Keeping the lawn trimmed can be a pain, especially if you end up as a casualty of your own mower.

Each year an estimated 78,000 people seek medical treatment for injuries resulting from contact with moving mower blades. Often, a person gets a hand or a foot tangled in the equipment and, as a result, loses a finger or a toe.

To reduce accidents, the U.S. Consumer Product Safety Commission has issued a standard requiring a special control on walk-behind, rotary mowers built after June 30, 1982. The control stops the blade within three seconds of the time the operator lets go of the mower handle. In most cases, that halts the blade before you can get a hand or foot near it.

In addition, the starting system has been redesigned on all new mowers to force the operator to stand away from the blade, said George Thompson, a representative for Briggs & Stratton Corp., a manufacturer of lawn-mower engines.

The first models to meet the standards appeared in stores this year, and they make mowing safer--and more expensive--than before. A random survey of area stores indicated 1983 mowers can cost as much as $50 more than 1982 models.

Toro 20672, a 1983 self-propelled, rear-bagger with the special blade-brake clutch control, now sells for $520 at Lawn & Power Equipment of Bethesda. Service manager John Hughes said the comparable Toro model for 1982 without the control sells for $470.

"Some customers come in and ask if we have any of the older models still around because they cost less money," Hughes said. "But some others come in and ask for the 1983 mowers because they want the safety features."

To comply with the government standard, the new mowers have a safety control lever, which is a bar that must be depressed for the lawn-mower blade to operate. When the operator lets go of the lawn-mower handle, the control lever is disengaged. This in turn stops the engine and the blade, or only the blade, depending on the system.

Lawn mowers now being made to meet the standard have one of three basic designs:

* Blade-brake clutch. When you release the safety control, the blade stops but the engine continues to turn. This system relies on a clutch that disengages the crankshaft and a brake that stops the blade from rotating. The blade begins rotating again when you move the safety control back into position for mowing.

* Engine-kill with electric restart. When you release the safety control, both engine and blade stop. You start the mower engine and blade again with an ignition key or starter lever.

* Engine-kill with manual restart. When you release the control, the engine and blade stop. You must restart the engine by hand each time.

Some of the new models are easy to use but many are not, according to the June issue of Consumer Reports magazine, which tested 21 new power mowers and found that the electric-restart models are among the easiest to use. The magazine also gave high marks to mowers incorporating the blade-brake clutch.

But all others tested were "inconvenient or troublesome in one way or another," the magazine said.

Ultimately, more than three-fourths of the injuries that now occur from contact with moving mower blade may be eliminated as pre-1983 models wear out and are replaced with safer mowers, federal safety officials say. Meanwhile, no matter what kind of mower you use, here are some guidelines:

* Don't mow a wet lawn. Wet grass is slippery and it tends to clog blades or discharge openings, tempting users to try unclogging while the mower is running.

* Dress properly for the job. Wear close-fitting slacks and sturdy shoes with nonslip soles. Never mow barefoot or in sandals or sneakers, which tend to slip on grass and provide little protection if you should slip.

* Before starting the mower, adjust the cutting height, check the blade condition and tighten all loose bolts. Make certain all safety devices are in proper position and that the handle attachment is secure, the gas cap is tight, the rear shield is in place to protect your feet and the grass chute deflector is secure and in working condition.

* While mowing, start the mower outside and near the area where you plan to mow. Never push a running mower on gravel. Walk-behind mowers should mow across slopes or inclines; riding mowers should go up and down.