As the sky grew dark Wednesday, one small man dressed all in black stayed on the practice putting green after everyone else had left. He was a rookie on the eve of his first major tournament.

As one putt after another slipped exasperatingly past the hole, the player slapped his hand hard against his thigh and gritted his teeth. Nerves already.

An old fan outside the gallery ropes muttered, "Come on, make one, will ya?", then added, commiserating, "That'll drive a guy crazy."

Finally, the golfer sank a longish one and snapped his fingers happily. "Now that felt good to me," he said. The fan clapped once and actually broke into a gleeful little jog of empathy.

"Soon as I make these, I'll go," murmured the rookie, methodically making three straight six-footers into the heart of the hole. "There," he sighed, confidence restored. Ready to go.

With that, 50-year-old Gary Player, winner of 140 tournaments around the world, a man with career earnings in the millions, ended his last practice session before this week's PGA Senior Championship.

The loyal white-haired fan walked spryly toward the parking lot as though his spirits had been lifted, too.

By Thursday afternoon, after his first round, Player was on the locker room phone calling his family in South Africa. "Would you like to know who's leading?" he said, teasing like a proud little boy. "That's right. Had a 68. Let me tell you, I played a round of golf today."

Player would go on to another 68 Friday for a seven-stroke lead and, at 209, carry a three-shot margin into Sunday's closing round after Lee Elder gained five strokes on Saturday's last five holes.

As he changed spikes, Player beamed.

"I feel like a young man again -- injected with optimism, I'd say. Out here, I'm the youngster. Played with Sam Snead last week -- the man must be the greatest athlete of all time, 74 years old and shooting his age -- and he says to his caddie, 'How come this boy is outdriving me on every hole?' When I was on the regular tour, they all called me 'Mr. Player.' "

Like most famous athletes, Player never thought his sport would still have its hooks deep into him when he was a grandfather. "Twenty years ago at the Masters, when Arnold Palmer, Jack Nicklaus and I were the 'Big Three,' we talked about when we'd retire," Player recalled. "Jack and I said we'd both be gone by 35 -- and glad to be out of it.

"Arnold said, 'I'll play forever, till I can't anymore.' We laughed at him. Now, every year at the Masters, Arnold sees us and says, 'Hey, I thought you guys were going to retire.'

"Now, I know what Arnold meant," said Player, who weighed 150 with a 32-inch waist when he was 25 and now weighs 151 with a 32 1/2-inch waist. "I tell you, this Senior Tour is a bloody joy."

These days, Player and Palmer are discovering (and, come 1990, perhaps Nicklaus will, too) they can actually live out the athlete's most unlikely fantasy.

They can hear the crowds, see their name writ large and win the gaudy prize -- yes, they can play the game, really play it with all their hearts -- forever. It's almost like beating the house.

The saddest sight in sports is a person in his prime, probably not 40 years old, realizing he's already washed up at the work for which he's prepared himself since he was a child. It is only a slight exaggeration to say that a great athlete dies twice and that, of the two deaths, retirement may seem the sharper pain. Housman's poem, "To an Athlete Dying Young," often seems misnamed; in a way, how many world-class athletes don't die young?

All the qualities sport demands and rewards -- love of competition, desire for recognition, dedication to task, ability to perform under stress -- are exactly the traits most wounded and warped by forced early retirement.

Those least suited to cope with an athlete's life are athletes. Yet nowhere, certainly not in any American sport, has any true provision been made so great athletes can continue performing under bona fide competitive conditions before large crowds with millions of dollars at stake.

Nowhere, that is, until the PGA Senior Tour began shocking itself with success the past few years.

"It's unbelievable. If anybody had told me five years ago that I'd be playing a 31-tournament circuit with $7.5 million in prize money, I'd have said they were crazy," said Billy Casper, 54, one of golf's greats. "We're having the time of our lives."

Perhaps the most dramatic, unusual and sentimental success story in sports in the 1980s has been the birth and nurturing of this rich, cheerful and booming golf tour for codgers over 50.

There's a lot of spring in the step of the geriatric set here at the PGA National course these days. Anyone who saw the film "Cocoon" knows how a man feels when the pleasures of youth are unexpectedly restored to him after long years of feeling (to paraphrase Yeats) that old age has been tied to him like a tin can to a dog's tail.

Player is among dozens of well-known golfers, including Palmer, who, once again, have a gallery at their heels and feel the delicious stress of battle. There's also the matter of big bucks, like a $40,000 first prize here.

In his best PGA Tour season, Player won $177,336; this year he expects to double that. After all, Peter Thomson won $386,724 on the 1985 Senior Tour and purses have skyrocketed by 25 percent since then.

It's not just old players who are in heaven. The Senior Tour is producing new stars. Last week, 56-year-old Charles Owens won the first Tour event of his life.

Who's Owens? Oh, nobody unusual. Just a tall, dignified black man, born in a shack by a golf course, who walks with a stiff (fused) leg due to an old paratrooper injury. He has no cartilage in his other knee and, when his incurable eye disease (iritis) flares up, he's almost blind. Naturally, he's the only successful cross-handed player on earth and the only person who uses a 50-inch-tall putter to beat the yips.

Owens, a golf gypsy the last 19 years, also has a two-week-old daughter. "I'm the only Senior player traveling with a baby that's not his grandchild," he said, chuckling.

