There's no scientific way to describe it, no method to measure its mystique - but Harley-Davidson Inc. contends the sound uttered by its legendary V-twin motorcycle engine is so distinctive it deserves a trademark.

"The sound we like to use, the verbal description, is, very fast, `potato-potato-potato,' " said Joseph Bonk, the company's trademark attorney. "It brings the imagery to mind."Just like IBM obtained a trademark for its computers and Jell-O secured so no one could copy its gelatin dessert, Harley wants federal protection from imitators.

"There are people trying to duplicate the sound," Bonk said.

But there are opponents standing in the way, including rival motorcycle makers Honda Motor Co. and Yamaha Motor Corp., who argue Harley's claim is unfounded and have filed opposition papers to its application with the U.S. Patent and Trademark Office.

"Yamaha has been building V-twin engines since the early '80s, and there's no difference between the sound their engine makes and the sound our engine makes," said Yamaha spokesman Bob Starr. "All V-twins, by their nature, have two pistons. The pistons go up and down and they all sound the same."

Honda contends it has long sold heavyweight bikes that produce an exhaust sound similar to the Harley motorcycles.

The sound doesn't identify and distinguish Harley's motorcycles from others or "indicate the source of the motorcycles," Honda's notice of opposition claims.

But Harley begs to differ, contending it's easy to identify that potato-potato-potato, even in a crowd.

"It's something our customers, and other riders and non-riders alike have begun to identify," Bonk said. "They identify the sound and they relate it to that brand image."

Mike Keefe, director of the 296,000-member Harley Owners Group, said the engine sound is "a very important element of the motorcycle."

Harley-Davidson - a company that started in a Milwaukee shed in 1903 and survived bankruptcy, years of quality problems and a Japanese invasion of the market in the early '80s - seriously cultivates its brand image.

Years of production problems have kept supply well below demand, but Harley is gearing up to produce 100,000 motorcycles annually by the year 2000. Its $1.5 billion in annual sales have given it some cash to pursue long-neglected trademarks, Bonk said.

Harley's application is charting new ground. There are only a few dozen sound trademarks in the United States and unlike the MGM lion's roar and the NBC chimes, Harley's sound is linked to mechanical function, said Ruth Nyblod, a spokeswoman in the Trademark office.

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"The bottom line is, would our registering this mark cause confusion in the marketplace among consumers? We've already made that decision, that it's probably registerable," Nyblod said.

With provisional approval on Harley's side, the nine registered opponents bear the burden of proving the engine sound is neither unique, nor closely associated with the Harley brand. The dispute could last for months.

The U.S. Supreme Court has been leaning heavily toward protecting intellectual property such as trademarks and Kenneth Port, a law professor at Marquette University, for one, believes Harley's guttural blasts will be registered.