PEOPLE WHO TIME THEIR INvestments using such dubious barometers as hemline lengths and Superbowl winners should consider a more reliable approach like, say, huddling with O. J. Simpson, the sports commentator.

The former halfback, who set rushing records during his football career, is now unerring at finding markets that burst into huge profits -- as soon as he abandons them. He has seen it happen three times.In 1976, he opened one of the country's first designer-jeans stores, but sold it because he "thought they were going out of style." They were actually going onto millions of people's hips.

Simpson's next retailing venture was a frozen-yogurt outlet near UCLA. But he soured on that idea, because even Californians hadn't developed a taste for it yet. They soon did, and the rest of the country followed. Undaunted, he opened a cookie store, which languished for about a year until he finally sold it. Sure enough, the cookie boom came to spread calories throughout the land.

The 38-year-old entrepreneur says his investments now include just one "totally new concept," a company that makes concert films. Simpson hedges his bets by investing in established businesses like take-out food franchises. At the same time, he avoids projects that exploit his famous name. Last year, Simpson rejected a proposal from an Iowa man who wanted to name a stud bull after him.

Naturally, a strong bull market followed.