Small airplanes, those wonderful machines that give weekend thrills to would-be fighter pilots, carry politicians to remote hamlets for lunch with the Elks, and ferry businessmen to out-of-the-way investments, have taken on a new role: smuggling marijuana.

Between 10,200 and 13,700 tons of marijuana worth up to $13.7 billion were smuggled into the United States in 1979, and about a third of the total came by air, the Drug Enforcement Administration estimates.

Enforcement is like trying to swat flies in a barn. Only 170 tons were recovered in various arrests and seizures from small planes, as well as 11 tons of Quaaludes and 1,586 pounds of herion. Many more flights get through than are ever caught or even detected, federal officials agree.

"You can't pass a regulation that will [automatically] correct illegal activity," said Richard Lally, chief of civil aviation security for the Federal Aviation Administration.

Planes are in such demand that small-plane thefts have increased markedly in a few years. A total of 241 small, privately owned aircraft worth of $20.7 million were stolen last year, 110 of them from Florida and Calfornia, and 39 from Texas and Arizona, according to the International Aviation Theft Bureau. As recently as 1978 only 76 thefts were reported. About 210,000 small planes are registered in the United States.

The problem has caught aircraft owners and manufacturers unprepared for private planes are easy to steal for those who know how, and it has given the Federal Aviation Administration a new headache: pilots flying drugs in stolen airplanes take shortcuts that cost them their lives.

In 1980 alone, there were 207 crashes of small planes that apparently were involved in drug-smuggling activities, according to FAA records. Many of the planes were reported stolen. Others had registration numbers that checked back to phony owners, still others were just borrowed or rented, apparently for legal purposes, then used for something else indeed.

Some examples:

Sometime between 10 p.m. and midnight last Oct. 30, pilot Richard Lee Rohrman's twin-engine Cessna 404 spun out of the sky and dropped like a rock into the Florida swamp 20 miles north of Tampa. Rohrman was killed instantly and the Pasco County sheriff's office recovered 2,300 pounds of marijuana and $22,000 in cash.

On Oct. 1, 1979, a Cessna Titan flying low near Boca Raton, Fla., flew into a 175-foot radio tower, knocked off the top 30 feet, and flew another 50 miles before being ditched in the Everglades. The copilot was killed, apparently when the plane hit the tower. Investigators think the pilot walked away, and he has never been positively identified. The plane had a load of marijuana and papers indicating it came from Kingston, Jamaica.

On March 2, an Aero Grand Commander crashed two miles south of La Belle, Fla., and two people were killed. Drugs were found on board. The plane was registered to an owner in California.

On March 13, a Piper Aztec stolen the night before from an airport near Charlotte, N.C., crashed at 2 a.m. near Kingstree, S.C., killing both men on board. "We think the plane had already landed and had unloaded and had just taken off," said Theodore McFarlin, sheriff of Williamsburg County. The Kingstree airport has no tower and one short asphalt runway about 50 miles from the Atlantic Coast.

John Short, Pasco County sherfiff, said Rohrman's crash was the third simliar accident in his county in a week, and that he gets "report after report" of small planes taking off and landing in strange places. "They use abandoned streets or isolated highway," Short said. "It's very difficult for use to stop one of those . . . .

Drug running is done in large planes as well, particularly old DC4s, DC6s, and DC7s, piston-powered transport aircraft long since retired from airline duty. These vintage planes, however, are usually purchased legally, then flown to obscure landing sites in the United States. But they require two or three fairly well trained crew members and a good-sized landing strip. A small plane can be flown by one person not necessarly long on experience.

A pilot will get between $10,000 and $80,000 per round trip, -- depending on the cargo, the size of the plane and the pilot's negotiating ability -- for stealing a plane and flying it to Jamaica, which is only about 500 miles from Florida. That leaves plenty of profit for somebody else, because 1,000 pounds of marijuana will sell for about $500,000 on the street, according to the Drug Enforcement Administration (DEA), and the typical small plane will carry between 1,000 and 2,000 pounds.

