General Motors Corp. is planning to build electric automobiles.

If it happens - the past five years have taught Detroit's auto makers and others just how uncertain anything can be - the GM electric model will:

Weigh 1,700 to 1,800 pounds, have a wheel base of about 90 inches, and measure 150 inches overall.

Have a top speed of about 55 miles and a comfortable range of 100 to 150 miles a day.

Be designed to plug in nightly for recharging.

Carry two adults handily, plus groceries.

Be strictly a city car . . . no trips for the GM electric, at least initially.

Be priced at $5,500 to $6,000 in 1977 dollars.

The oil embargo, federal legislation, and the economics of the auto industry are behind GM's newborn optimism about electric car is well into the deadly serious planning and design process that precedes production.

When will the GM electric be ready? It could be as soon as four years, and GM is shooting for no later than seven years . . . as a 1985 model.

Industry observers point to three public pronouncements by GM executives this year as proof of the auto maker's seriousness about electric cars.

On February 17, Howard H. Kehrl, executive vice president in charge of the corporate technical staff, presided at a press conference about energy. He and other GM executives talked matter-of-factly about limited world petroleum supplies.

Asked how GM would operate when the nation and world runs out of oil and gasoline, Kehrl said GM has "several thousand engineers and scientists trying to figure that out. I guess we're pretty convinced there will be personal transportation and we intend to be in the business of providing it."

"If you can use nuclear power to generate electricity," he said, "then you can have electric cars."

On May 11, Robert Lund, a GM vice president and general manager of the Chevrolet division, told a reporter from the Daily Oklahoman newspaper in Oklahoma City that the "second car in many families would likely be an electric car, by the mid-1980s."

While "every kind of fule or propulsion system that is known to the industry" is on the drawing board, the electric car "has the best chance to succeed" as an alternative power source, Lund said.

By 1985 battery size and power shortcomings will have been resolved and electric cars will even offer air conditioning, he said.

On May 23, Elliott M. Estes, president of GM, told the Econimic Club of New York that one kind of new technology GM "is excited about . . . is the progress we've made toward building an electric car that is suitable for use as a shopper or commuter vehicle in two- or three-car families."

Estes said GM has made "good progress" in the laboratory on the chemistry of a zinc-oxide battery as well as making the conventional lead-acid battery lighter in weight and more potent in the electrical capacity.

The automaker has also "just started a pilot operation . . . to learn how to manufacture the battery and solve some other problems it still has," Estes said.

His comments, it shouls be noted, were the only remarks of the three that were carefully reviewed by GM's legal and public relations staffs. But Estes' unexpected reference to electric cars were lost in news reports about GM planning to use three-way catalysts in some 1978 and most, or all, 1982 cars.

As the trade newsweekly Automotive News pointed out, to anyone sophisticated in the arcane ways of the auto industry, the relative importance of the converter announcement eclipsed GM's more important pronouncement about the electric car.

It's fair to speculate tha if Estes had delivered the talk to the Economic Club of Detroit the comment about catalytic converters would have been lost in the welter of headlines about electric cars.