Ersatz hounds sniff contraband at airport customs

Devising ways to detect bombs, drugs, and other illegal goods at airports has led to some novel ideas. That includes everything from explosives-sniffing gerbils - they didn't get beyond the research stage - to customs agents trained to tell whether extraordinary nervousness means a traveler is concealing contraband.

But a more foolproof method may soon be in use at many airports: ''sniffing'' devices in theory as sensitive as a hound's nose.

The new generation of ''mechanical bloodhounds'' is being developed to handle some tasks for which the best conventional detectors, such as X-ray machines and keen-nosed German shepherds, are not always suited.

At Miami International Airport, US customs agents have recently begun testing a new drug-sniffer. The sensor looks like a metal detector, but is designed to pick up vapors given off by most narcotics. It works by wafting air across the travelers and then sucking it back in.

The machine chemically analyzes body smells. Within seconds, passengers are either ''cleared'' or an alarm buzzer goes off. The sensor resulted in several drug seizures during three months of testing in Houston. Lyal Hood, a customs scientist, contends the instrument is ''effective.'' But further experimentation is needed to determine its sensitivity, and to learn how prone it is to false alarms, a common problem with sniffers.

The machine is primarily seen as a better way to screen passengers. Dogs and X-ray machines are confined more to checking baggage. If successful, the sniffer is expected to be used at other airports, as well as seaports and other entry points.

A less sophisticated sniffer is being developed by US Department of Agriculture researchers for finding contraband fruits and vegetables. This one uses infrared light to measure the level of carbon dioxide in luggage. Produce emits doses of the gas.

A hand-held probe is set against the seam of a suitcase; it then siphons out air and pumps it into a portable analyzer. In theory the tool, designed at the Agricultural Research Service near Philadelphia, will pick up smells even from goods tightly wrapped.

In lab tests, the $4,000-plus instrument uncovered contraband in 24 out of 25 checks. Customs officials are now testing the probe at JFK Airport at New York. One snag: false alarms from items including old beach bags, which also produce plenty of CO2.

Illegal plants and foodstuffs are no small concern. They can be the carriers of unwelcome insects. The Mediterranean fruit fly that ravaged California crops in 1981 was believed to have been brought in on contraband produce. In 1981, the most recent year for which there are statistics, customs agents seized some 700, 000 illegal articles at US airports. Agents now rely on hand inspections and, in some cases, X-ray machines to spot them.

In Canada, researchers are working on a new sniffer to detect explosives. The sensor is to be used to uncover bombs in the plane rather than to screen passengers as they board. The briefcase-size detector samples the cabin air and, through gas chromatography, detects the presence of vapors given off by most explosives.

Researchers at the Canadian National Research Council, where the instrument was invented, claim it is at least 10 times as effective as ones now available.

''It will result in far fewer false alarms than dogs might have,'' claims Dr. Harold Seigel, president of Scintrex Ltd., a Toronto-based instrument and research firm. Scintrex, which will manufacture the machines, plans to put the first ones on the market by year's end, at about $12,000 apiece.

But some outside observers remain dubious. They question how many different types of explosives the instrument will track down. Still, any improvement in detection would be welcomed.

Mechanical explosives sensors do exist now. They are used chiefly by police, power-plant operators, governments, and some industrial companies. But most of these are ''very good dynamite detectors and nothing else,'' says Dr. John Hobbs , a chemist and explosives expert with the Transportation Systems Center, an arm of the US Department of Transportation.