How much does it cost to operate your car? More than you may think.

The American Automobile Association has updated its "average" figure. It is useful only as a reference point. To work out your own cost, make appropriate adjustments in the categories in which you vary from the norm.

An average car (intermediate size) retained for an average length of time before trade-in (four years) and driven an average distance (10,000 miles each year) will costs its owner $1,964 per year - or 19.64 cents per mile. Parking fees, turnpike tolls, bridge tolls, repairs and traffic fines are extra.

Fixed costs (license and registration fees, taxes, depreciation and insurance) will average $1,402 (or 14.02 cents per mile if the $1,402 overhead is spread over 10,000 miles). You can't escape fixed costs, even if your car is parked in your own driveway all year.

Running costs (gas, oil, tires and routine maintenance) average $562 per year for 5.62 cents per mile. Note that the AAA mentions "routine maintenance" but not repairs. If you dent a fender or your transmission conks out the day after your warranty expires, you're no longer average. Add something to your totals.

If you own a small auto, keep a car longer than four years, or drive more than 10,000 miles a year, your cost-per-mile figure will go down. If you own a luxury car that depreciates $10 every time you look at it, or if you trade for a new car every year or two, or drive less than 10,000 miles a year, your cost-per-mile figure will go up. But whatever your individual adjustments to the "average" cost, the bottom line is still going to be borrendous. Owning an automobile is not cheap.

Sad to say, the alternatives to owning an automobile are also unattractive. Per-mile costs by taxicab are higher than in private autos. Bicycles, mopeds and motorcycles provide relatively cheap transportation but are not considered suitable by many commuters for a variety of reasons: saftey, convenience, comfort, age and/or physical condition of operator, weather, distances involved, etc.

For many people, the only practical alternative to owning a car is mass transit - especially the new subway, which usually offers speed and comfort in addition to lower per-mile costs. But mass transit has some hidden costs that must be taken into account before comparisons are made.

In most major cities, transit systems have been taken over by public agencies, and new facilities have been built at great expense. In one way or another, the public has had to pay for construction, rolling stock and operating deficits. Even the motorist who never uses mass transit must pay part of mass transit's costs, as well as his own cost of automobile ownership. This makes it difficult to compare the per-mile cost of public and private travel.

Nevertheless, we know that in addition to readily visible expenditures like those for gas and parking, the auto commuter pays substantial sums for depreciation and other hidden costs. Similarly, in addition to the farecard price of a subway ride, we all pay substantial sums in taxes to subsidize transit hardware and operations.

To whatever extent regional taxes are reduced by federal grants to a local transit authority, federal taxes must be increased to make those grants possible.

So, either way, nobody gets a free ride. Mass transit may be cheaper than auto travel, but it certainly isn't cheap.

Only Freddie Laker offers a relatively economical way to get from here to there, but unfortunately Freddie's airline doesn't fly from McLean to the Pentagon, nor does it offer service between Silver Spring and the Federal Triangle.