Lee Elder, the Washington, D.C., golf pro who was the first black man to play in the Masters, said yesterday he will retire from the PGA Tour in July 1984 to play on the fast-growing Seniors tour.

"As soon as I turn 50 next July and I become eligible I'll start devoting most of my playing time to the Seniors tour," Elder said after shooting 72 in the second round of the Kemper Open at Congressional Country Club. "They're already playing for $5 million in purses on that tour and that's as much as we were playing for when I first came out here, so it's perfect for me.

"I'll still play a few PGA tournaments like this one and the ones I've won in the past. But basically, I'll only play the courses that I really like."

Elder shot 151 his first two rounds at the Kemper, missing the cut by one stroke, after a maddening 79 on Thursday brought about by horrendous putting. After finishing with 42 on the back nine, including four three-putt greens, Elder walked off the 18th and tossed his putter into the lake adjacent to the green.

"I was frustrated because I couldn't believe I could play so bad," Elder said yesterday. "I had gone back to that putter twice in the past so I figured if I tossed it in the lake I wouldn't go back to it."

Using a similar putter yesterday, Elder putted much better. His only real problem was with the new driver he has been trying out. Time and again, Elder was in trouble to the left off the tee, most notably at the fourth hole, his 13th of the day, in which he took a double-bogey 6.

"If I miss the cut, that will be the hole that did it, regardless of how poorly I played Thursday," he predicted before the cutoff of 150 was announced.

But Elder's ball rolled over a hill and under a small pine tree. From there he was able to push up against the tree and half-swing a punched five-iron. But he got under the ball a bit and it caught a tree branch and failed to reach the fairway.

Still in the rough, Elder pushed an eight-iron shot into the trap to the right of the green. At that point he showed his frustration for the only time all day, walking up the fairway and cursing softly to himself.

"That hole took the run out of me," he said. "After the third I was thinking I had some birdie holes coming up and I could shoot 69 or 70 and at least definitely make the cut."

Elder knew yesterday he would be around today, anyway. Frank Chirkinian of CBS-TV, which televises the last two rounds, had asked him to do some on-air work for the network over the weekend. Elder agreed to work today, preferring to practice Sunday for Monday's U.S. Open qualifying.

Regardless whether he made the cut, Elder felt much better about his game after the second round than the first. He did, in fact, have a couple of birdies in him even after his disaster at the fourth.

He rolled in a 10-foot putt for a 4 at the 542-yard sixth and then, after a nice save from the sand at No. 7, he made another 10-footer for birdie at the eighth. On his last hole, the 602-yard ninth, Elder's 25-foot birdie putt slipped by the hole on the right at the last second.

Although he has been experimenting with his game a lot lately--new driver, different putters, new stance--Elder has been making a comeback this year after a poor 1982 season. Last year, Elder won $33,602 and was 115th on the money-winning list. If the PGA had not gone to its 125-man exemption list, Elder would have lost his exempt status for the first time since 1975.

"I worked hard early this year, played a lot out west and came out of there feeling confident, even though I didn't have any real great finishes," he said. "My goal this year is to win $100,000 so I'll have $1 million in career earnings."

Last month, Elder finished in a tie for second place in Houston behind winner David Graham. It was his first top-10 finish in two years and put his earnings for the year at almost $46,000. He has won $955,000 since joining the tour in 1968.

Elder has won four tournaments in his career, the last in 1978. He says he would love to win again before he joins the Seniors for reasons both pragmatic and sentimental.

"I'd love to win because winning does terrific things for you in endorsements," said Elder. "But more than that, I'd love to have that feeling of beating the best again. That's the best feeling I've had out here."