In a little-noticed building on Constitution Avenue, a dedicated band of experts is engaged in a new-ending game of hide-and-seek. They are the special analysts of the U.S. Customs Service who are charged with keeping up with the multifarious ways that narcotics rings smuggle their products into the American bloodstream.

They receive a daily flow of reports from customs and narcotics agents on seizures of cocaine, marijuana, hashish and heroin throughout the country. In turn, they compile the latest data on new smuggling techniques and send out confidential intelligence communiques to agents in the field.

It is a constant game of wits between the traffickers and the lawmen. The latter never cease to be astonished by the devices used by the drug rings to sneak their wares into the United States. Some of the methods were virtually impossible to detect until the customs experts came up with new scientific detectors.

Here, culled from confidential intelligence reports and enforcement bulletins, are examples of what they have had to cope with:

Cocaine in its base form can literally be made to disappear. This chemical legerdemain, according to one intelligence report, is accomplished by mixing or concealing the cocaine base "in a product which has the appearance of being legitimately importable. "It can be mixed with motor oil, gasoline, liquor or windshield-wiper solution. It can be dissolved "in the water of a sewage-holding tank of a camper" or "mixed with clay or plaster of paris and formed into such items as statues and pots."

Occasionally, customs inspectors manage to detect the invisible cocaine. Last year, acourier from Ecuador was found to be carrying "nearly two kilos of cocaine base molded into pottery." A California group was discovered smuggling cocaine base from Bolivia in liquor bottles.

One imaginative gang of traffickers stashed their cocaine inside long-playing phonograph records. They "split" the records in half, placed thin plastic bags full of cocaine between the halves, then resealed the records with glue. The smugglers were caught by their own greed: the weight of one of the albums tipped off narcotics officers. But they had already managed to bring in at least 36 shipments of cocaine.

Two months ago, a customs officer at Houston International Airport opened a package from Ecuador and found several boxes of tea, chocolate and cans of peaches from Chile. The cans appeared to be factory-sealed, but they felt light. The can tops, moreover, could be depressed and popped back into place. Closer inspection turned up 2,300 grams of cocaine.

Narcotics police in Montreal last year seized a hollowed-out Eisenhower silver dollar from known drug users. In Virginia Beach, Va., a store clerk dropped a Kennedy 50-cent piece and saw it split in half. Both coins, say intelligence reports, could be used to "conceal a small amount of powder, such as heroin or cocaine."

Customs inspectors recently discovered a cattle truck with a false bottom under the floor. "The truck contained cattle," which had "to be unloaded to retrieve the marijuana stored in the compartment," recounts a classified document.

These examples offer but a brief glimpse into the smugglers' bag of tricks. In 1977 alone, nevertheless, the Customs Service managed to seize 24,288 lots of narcotics and dangerous drugs, worth a total of $930,661,485. As impressive as these figures appear, some experts estimate that they represent as little as 10 percent of the drugs smuggled into the United States.

Even better detection, customs experts believe, can be achieved through the use of advanced technology. "Projects and tests already under way," states one internal report, "indicate that we will rely even more heavily in the future on devices and systems, some straight from a "Star Wars" scenario, to improve the effectiveness, efficiency and safety of our operations."

One project under development is a "vapor detection system" that can spot heroin, cocaine, marijuana and hashish in parcels, luggage and clothing. The device works by picking up the chemical vapors exuded by narcotics. Another futuristic tool now being refined is the "neutron backscatter" which directs neutron beams at an object and analyzes the returning neutrons. With the backscatter, says the report, the "presence of narcotics can be detected readily." It is "hand-held, fully portable and operated by one person."

Various X-ray devices are still being fine-tuned by researchers, as is a technique called "dielectric discontinuity." This process "permits the rapid inspection of large volumes of foreign letter mail by measuring the electrical characteristics of the letter and comparing them with the 'signatures' of narcotics and explosives."

Researchers are also working on several "night vision" instruments. They have developed a set of goggles, for example, that "enable Customs field officers to see in virtual darkness, while their hands are free to drive vehicles, hold radios and carry firearms." In a recent Oregon case, customs officers seized over $3.7 million worth of cocaine because they were able to watch a nighttime rendezvous from a distant railroad caboose.