LOS ANGELES (AP) _ A young motorcycle enthusiast's design for a shock absorber was stolen by the Suzuki Motor Co., a jury has ruled, awarding the inventor royalties that could total $19 million.

Don Richardson of Pine Grove, Calif., is entitled to worldwide royalties of 50 cents for each Suzuki motorcyle sold, the jury said Friday. And Suzuki also owed Richardson $12 per motorcycle for appropriating two trade secrets, it said.

Since 1981, Sukuki sold up to 1.7 million motorcycles that the jury found relied on Richardson's susension system.

The six-week trial in federal court capped a seven-year patent battle.

Richardson, now a 31-year-old building contractor, was 19 when he first built prototyes of the floating suspension system, which allows the bike to travel more smoothly and rapidly over rough terrain without bottoming out.

''Suzuki just couldn't acknowledge that a young, American garage inventor could actually do better than their in-house people. This trial has proved them wrong,'' said Richardson's attorney, Theresa Wagner Middlebrook.

Lawyers for Suzuki said they may appeal the verdict.

Richard W. Driscoll, another of Richardson's attorneys, said Richardson did much of the design and development of the shock absorber on his own, spending his college tuition money to form a company with a partner, Guy Cazort.

Suzuki eventually approached Richardson about developing his invention for commercial use on its motorcycles, Driscoll said. The company signed an option contract with Richardson that would allow them to use the device if it proved adaptable.

Suzuki even flew Richardson to Japan and put him in contact with in-house engineers for the final development work.

''They were doing the final adjustments in 1979, when headquarters advised him they had terminated the option. ... It turned out they had been secretly testing their own version,'' Driscoll said.

Suzuki began production of two ''full-floater'' models in 1981.

Evidence introduced at the trial showed that Suzuki engineers took notes on Richardson's plans for the suspension system, then altered their notebooks after he filed his patent suit in 1980.

Suzuki's lawyers said they canceled Richardson's option after learning his floating suspension system was very similar to other suspension systems used over the years - enough so that they believed his 1974 patent was not valid.

However, U.S. District Judge William P. Gray ruled earlier in the trial that Richardson's patent was valid.