Lee Elder of Washington, D.C., scored birdie 4 on the final home for 67-274 for his fourth and biggest PGA Tour golf victory yesterday in the $300,000 Westchester Classic.

Elder, who finished one stroke ahead of Mary Hayes, earned $60,000 for his second tournament victory of the season and pushed his 1978 official earnings to $146,348, his most lucrative. Elder was 20th on the PGA money list going into Westchester.

The victory also qualified the 44-year-old Northwest resident for the World Series of Golf at Firestone in September because he is a multiple winner, and gives him an excellent chance at a spot on the U.S. Ryder Cup team, which would make him the first black to make that squad.

When Elder won in Milwaukee in July, he qualified for the Masters for the fourth time. He is the only black ever to play at Augusta.

"Today, from tee to green, I played as well as I've ever played," Elder said. "Earlier today, I missed quite a number of putts. On the back nine they started falling. They equalized themselves.

"The World Series is something I've wanted for a long time. This is certainly one happy moment. I'm sorry that Rose (his wife and business manager) is not here."

Elder trailed coleaders Alan Tapie and Gibby Gilbert by two strokes heading into yesterday's final round. Gilbert and Tapie both faded and Elder appared to have a good shot at winning when Hayes finished 90 minutes ahead of him at 66-275.

Elder pulled even with Hayes at nine under par with a birdie 3 on the par-4 13th hole, sinking a 15-foot putt. Elder remained even with the club-house leader by parring the next four holes.

Jack Nicklaus and Hubert Green also moved into contention on the final nine but Nicklaus faltered with bogeys on the 13th and 15th holes. He finished tied with Tom Watson at 279.

Green failed to capitalize when he missed three-foot birdie putts on the 14th and 15th holes. Green birdied 17 but needed an eagle on the 18th to tie Elder. He parred the hole.

Elder came to the par-5, 509-yard final hole needing birdie to win.

His drive found the fairway and, after careful consideration on which club to hit, he selected a fairway wood and went for the green.

The shot bounced on the putting surface but trickled into the rough, pin high and 60 feet to the left of the hole. Elder's wedge shot came to rest 1 1/2 feet from the cup and he tapped it in for his biggest victory. Elder were a support stocking throughout his round to ease the pain of water on his left knee.

"I lost my chance on 17 and 18," said Hayes. He missed an eight-foot birdie putt on the 17th hole and left a 15-footer short on the 18th.

"I really didn't feel too good at the start of the day," said Hayes, who was the third-round leader at Sutton last week. "My swing didn't feel right and I wasn't putting well. I didn't expect to play that well.

"I was hitting the ball straight, but for some reason, I didn't feel good. But although I didn't feel I was playing well, I found myself three-under after eight holes. Then I birdied No. 9 and I started swinging better after that, I slowed down on the swing, I hit it solid and straight, but then I stopped making birdies. I got one at 10, but nothing after that."

Hayes, after making birdie putts of 20, 6, 15, 4 and 12 feet over the first 10 holes, missed makeable putts on 11 and 12 when the ball ran over the hole both times, and then failed again on 17.

Green finished with a 70 and was 2 strokes back at 276.

Bill Kratzert was next at 67-277.

Tied at 278 were Bob Murphy, Gilbert, Dave Eichelberger, Tapie and Dave Stockton. Eichelberger matched par 71 under threatening clouds, while Murphy had a 69, Tapie and Gilbert 73s. The scrambler Stockton chipped in four times on the way to a 66.

John Mahaffey, a winner his last two times out, shot 75 and was far back at 287. Andy North, the 1977 Westchester winner and current U.S. Open titleholder, was 71-283.

Nicklaus, the only two-time winner of the Westchester, has said this may be his final PGA stop of the year, although there's a possibility he'll play in the World Series.