Washington area consumers should act now -- if they haven't already -- to prepare their homes' heating systems for efficient operation and guard against breakdowns during the cold days ahead, local officials say.

Checkups or routine maintenance inspections are advised "so if there are serious problems, there's enough time to repair them," said Susan Butz, a representative of Washington Gas Light Co. She and other officials noted that it can be difficult to get quick service if a furnace fails during the peak heating season.

Roughly 55 percent of Washington area households heat with natural gas. For thosewho do not have their units serviced by professionals, WGL has a leaflet that explains how to turn the furnace off, check the blower, oil the motor, inspect the burner and then turn the furnace back on.

The WGL service department does some free diagnostic furnace work, but it doesn't perform any furnace maintenance or repair. Nor does it light the furnace without charge.

The company offers some special notes of warning:

* Make sure the gas furnace is properly vented to the outside of the building. The chimney and flue pipe should be in good condition and provide a good draft.

* Do not use a gas range to heat a home. It could result in the production of dangerous amounts of carbon monoxide.

* Do not try to repair or install your own furnaces. It is illegal in most areas.

* Keep areas near the furnace free of paints, solvents, papers, rags and other combustibles.

About 33 percent of area households heat with oil-fired furnaces, the second largest category. (Ten percent use electricity, with the remainder of area households relying on bottled gas, coal or wood.) Oil suppliers typically also have contracts to provide annual maintenance for the heating systems they furnish with oil, according to John Talbott of the U.S. Department of Energy.

"The standard oil furnace checkup by the contractor takes care of most concerns -- cleaning the burner and getting rid of soot and buildup," Talbott said.

After checks of the furnace itself, experts have a few other suggestions:

* If you have a forced-air furnace, the filter should be checked at least twice a year. Change disposable filters when they get dirty or clogged. Permanent filters can be washed in warm water and detergent, rinsed, dried and replaced.

* If you have a hot water boiler, insulate the boiler, the hot water tank and hot water piping in unheated spaces. Clean radiators or baseboards, also.

* Set the thermostats at 68 degrees during the day and 65 or less at night or when the occupants are away for a weekend or vacation.

Additional energy-saving suggestions are: make sure that insulation is adequate, install storm windows and doors, make sure furniture or curtains don't block heat or cold air registers, close the fireplace damper when the fireplace isn't in use and keep curtains and drapes open during the day and closed at night.

Consumers who need a licensed plumber or heating contractor may be able to check on the firm's reputation by calling the consumer agency in the jurisdiction in which the firm is located. Most area consumer agencies will provide information on the company to consumers asking for help.

In addition, the Montgomery County Consumer Affairs Office has compiled a list of 32 local heating and air conditioning firms favorably recommended by area residents.

Barbara Gregg, the agency's director, said the list -- available at many libraries -- provides consumers with an additional tool for finding a company to do heating and cooling work for their homes. She said people should continue to shop around, get estimates and obtain written contracts to avoid problems.