Keith Fergus rolled in a 20-foot putt on the 18th hole yesterday to force a sudden-death playoff with Rex Caldwell and then parred the first extra hole to capture the $375,000 Bob Hope Desert Classic in Palm Springs, Calif.

Fergus' third consecutive seven-under-par 65 set up the third tournament victory of his six-year PGA career. The final round was contested on the La Quinta course.

Fergus won $67,500. Caldwell, who also shot 65--335, earned $40,500.

"I decided just to come out and have some fun this year," Fergus said. "I think I'd been too serious about the game in recent years. Heck, if you can't come out here and have fun, what's the sense playing?"

Caldwell virtually gave the tournament away on the playoff hole, the par-3 15th, when he ripped his tee shot into some trees on the right and had to hit out left-handed with his putter. He left the ball 25 feet from the hole and missed the putt.

Fergus' tee shot stopped 20 feet from the pin and he two-putted to clinch the victory.

Fergus appeared to have lost the tournament on the 16th hole when his drive landed in a pond and he carded a bogey 5. Caldwell, playing in the group ahead of Fergus, then took a one-stroke lead on the 17th hole when he dropped a twisting 25-foot putt, pumping his fist to the sky in celebration.

But Fergus cut the celebration short on the 18th green, holing his long birdie putt as the gallery erupted and Caldwell, watching from the fringe, closed his eyes in frustration.

John Fought, who began the day with a one-stroke lead over Fergus, Caldwell, Craig Stadler and Raymond Floyd, struggled to a final-round 71 and finished at 20-under-par 340, tied for fourth place with Chip Beck, who shot a 68.

Stadler, the 1982 Masters champion, shot a three-under 69 and finished in third place at 339. Floyd, winner of last year's PGA Championship, closed at one-over 73 and in a three-way tie for fifth at 343 with Bob Gilder and Tze-chung Chen, who had the day's low round of 64.