He's 74, wears red sneakers, a yellow cap and suspenders. He earns his living by digging graves and, until a year and a half ago, he bicycled to work each day. But now Horace Ferguson is taking life a little easier - he's given up his bicycle for a bright yellow moped.

Ferguson is one of an estimated 275,000 Americans who have bought mopeds, a 95-pound cross between a bicycle and a motorcycle, and helped make them the latest fad.

"I saw this elderly lady riding by one day," Ferguson said, "and I ran after her to find out where to get one." Ferguson said he couldn't catch up with the woman, but later saw a moped in a store. Within a day he plunked down $335 to buy it.

Ferguson, who lives in Alexandria, said he carries his tools on his moped when he is working and transports his two grandchildren on his days off.

The motorized two-wheelers seem to be gaining popularity. Only 25,000 were sold two years ago, their first in the American marketplace, but about 150,000 are expected to be sold this year, according to the Motorized Bicycle Association, the moped dealers trade group.

Along with popularity controversy has come over mopeds' safety and questions about whether they should be regulated as motorcycles, bicycles or in a class by themselves. Some motorists have complained to Washington-area police departments and governing bodies that mopeds, which can reach a top speed of 40 miles an hour, impede already congested traffic.

Max Jones, a driver training instructor in Prince George's County, said he is concerned that some moped owners are "souping up" their machines.

"You give a kid something and he'll make it go faster," said Jones, adding that he knew of no Maryland law preventing such modification.

Jones said he was particularly opposed to younger children being allowed to use mopeds because the youngsters might not be able to control them.

"What about some of these bike trails used by joggers?" Jones asked. "A guy (on a moped) may be doing 450 m.p.h. and run over a jogger." He also criticized the fact that Maryland does not require moped users to have liability insurance, although moped users are forbidden from driving on controlled access roads or on highways with speed limits above 50 m.p.h.

Moped proponents, of course, tell a different story. They claim mopeds, costing between $335 and $570, are safer than 10-speed bicycles because they meet the safety requirements of motorcycles. The mopeds have rain-resistant drum brakes, wider tires that don't get wedged in railroad tracks, a strong headlight and a motor that makes it easier to avoid weaving when traveling uphill.

Among moped owners and advocates are physicians, teachers, security guards, bartenders, fire fighters and a filling station in Annapolis that puts a jumper cable in one basket and a battery in the other and sends the bike out to rescue stranded motorists.

Bill Topolski, owner of General Moped in Alexandria, heralds the moped as the "solution to everything" - energy, pollution, noise, parking, traffic. He and other dealers said much of the mopeds' popularity may be attributed to their gas mileage - 150 miles to the gallon.

Sarah Wickham, a 16-year-old Alexandria resident, said she regards her moped as a sound economic investment. She uses it for a messenger service she owns and operates. "It's fun to ride and to park it all I have to do is put it on the curb," she said. "The only pitfall is that at the tops it only goes 25 to 30 m.p.h."

While the mopeds have grown in popularity, local governments have had difficulty in determining how to classify the half bike-half motorcycle.

Classification as a motorcycle can force a moped owner to buy tags and licenses, pay title and inspection fees and insurance premiums and be a certain age to operate the vehicle. If mopeds are classified as bicycles, the owner will likely only have to register the vehicle.

Both Maryland and Virginia classify the moped as a bicycle, while the District defines it as a motor vehicle - a distinction which requires owners to pay a $6 vehicle tax, a $3 inspection fee, a $5 title fee, a 4 per cent excise tax on the purchase price and obtain a driver's license.

But even in Maryland and Virginia the moped doesn't fall under the same law as its two-wheeled cousin the bicycle. In Virginia, a moped is a moped unless it exceeds 20 miles an hour and then it becomes a motorcycle. Riders are also required to be at least 16 years old. A driver's license is required in Maryland.

Paul Zimmerman, a spokesman for the Motorized Bicycle Association, said most states are resolving the moped identity problem by creating a new legal category for the bike. He said 31 states have moped law.

Entering the District on a moped from either Maryland or Virginia can be not only difficult, but may involve crossing the legal twilight zone. Police officers in the District say mopeds must abide by D.C. law, which requires drivers to have either a moped, motorcycle or can license and a tag on the moped.

Several Virginia and Maryland moped riders have complained about the D.C. tag requirement since tags are not required in their home jurisdictions. District police officers say they would probably give the owner of an untagged moped a warning and then a citation for a second offense.

Vernon Gill, general counsel for the D.C. police department, said a decision will be made soon on requirements for moped commuters. He said that because there is a narrower definition of the moped in the District, some people owning mopeds in Virginia or Maryland would have to register them as motorcycles in their home jurisdictions in order to drive in the District.

Topolski the Alexandria moped dealer, criticized the District's action in stopping Virginia moped riders without D.C. tags. He was also critical of a District law - which he said is the only one of its kind in the natio n - requiring moped dealers to be licensed as motorized vehicle dealers and each salesman to be bonded as an automobile salesman.

Topolski, Zimmerman and others interested in the moped industry said they would like to see a uniform, nationwide moped law.