Although planes are stolen for other reasons, almost two-thirds of those taken in 1980 were used in drug smugglikng operations, and that percentage grows as more stolen planes are recovered, according to figures at the El Paso Intelligene Center.

So far, 115 of the 241 aircraft stolen last year were recovered, not necessarily in one piece. "Many of the planes crashed," said William Small, chief of the air intelligence unit at El Paso, "and some will never be found. "If [a plane] goes into water without distress signals, we may never know of them."

The typical aircraft theft is a well-planned, carefully orchestrated endeavor, not the work of an individual. "You may have a foreign national who requires a Cessna 210," Small said. "He wil place an order with an organized theft activity. A thief will scout for the plane, steal it and fly it to the foreign national. The scout may be paid for the aircraft or provided with a load of drugs . . . ."

Thirty-one Cessna 210s were stolen last year, making it the most popular target of thieves. The 210 retails new for between $90,000 and $140,000, depending on how fancy it is. Also known as the Centurion, it is a single-engine delight that has the range (755 to 960 miles) and payload (1,200 pounds) of some light twin-engine aircraft. Because the Cessna 210 has just one engine, fuel management is less of a problem than it would be on a multi-engine plane, and single-engine pilots grow on trees.

Another common practice is for thieves to steal a number of aircraft from one location, fly them to a foreign country, change the registration numbers and sell the planes, Small said. Most stolen aircraft are used only once or twice for drug runs, then abandoned as "too hot," he said.

Richard F. Bush Jr., executive vice president of the Aircraft Owners and Pilots Association Service Corporation, which finds insurance for private plane owners, said that "in Florida, any aircraft that has the capability of hauling at least 1,000 pounds will be without insurance unless the owner already has insurance with the agent. Airplanes in Florida have somewhere around a 50 percent chance of being stolen unless they are in a barrier or have some kind of locking device."

The aviation theft bureau, set up in 1972 to deal with the stolen airplane problem, has been encouraging aircraft owners to improve the security of their machines, some of which cost up to $250,000. "Airplanes are too easy to steal," said Robert Collins, executive director of the theft bureau, "partly because security is bad at a lot of airports."

Most small planes come with simple locks on the doors and no lock on the ignition. On one popular plane, Collins said, the door will pop open when the wing is moved up and down.

"For a thief who knows how to fly, it's no challenge to take off," said the FAA's Lally.

The proper balancing of loads, including illegally installed extra fuel tanks, is a critical factor in the safety of flight, particularly with a small plane. Dangerous misloading or overloading are common practices. Investigators have tentatively identified an unbalanced fuel load as the cause of Rohrman's crash near Tampa.

One federal investigator tells of a landing strip in Colombia where many drug flights originate."Wrecks are piled up on all sides," he said. "We think, but we have never been able to prove, that some of these loads have been sold three or four times. A young, inexperienced pilot won't check his load distribution; he'll take off and the plane will crash. They'll recover the cargo and sell it to the next guy."

Assuming the takeoff is successful, the pilot will fly low to avoid radar detection once he approaches Florida, or will file a flight plan for a major airport, then cancel his plan after he is picked up on radar and tell air traffic control he is going somewhere else. Pilots of small planes do that all the time, so there is no particular reason for the controller to be suspicious.

Landings typically occur at night, on small runways sometimes bulldozed out of the swamp or on deserted highways. Landing guidance often comes from nothing more than portable strobe lights or automobile headlights.

Another typical operation involves dropping smuggled drugs from low-flying aircraft. FAA investigator Roger Jones, who works in Florida, said, "A lot of 'em end up in fatalities, where a pilot about to make a drop runs into a tree. Most of the time when they crash in flight they are pushing stuff out the door; the pilot is watching that when he should be flying the airplane."

Milford Conarroe, chief FAA representative at the federal government's drug monitoring El Paso Intelligence Center, said, "We really strongly suspect that the reason they crash is that . . . the air is full of it, and they get high . . . . They're in a confined space for a long time, the odors emanate, and fill up the breathing space. Nowadays, even when pilots are making marijuana runs, they'll pick up a kilo or two of coke [cocaione] and snort a little."