The luckless Tournament Players Championship fired another blank today as morning rains ruined the chance for a marathon 36-hole finale. Instead of a golfing equivalent of "They Shoot Horses, Don't They?," this troubled event, which has been weather-battered throughout its seven years here, managed only to complete 18 holes of third-round play.

When this TPC is concluded Monday--minus live national TV coverage--the last round will offer a wealth of worthy possibilities; call it Young Lions pursued by Gentle Ben and Golden Bear.

Rarely have so many promising young players risen to the top in one week. The leader board here is dominated by five close friends, all of whom have been waiting for the day when they would make the tour their private, profitable property.

"Nature is going to have its way," said young John Cook, whose 71 for a six-under-par total of 210 gave him a one-stroke edge over Bobby Clampett (70). On Clampett's heels in third place is Vance Heafner at 69--212. Peter Jacobsen (72--213) and Hal Sutton (70--214) complete a quintet of relatively new names, all with blue-chip amateur credentials.

For those who like more familiar names in the drama, the usually snakebitten Ben Crenshaw (69) is part of a fourth-place trio at 213, just three shots back, while Bruce Lietzke (71) is tied with Sutton.

For dreamers, there's also the remote possibility that Jack Nicklaus, who suddenly seems to have found his game, could pull a swamp miracle. The Bear shot this day's low round of 68 and is in 16th place at 217. After his 32 on the the back nine, Nicklaus said, "That's the closest I've ever come to nine birdies on nine holes. I hung four in the edge. If I shoot 67, I still have a very good chance to win."

Much more likely is a final-day shootout among the young bloods--Cook, Clampett, Heafner, Jacobsen and Sutton--plus, perhaps, Crenshaw.

"I looked up at the scoreboard and thought I was back in the Porter Cup when we always seemed to be on top together," said Clampett, referring to one of the sport's top summer amateur events. "We always wondered how, if it had been a pro event on the same course, not amateur, how would we have done?

Now, they know. The pro world is theirs for the conquering--at least the Players Club portion of it.

No one could hardly seem more confident than Cook or Clampett.

"That's about as solid a round as I can play. I can't hit the ball much better," said Cook, who birdied the first and 17th holes with 15-foot putts, but bogeyed the sixth when he drove into the trees and had to swing a putter left-handed to swat the ball a few feet back into the fairway.

Though Cook's swing was sound, his putting showed signs of encroaching nervousness; had he not missed five dead-level birdie putts between six and 12 feet, Cook might have a lock on the $126,000 first prize.

Clampett, who has his residence here, seems even more sublimely grooved, parring the first 11 holes, then refusing to lose his poise after making bogey from heavy fringe at the 336-yard 12th. Clampett responded with birdies at the 13th, 15th and 16th to reach a momentary tie for the lead before Cook's birdie at 17.

For those like Crenshaw, Lietzke and Nicklaus who hope to come from behind, there's hope to be found in the leaders' track records. All have proved that they can hit the skids when they get near the lead on the last day.

Cook has won only once in four seasons, and that victory (in the Crosby) came when the fourth round was washed out and he didn't have to protect his 54-hole lead.

Clampett, whose only victory is in the Southern Open, blew the '82 British Open when he shot 78-77--155 in the last two rounds when 150 for the final 36 holes would have won outright. And Heafner has never won a tour event.

This gives sustenance to Crenshaw who, after an awful slump in '82 (83rd on the money list), is now back near the top (15th position).

Once, not so long ago, Crenshaw was exactly the same sort of ultrahot prospect that Cook and, particularly, Clampett are right now. However, Crenshaw, 31, now finds himself in his 11th pro season and, despite eight victories, no major titles, no Vardon Trophy, no money-winning title.

"To win here would be my top achievement, no question," Crenshaw said this evening. Almost too softly to hear.