In Europe they've been doing it for years. After World War II, moped riding became a common, economical form of transportation on the continent.

The moped putt-putted its way into the American consciousness during the 1973 oil embargo and has been climbing in popularity ever since. Moped sales jumped from 25,000 in 1975 to 250,000 in 1978.

With the recent energy scramble, moped fever has again hit the nation, says Joseph Wolfe, spokesman for the Moped Association of America (MAA). The industry estimates sales of 350,000 mopeds this year, bringing the total U.S. moped population to 900,000 by the end of 1979.

The two-wheeled pedal vehicle has a single-cylinder engine rated at between 1 and 2 horsepower, considerably less than that of the average lawn mower. It can produce speeds between 20 and 30 miles per hour. Most moped tanks hold one gallon of regular gas, which can take them roughly 120 to 135 miles.

"A mile an ounce" is the rule of thumb.

The rider starts the engine by pedaling a few yards before activating the motor. Once the motor is running, it remains running while the moped is in motion or idling.

A majority of moped owners are between 25 and 54 years old, with the average age 41.4 years, according to industry statistics. One in four is female, three of four are high-school graduates or better and two of three own two or more cars.

Almost 40 percent listed economy as their primary motive for purchase. Commuting distances are most often the 5-to 10-mile range.

Mopeds range in price from $350 to $800. The more expensive models might have such features as a comfort-contoured seat or stainless steel bumpers. But all mopeds are required to carry federally-mandated safety equipment including headlamps, taillamps, stop lights, reflectors and a rear-view mirror. A vehicle identification number plate located near the handlebars on the frame should specify that the moped conforms with the laws.

But all is not gas-saving glory. Mopeds can be difficult to spot in traffic, since they are easily hidden by other cars. France, which has the heaviest concentration of moped use, recored 76,642 injuries and 2,031 fatalities in 1975 as the result of moped accidents.

A mopedaler is 16 times more likely to be involved in an injury accident than an automobile driver, according to a 1974 London study. Comparable ratios for motorcyclists were 26 and for bicyclies, 12.

Injuries, however, to mopedalers may not be quite as severe as those to motorycyclists, says Lewis Buchanan, a motorcycle safety specialist for the National Highway Traffic Safety Administration.

The administration is currently revising a set of recommended moped regulations to be transmitted to each state. These recommendations are likely to include helmet, license and insurance requirements for all moped operators, Buchanan says.

The MAA recommends the following Big 5 rules for moped safety:

Learn your moped. Read your owners manual and ask your dealer to show you how to operate each control. Have the dealer adjust the moped for your size. Your arms should feel at ease on the handlebars and the seat should be comfortable enough for your feet to rest flat on the ground without stretching or leaning.

Practice starting up and shutting down the moped until you're comfortable. Learn to operate both brakes. Then take a test drive under the dealer's supervision. Practice turns and don't leave the test area until you feel confident.

2.Understand the road. When planning your route, keep in mind that all states forbid mopeds from traveling on any road which imposes a minimum speed greater than the moped's maximum speed. So interstates are out. So are sidewalks.

Try to pick a road that is relatively free of truck traffic or commercial congestion. Avoid driving too close to parked cars and their suddenly opening doors.

Watch for potholes, drainage grates and turning cars. When in doubt, let the other vehicle turn first.

3.Know the laws. Assume you are invisible and drive accordingly. Don't compete with faster traffic and yield the right of way to larger, more powerful vehicles.

Never mopedal under the influence of alcohol or drugs and never hand-carry anything. Learn hand signals, practice looking over your shoulder rapidly before changing lanes and make no sudden moves if you can avoid them.

4.Share the road. Where bright clothes and put a day-glo strips or a bike flag on your moped. Try to keep at least one car length away for each 10 mph of speed.

5.Ride cautiously or not at all in bad weather. Rain can made road slick and dangerous. Fight skids by reducing speed, avoiding sudden changes in direction, giving yourself enough distance to stop gradually and going easy on the front brake.

Turn on your lights in fog. If the fog is thick, get off the road until it lifts. Some mopedlers recommend wearing gloves. a helmet, long trousers, boots and a leather jacket.