Darrel McHargue, who has become one of the country's most successful jockeys while competing on the West Coast, came East for a day and demonstrated just how he had done it.

He gave a masterful performance as he rode John Henry to a half-length victory in the $169,250 Hialeah Turf Cup today.

John Henry had compiled an excellent record in California, but basically he is a front-runner and he was attempting to go 1 1/2 miles for the first time in the Turf Cup. McHargue helped him do it.

The gelding broke sharply and obviously wanted to go to the lead, but McHargue restrained him and let let longshot Houdini have the early advantage. As they ran down the stretch for the first time, McHargue steered his mount toward the middle of the track and let another horse go past him. "That set it up for us," he said. "It put us in the garden spot."

Poised outside the two pacesetters, with clear running room, McHargue had the option of moving to the lead whenever he wanted. He spurted to the front on the final turn, just as the stretch runners in the field were getting into gear. Dancing Master, a 16-to-1 shot, closed with a rush but missed overtaking John Henry by half a length.

"The winner was lucky," said Jean Cruguet, Dancing Master's jockey. "He had everything his own way. He won't beat me again over the mile-and-a-half distance."

John Henry returned $6.60, $4.60 and $4.80, while Dancing Master paid $8.20 and $6. Ivory Hunter, who finished another five lengths back, returned $25.40 to show.

Producer, the European filly, who went off the 7-to-5 favorite never threatened and finished seventh, starts this year for I'm It. He earned $52,290 for the owners, the Lightning Stable, which increased his bankroll for 1980 to 67,990. Last year, I'm It won $28,740 with four victories in 10 starts, mostly in claiming races.