checked baggage. Current X-ray equipment is incapable of sensing bombs like the one believed to have downed a Pan Am jumbo jet over Lockerbie, Scotand in December 1988, killing 270 people.

The FAA bought the new device and delivered it in August to Miami International Airport for Pan Am's use. The agency has mandated installation of the machines in 40 high-risk airports around the world.

Trans World Airlines made no complaint when the first machine was installed at its terminal at New York's John F. Kennedy Airport in September, said Monte Begler, associate administrator of the Federal Aviation Administration.

Pan Am's reaction was unexpected, he said, and ''I'd be less than candid if I didn't say I was disappointed.''

Officials at New York-based Pam Am say they fear that passengers could claim harm from the gamma rays emitted by the machine.

''We need to protect Pan Am. The likelihood of being sued is very high,'' Pan Am spokeswoman Pamela Hanlon said.

The manufacturer says the airline's concerns are groundless.

''There is no risk,'' said Hadi Bozorgmanesh, vice president of Science Applications International Corp. of San Diego. ''If there were, we wouldn't have gotten a license from the Nuclear Regulatory Commission.''

Families of victims of the Scotland crash are angered by what they see as Pan Am's foot-dragging, said Victoria Cummings of Coral Gables, whose husband died in the bombing.

''It's appalling that this kind of thing can get caught up in politics and profits,'' Mrs. Cummings said. ''The industry has only its bottom-line profit in mind ... It will probably take more people getting blown out of the sky to get the priorities changed.''

Airline officials also have questioned whether the expensive equipment works.

During an August speech in Miami, Pan Am Senior Vice President Robert Gould charged that the government was forcing airlines - which must pay for all but the first six machines - to buy them for political reasons.

''Mandating (new technology) may please a constituency, but it doesn't enhance safety,'' Gould said. ''I don't believe it is as effective as the public may think it is, and, therefore, we're going to give a false impression about security.''