If any further evidence were needed that the strength in American racing has been shifting from East to West, Island Whirl provided it today.

The 4-year-old colt had been one of the lesser stakes horses in California; he had not won a stakes race for nine months. But this afternoon he demolished the best older horses in New York, running away to a five-length victory in the $227,500 Woodward Stakes at Belmont Park.

Jockey Angel Cordero Jr. sent Island Whirl to the lead at once, set a slow pace, opened a commanding seven-length lead and finished the 1 1/8 miles in a swift 1:46 4/5. Silver Buck, considered the best 4-year-old in the East, never remotely threatened him as he rallied to finish second. Longshot Silver Supreme was third.

If this race will not be remembered for any special drama, it may be the most vivid illustration of the way California horses are starting to dominate the sport. Last fall John Henry came East and wrapped up the horse-of-the-year title at Belmont. Throughout this season West Coast horses have been winning major stakes here.

Island Whirl is only the vanguard of a western invasion this fall. Perrault, the winner of last week's Arlington Million, is expected to come here for the Marlboro Cup two weeks from now. And John Henry may run in the Jockey Club Gold Cup.

This trend, however, was lost on the chauvinistic New York racing fans who had sent Island Whirl to the post at odds of 11 to 1. But they would have upgraded his chances if they could have had a sneak preview of the first quarter-mile of the Woodward.

Island Whirl was clearly the speed of the seven-horse field; he had won a six-furlong race in a blazing 1:08 3/5 at Del Mar last month. None of the other speed horses in the race wanted to battle with him early, so Cordero was able to get to the lead while covering the first quarter mile in a leisurely 23 3/5 seconds.

"I didn't have to plan anything, just play it by ear," Cordero said. "After he broke on the lead he relaxed pretty good. When he relaxed down the back side I knew we were in good shape."

Island Whirl covered the half-mile in :46 2/5 and the three-quarters in 1:10, with Wavering Monarch and World Leader stalking him. The two 8-to-5 shots, Silver Buck and Winter's Tale, lay farther back and kept an eye on each other.

After three-quarters of a mile, both favorites started to move. Winter's Tale didn't have much to give; he accelerated for only about an eighth of a mile and then faded to finish fifth. Silver Buck couldn't gain on Island Whirl, either, because the leader was in high gear at that point, too. Island Whirl ran the fourth quarter of the race in 24 seconds flat, and it is virtually impossible to catch a horse moving at that pace. Silver Buck couldn't come close.

Island Whirl paid $24, $7.60 and $5.20. Silver Buck returned $4 and $3.40, and Silver Supreme paid $8.40.

The winner earned $136,500 for owner William C. Harder of New York, and became eligible for the $1 million bonus that goes to any horse who sweeps Belmont's fall championship series -- the Woodward, Marlboro Cup, and Jockey Club Gold Cup.

But things are not going to get easier for Island Whirl. He will probably have to meet Timely Writer, the good 3-year-old who skipped this event to run in an easier spot on Monday. More ominously, he is going to have to face the top-flight horses from the West Coast who figure to dominate the rest of the major fall races. Racing Returns to Bowie

Thoroughbred racing will return to Bowie Race Course Tuesday when the 36-day fall meeting begins at 1 p.m.

Racing will take place at the one-mile track Monday through Saturday through Oct. 18, including the $100,000-added Governor's Cup Handicap on Oct. 9. The $40,000-added Marlboro Nursery, filly division, a seven-furlong event for 2-year-olds, will be run on opening day.