Automobile advertising can be a very peculiar business.

For instance, there was the time the auto executive wanted to film a commercial with his company's car tumbling down a mountainside, smashing into a rocky abyss to prove that it could withstand the impact better than its competitors. That one never made the air.

Then there was the ad in which one company boasted that its car was better than six others in driving up the Bromley Mountain ski slope in Vermont.

And there's always the automobile executive who just knows his car can outperform the others, but actual tests don't bear it out.

"Many times, what an advertiser wants to say, he can't say because his car won't do it," said Harley E. Holt, whose independent automobile testing company, hidden in two rooms of an unassuming 18th Century house in Leesburg, is the backbone of many automobile company's claims.

Holt and five employes in his American Testing Institute perform numerous tests that yield data most of the 27 imported car companies and others need to put their best wheels forward.

Like the Ford Motor Co. campaign three years ago: "Can a 1976 Ford Granada match the smoothness and quiet of Cadillac Seville and Mercedes 280... with a sticker price under $4,000?" Ford executives "said they could feel it in their seats" that Granada's ride was as smooth, but they needed the facts to back it up, Holt said.

Holt devised a test using scientific shock and vibration equipment that would show visually one of the components of a smooth ride.

"I will not do things like crack a diamond in the back seat of a car, or break light bulbs with a stick sticking out of the side of a wheel" to demonstrate a calm ride, Holt said. Nor would he place nitroglycerine in the car to show that it didn't explode because of its level performance.

Holt's company, formed nearly five years ago, is one of a handful that perform scientific tests necessary for the companies to make certain claims in advertisements.

While other companies may perform auto tests on the side, Holt says his is the only one specializing in them. Holt and the other companies don't actually do the commercials. He maintains that helping a company document and package its mechanical attributes is not deceptive because ATI doesn't hide any of the car's failures. It only drives home the best features.

The tests usually are required to satisfy the major television networks and advertising agency lawyers who demand documentation before commercials can go on the air.

"We try to get involved in their initial thinking," Holt said. The companies ask, "'What do you think (the car's) strong points are?'" Holt said. "We work with the advertiser and the company with ideas they can use in the marketplace" such as a car's handling or speed.

On a clear day, ATI may utilize a little-used airfield in Upstate New York or Palm Beach International Roadway in Palm Beach, Fla., for its driving tests. Professional drivers can be seen driving cars round and round in circles until they skid or spin out of control, or racing down slaloms, knocking down fluorescent cone after fluorescent cone until the car's optimum performance is recorded.

Holt's company was behind the wheel of the recent Volkswagen commercials dramatizing how cheaply one can drive from New York to Los Angeles in a Rabbit subcompact. Holt's driver went the distance for eight days, keeping data such as toll costs, and oil and gasoline bills.

Some companies use Holt's services just to determine where their cars stand with their competition, what changes should be made to improve performance and what selling points their dealers should emphasize, Holt said.

The cost of Holt's services range from $500 to about $50,000 Many companies use his services three to four times a year, he said.

ATI basically executes two tests. Static tests measure leg room, trunk room, head room and other physical dimensions. Dynamic tests measure performance such as acceleration, braking and handling.

Testing grounds must be flat and dry, and the cars -- usually bought or leased by ATI at the company's expense -- must be representative of the line and have engine parts set according to manufacturers' specifications without options. No souped-up versions are allowed, Holt said.

The best sample of cars would be about 15 or 17, Holt said, but the expense prohibits that. Three to five cars of the same type are used instead.

Even new tires, called green tires in the trade, cannot be used but must be driven between 200 and 500 miles first. The car itself must be broken in according to the manufacturers published recommendations. Everything is done in uniform laboratory conditions, Holt said.

The tests are performed numerous times for hours and days. Sometimes the companies are disappointed because their claims can't be documented scientifically.

"A lot of times we've finished, written up a 30- to 40-page report and (the company) can't use it," Holt said.

Three tests most often used to determine a car's handling are the skidpad, slalom and the lane-change tests. Although a car may surpass all others in these three tests, the company cannot claim its handling is better overall than all others, only when measured in the specific tests.

During the skid-pad test, a car is driven around a 200-foot circle until it either skids or spins out of control.

The slalom test measures how fast and at what intervals ea car can weave in and out of specially placed cones. Holt uses photoelectric timers to verify the data. "A lot of cones get knocked over and torn up," Holt said.

The double-lane change measures how well a car can maneuver around an obstacle when the car will not stop after applying the brakes.

"I've had an all-consuming interest in cars since I was 14," said Holt, 38.

I was interested in racing and sports cars when I was young." Holt said he even dabbled at racing for a while but realized he would never be good enough. "I'd have to get involved in cars some other way," he said.

Holt received a bachelors degree in mechanical engineering from the University of Virginia and worked as an engineer for a Riverdale, Md., firm that designed aircraft simulators.

He later became a test engineer for the General Environments Corp. in Alexandria where he was involved in aerospace environmental testing. He and the company researched safety standards for cars and became involved with automobile crash testing. In 1974, he formed ATI.

Although the testing is done else-where, the inspiration comes from the Leesburg office, the walls of which are spotted with drawings of cars, photographs of cars, a plastic model racing car and even three foreign car pin-up calendars.

Even a card from Holt's wife summed up his automotive drive: "Valentine, I guarantee I love you forever, or after 24,000 miles, whichever comes first."