There was nothing ordinary about the DC6 airplane that made an unscheduled landing recently at the Franklin Municipal Airport in Southside Virginia, 10 miles from the North Carolina border.

The four-engine plane touched down on the darkened, fog-shrouded runway at 2:30 a.m. Dec. 3, hours after the airport had closed, and its crew vanished minutes later. The plane had been stolen from a charter company on the Caribbean Island of St. Lucia. Its cargo turned out to be 22,500 pounds of marijuana with a retail value estimated at $12 million.

State police were able to confiscate the plane and its cargo -- among the largest quantities of drugs ever seized in Virginia -- because the crew fled, apparently at the approach of law enforcement officers.

Police say the incident was a dramatic example of a new phenomenon. Virginia, according to state and federal law enforcement officials, has become a major drop for smugglers who have been pushed north by stepped-up drug enforcement along the Florida coast.

"There's no question that Virginia has become an important entry point," said David Canaday, special agent in charge of the Washington office of the federal Drug Enforcement Administration. "There's so much intensified law enforcement in Florida that smugglers must find new places" to bring contraband into the U.S. from South America.

"We're not Miami, but there has been a substantial increase in incidents of smuggling and I like to think we're catching more of them," said Dennis Robertson, chief narcotics investigator for the Virginia State Police.

Virginia has several features that make the state especially attractive to smugglers: It is in the middle of the Eastern Seaboard and has rural areas where isolated farms can be rented as "safe houses" to store large caches of drugs.

But most important are the miles of remote and largely unpatrolled coastline along the Chesapeake Bay and the James, York and Rappahannock rivers. "We've got almost as much coastline and navigable waterways in Virginia as they do in Florida. It's an ideal location," said Robertson.

Boats, officials say, are more popular means of smuggling than planes, partly because they can hold larger quantities of drugs. They are also less dangerous than planes, which are often forced to land unannounced at night on dark, isolated airstrips in order to avoid detection.

In recent months law enforcement officials have seized several boats carrying large quantities of marijuana, acccording to DEA's Tidewater special agent in charge, George Notel.

Last October, officials seized a 51-foot sportfishing boat, The Crosswinds, near Pungo, Va., that was carrying 1,000 pounds of hashish hidden under large bales of rope. Notel said that seizure led officials to remote Hog Island on Virginia's Eastern Shore where another 1,000 pounds of hashish were found buried on the beach.

Last July, the Coast Guard and DEA seized a 65-foot fishing boat, The Love 2, off Virginia Beach. The boat, which attracted the attention of authorities because it was improperly rigged, was carrying 15,000 pounds of marijuana.

Although state and federal law enforcement officials say smuggling has grown dramatically in the past two years, it is impossible to determine by how much. "We estimate we're catching about 20 percent of the marijuana brought in by sea," said Coast Guard Cmdr. Robert Bastek, chief of intelligence and law enforcement for the area that includes Virginia.

In l977, the Coast Guard arrested 18 people on drug charges and seized two vessels containing five tons of marijuana and no hashish.

So far this year, the Coast Guard has arrested 30 people and seized seven vessels carrying 69 tons of marijuana and 2,062 pounds of hashish.

Those figures may increase, officials believe, because Christmas is the peak harvest season for marijuana and hashish grown in Colombia.

Last Christmas Eve, the Coast Guard seized 20 tons of marijuana from a Colombian fishing boat, "The Silvano," which ran aground in the York River. Officials arrested the captain and a seven-man Colombian crew.

The crew of the DC6 who abandoned the plane on the runway of the Franklin Airport were luckier. Robertson says state police have suspects in the case, but so far have made no arrests.

Robertson says investigators believe the pilot had flown the plane from Miami on the way to St. Lucia on Dec. 2. Somewhere along the way, investigators say they believe, the plane was diverted and flown to Colombia where the marijuana was loaded in 40-pound bags. Authorities say the entire cache was probably presold to dealers in the East and Midwest before the plane ever left Colombia.

Police say they believe the pilot intentionally flew to Franklin, where the drugs would probably have been taken to a rural "safe house." They would have been stored there for days or even weeks, awaiting the arrival of dealers using rented pickup trucks and vans to haul away quantities ranging from 500 to 5,000 pounds.

Robertson says he thinks that in the five minutes between the plane's landing and the arrival of law enforcement officials, the crew was picked up by a waiting vehicle and driven out of the area.