The increasing cost of fuel - natural gas, oil, and electricity - may make the home heating bills of Northern Virginia residents as high as or even higher than last winter.

Fuel costs already have risen 10 to 20 per cent since last fall, and natural gas, which heats most area homes, could jump another 5 per cent if the Virginia State Corporation Commission approves the rate increase that has been pending since the summer of 1976.

The National Weather Service's long-range forecast calls for a colder-than-normal winter, though not quite the record cold of last winter, and the Old Farmer's Almanac and the Hagerstown Almanac - which have been prognosticating such things for 185 and 181 years respectively - also predict colder than normal weather and lots of snow in the area.

Although the expected cold weather would mean high fuel bills, it is not expected to cause any fuel shortages this winter. Local fuel and utility companies say there are sufficient supplies of all heating fuels to carry the Washington area through even a severe winter, barring another Arab oil boycott:

Last winter's prolonged cold spell caused natural gas shortages in Virginia and round the nation, and many schools and businesses in Northern Virginia were closed during the height of the shortage. Pipeline companies predicted early this summer that similar shortages could occur again this winter.

However, the Washington Gas Light Co. has substantially increased the amount of gas in underground storage since then and foresees no shortages, although its 250 "interruptible" customers - large plants whose furnaces also can use fuel oil - could be forced to switch from gas to oil.

Natural gas is less expensive in Northern Virginia than it is in the District and suburban Maryland, with the average fall monthly bill for a Northern Virginia resident (using 125 therms) now $39.51 compared to $40.65 for a similar Maryland resident and $43.08 for a District resident, according to the Washington Gas Light Co.

The price of natural gas for most Northern Virginia residents has risen 85 per cent since 1972 (when 125 therms cost $21.37), compared with a 94 per cent increase for Maryland customers and 116 per cent increase for those in the District of Columbia, according to the Washington Gas Light Co.

Fuel oil and electricity both are significantly more expensive than gas as heating fuels, as can be seen from the accompanying formula for determining fuel costs prepared for The Post last fall by the Federal Energy Administration, predecessor to the new Department of Energy.

Firewood, if it can be bought for less than $60 a cord and burned in an airtight stove, is cheaper even than natural gas as a home heating fuel, as increasing numbers of homeowners are discovering. More than 10,000 wood stoves have been sold in the Washington area so far this year, and dealers say they are selling stoves and other fireplace heat savers, such as glass doors and air-circulating grates, faster than ever before.

A new pamphlet on wood stoves, for those considering buying one, is being distributed free by all Virginia county extension agents. The detailed 15-page booklet, written by Virginia Polytechnic Institute Prof. Eldridge R. Collins Jr., who has a wood stove in his own house, gives advice on kinds of stoves and their installation - most are installed in existing fireplaces. It is available by calling Fairfax County's new energy hotline, 273-8095.

However, even firewood has increased in price. Dealers here are asking $60 to $65 a cord, or more, for split hardwood, compared to $55 a cord last fall, and there are waiting lists at some dealers. Homeowners with a wood lot or access to free firewood obviously have by far the cheapest fuel.

Along with solar heat, firewood is considered one of the best fuels ecologically, since it is a constantly renewable resource. It also smells better than other fuels.

The delights and benefits of wood burning have caused area governments to warn residents about door-to-door firewood salesmen and to declare most county and city parklands off-limits to would-be wood hunters.

Fairfax County park and National Park Service officials say removing wood, dead or live, from parks is illegal. Arlington and Alexandria prohibit anyone gathering wood, flowers or other flora, except for firewood that has been cut to fireplace lengths and stacked by county or city employees. In Arlington this may be done only after permission has been granted by the park division (558-2700).

Residents buying wood are warned to beware of door-to-door salesmen peddling "ricks," "racks," or "face cords" - which are vague and illegal terms to use in Virginia, although many wood dealers still use them. A good eyeball measure of a cord would be two four-foot high rows of two-foot logs on a truck with an eight-foot wide flatbed. However, since most trucks used by wood dealers are 7 1/2 feet wide, the rows should be higher or rounded to compensate.

One of the main reasons heating bills have been rising is the increasing cost and dwindling supply of fossil fuels - oil, coal, and natural gas. Fuel oil costs 15 to 20 per cent more than it did last fall, which not only affects homeowners with oil furnaces (who now pay about 48 cents a gallon throughout the Washington area compared to 41 cents last fall), but boosts electric bills since oil is the major fuel used by electric utilities and fuel price incerases automatically are passed on to consumers.

Most Northern Virginians pay less than Maryland and District residents for electricity partly because relatively cheap nuclear power and coal provide more than a third of the electricity for the Virginia Electric Power Co., and Virginia residents thus have had lower fuel-price increases passed on to them. The gap could widen because the Potomac Electric Power Co., which supplies D.C. and Maryland residents and a number of North Arlington residents, is asking for rate increases ranging from 7.6 to 21 per cent. Vepco, which was granted a 8.5 per cent rate increase last fall, has no pending rate-increase requests.

The North Arlington customers of Pepco with all-electric homes now pay about 4 cents a kilowatt hour for their electricity (compared to about 3 cents a kilowatt for Vepco customers) and Pepco is asking for a rate boost of 21 per cent for its Virginia users. An all-electric Maryland home pays an average 3.7 cents a kilowatt and a similar District home pays 3.6 cents.

All electricity users pay higher rates for initial amounts of electricity, but the rate declines for large users such as those with all-electric homes. There are more than 54,000 all-electric homes in Northern Virginia.