Fill 'er up with natural gas? Maybe. As the result of a technology advance, the fuel used to heat millions of homes and factories could be powering a lot more cars in the 1980s.
Compressed natural gas (CNG) has long been used by some companies to power vehicles in corporate-owned fleets. But now a group of utilities is pushing a project it claims will put the fuel within reach of individual drivers.
The seven companies - five from the United States and one each from New Zealand and Canada - recently unveiled a new storage technology. If successful, it would enable motorists to fill their cars by tapping into the natural gas lines at their homes.
What the companies have come up with is a way to store CNG at low pressures. This enables motorists to fill their cars using modest-priced compressors similar to those in refrigerators, which would make the system far more affordable.
By contrast, existing systems pump natural gas into specially designed auto tanks at high pressures - at least 2,500 pounds per square inch. This requires compressors that cost from $5,000 to $50,000 - too pricey for the weekend driver but fine for the big fleet owner, who can quickly recoup money using the cheaper fuel (the equivalent of 60 cents a gallon in some areas of the country).
But the companies say that by filling part of the tank with activated carbon, which latches onto the gas molecules and slows them down, they can store the fuel at about 300 p.s.i.
In recent years increased conservation and competition from fuel oil have slashed industrial consumption of natural gas. The industry sees transportation as a potentially huge new market.
The number of CNG-powered vehicles in the US spurted during the ''oil crisis'' years of 1973 and '79. There are now about 25,000. Most are part of school bus fleets or utility motor pools.
There are far more vehicles in some foreign countries, where gasoline costs rival the monthly mortgage. Italy has some 300,000. New Zealand expects to have 150,000 within two years. And Canada is pushing them hard.
Natural gas has several advantages as a transportation fuel. It's clean-burning and relatively cheap. With engine modifications, it can boost a car's horsepower. There are also ample domestic supplies for a modest rate of conversions.
But there are roadblocks. One is the cost of converting a conventional car ($ 1,500), which involves a new tank and carburetor attachments.
It would cost significantly less for automakers to install the system when they built a new car. But they won't make them until there is enough demand. Ford, however, may make a few CNG trucks later this year.
''It is going to be a real tough sell,'' says Warren Heim, an engineer with Energy & Resource Consultants Inc., a Colorado firm. ''Because it's new, there is a natural tendency for people to sit back and wait to see how it goes.''
Future Fuels' new system would make the natural gas system more economical for the average driver. But it isn't expected to be on the market for a couple of years.
Then, too, further work is needed on boosting the ''range'' of CNG-powered cars, now about 125 miles.
So is natural gas going to take a sizable bite out of the petroleum-based motor fuel market? There's no agreement among the experts.
''In the short haul it will most likely just be for fleet uses,'' says Dr. Robert Sprafka, senior scientist at E:F Technology Inc., a Michigan consulting firm. Unless there's some sort of government subsidy, he adds, growth will be modest there.
But the gas industry believes 1 million CNG cars could be on the road by 1990 - a sharp rise from today but still less than 1 percent of all US vehicles. And if there were another disruption in Mideast oil supplies, those numbers could jump quickly.