A few days before Thanksgiving, two Calvert County sheriff's deputies escorted a locked rental truck from the shores of the Chesapeake Bay across county and state lines to Washington National Airport where the cargo was to be shipped to California.

The airport was where the trouble began. First, airport security police were called in and began the airline refused to load the cargo. Then the to ask tough questions. Finally, a call was placed to the U.S. Attorney's Office in Alexandria, making a federal case out of the whole affair.

The problem was that the cargo consisted of 17 slot machines. And for some years, it has been a federal crime to transport slot machines across state lines.

"It was," said Calvert County Sheriff Adrian Joy yesterday, "a helluva mess."

After much questioning, it was determined that the deputies were escorting the shipment merely to make sure that the slot machines did not fall into the wrong hands before they were shipped to California. So a compromise was reached: if the deputies escorted the machines back into Maryland (and found some other - legal route whereby to ship the machine) the federal government would forget the whole affair.

Everyone's intentions were honorable, said a U.S. attorney yesterday, "so we took no action."

Slot machines, once an economic mainstay in Calvert County along with tobacco and other cash crops, have been outlawed in Maryland since 1968. Untold numbers of aging machines - still owned by their original owners - remain rusting in padlocked warehouses and storage rooms throughout the tiny, rural county, however, Sheriff Joy is responsible for making sure that all of them are accounted for and unused.

"Everyone though they were coming back and that their stores was just a temporary tghing," said State's Attorney Naji P. Maloof yesterday. But it was not temporary. And now, with the state itself in the gambling business with its daily lottery, the odds on the return of the privately owned slots, which would compete with the revenue-raising numbers games, is generally considered infinitesimal.

The slot owners, therefore found themselves caught in a legal conumdurm:

Since it is illegal in Maryland to "possess" slot machines, how could they sell what they could not process? As a buyer from another state where possession, if not the use of slots is legal could you take "possession" in Maryland?

The law remains unclear on that point, according to several legal observers, but the Calvert County Commissioners, without objection from the state, agreed not to prosecute that sellers or buyers if they went through official channels.

Dave Ritchie, owner of the 17 slot machines that caused problems at National Airport, was one such seller. He had his 17 1939-vintage machines stored at his Breezy Point Beach marina and had found a California collector willing to pay $300 for each of them.

According to Maloof, under a recently enacted law in California, pre-1941 slot machines can be privately owned as a "collectibles."

The problems at National, however, did not daunt the collector, who drove the truck that carried the slot machines to the airport - followed by the two deputies in a county car.

He promptly took them to Baltimore-Washington Airport for shipment. But not to California. Instead, it was decided to ship them to Las Vegas, a known safe haven for errant slot machines, while the legal problems of interstate transportation to California could be worked out.

"I'm happy to get rid of them because all they cause is trouble," said Maloof yesterday of slot machines in general. He said he plans to call California next week to learn in whose hands the machines eventually ended.