When Owens won last Sunday up the way at Fort Pierce, Fla., he said, "God gave me my reward. I'm not going to ask for another one." So what happens? Owens had a piece of third place halfway through the $250,000 championship here, the one event that antedates the PGA Senior Tour.

Not surprisingly, Owens has folks in wheelchairs trailing him around the course and others on crutches waiting to shake his hand when he limps off the final green.

In a nation famous for worshiping youth, golfers like Palmer and Owens, Player and Casper, may make gray hair and belt bulge a trend.

"When I'm coming down the last nine holes in contention in a Senior event, I feel just as wrapped up in it as I ever did in any tournament," said Palmer. "My nine wins on the Senior Tour have meant a lot to me. I'll remember 'em a long time."

"I never thought I'd wish for my 50th birthday to come," said Bruce Crampton, twice a Vardon Trophy winner, "but I was counting the days, chomping at the bit. I feel like I've been reborn. I'm having a ball."

Of all the eminent golfers in the last 30 years, perhaps none would have been less likely than Casper and Crampton to use such cheery phrases. Havin' a ball, indeed.

But that's part of the story, too.

"This isn't just a second chance for a career," said Casper. "It's a second chance for some of us to change our personalities . . . Like who? Well, me. I used to be known as a grouch and a grump. Look at me now. Wearing knickers and (argyle) plus fours and silly hats. I never thought I'd see the day.

"But we're out here playing golf with people we've known all our lives. We get to meet some really great fans who appreciate us. We're not faced with a cut this week was an exception . At the end of the week, you're going to get a nice check. If that can't be pretty relaxed and a pretty good time, then there's something wrong with an individual . . . "

For Crampton, perhaps known better for his dour demeanor than his golf, the change has been remarkable. "For some reason, turning 50 has been just a totally different psychological feeling than turning 40," said Crampton, who retired from golf nine years ago and disappeared from the scene until now. "I'm really going to enjoy myself now.

"The atmosphere is so different, not cutthroat, an easier existence. Then, I felt like it was, 'What's this damn Australian doing over here taking our money?' Now, it's 'God, it's good to see you back. We need you.'

"That warmth and respect will bring anyone out (of a shell)."

If the Senior Tour proves anything, it is the almost immeasurable power that the need for competition has over athletes. In retirement, Crampton was a successful independent oil and gas driller in Texas.

"A real masculine occupation," he says. "When you get close to the pay zone, you know you're approaching oil which has been under the surface of the earth for 350 million years. When it comes shooting up out of the ground, it's as big a kick as winning a golf tournament."

Yet Crampton couldn't wait to get out of his drilling boots and back into cleats.

"The further I got away from golf, the more it tormented me," he said. "I'd play occasionally with friends and they'd tell me how great I was hitting it. But I knew different. It was really first-class rubbish, was what it was. It just tended to tease me.

"I tend to be an all-or-nothing person. When I saw how successful the Senior Tour had become, I said, 'Now there's something I can get my teeth stuck into again.' "

That lack of something worthy of sharp teeth is almost a nameless ache.

"It fills in the void," said Palmer, perhaps accidentally meaning even more than he intended. "I've actually gotten to the point where I'm busier than I've ever been in my life, almost too busy." It took a stiff back to keep him out of this week's tournament.

Some Senior satisfactions are more tangible. While the legendary ones, the Palmers, Caspers and Players, get to listen to the cheers of their gallery armies once more, other less familiar tour regulars from the '50s, '60s and '70s are making more money than they ever dreamed. Both Don January and Miller Barber have won more than a million dollars as seniors. Lee Elder, who never even reached the regular PGA Tour until he was 33, has been making up for lost time, banking $307,795 last season.

"Oh, make a few putts one week, miss a few the next," said Elder, chubby and contented these days, playing out of a cart and leading the Senior money list this year. He almost has to pinch himself. He's not the only one.

How fast has the Senior Tour boomed and how high has it risen? A few numbers speak eloquently.

When Player won his first Masters in 1961, the annual purses for the PGA Tour were $1.5 million. This year, the Senior Tour will play for five times that much. In fact, the regular tour didn't get its purses to $7.5 million until 1972.

All this has sprung up so quickly -- almost spontaneously -- that few outside the Senior Tour can grasp it.

In 1978, NBC televised a nostalgia event called The Legends of Golf. Nice, but nothing special. The 1979 Legends of Golf, however, caught lightning in a bottle. Roberto De Vicenzo and Julius Boros won a six-hole playoff in which every extra hole had offsetting birdies. As old-timers sank one long putt after another, and had fun doing it, the idea grew that these guys could still play the game. And entertain.

Pushed by PGA Tour Commissioner Deane Beman, the Senior circuit started gingerly, then exploded. In 1980, there were two events, then five in '81, 11 in '82, 18 in '83, 24 in '84, 28 in '85, 31 in '86 and 37 in '87. Purses rose by an average of $1.5 million a season. Snead and Boros were key drawing cards in the early days, but the real luck was Palmer turning 50 at just the right moment in late '79.

How hot are these old folks?

Their tournaments are in the black before they ever tee up the first ball. The financial backbone of the Seniors -- the brainstorm that has made the whole shebang fly -- is the two-day pro-am.

About 200 amateurs a week pay $1,000 to $4,500 each to play with these old heroes. Three nights of cocktail party socializing are also usually thrown in for the pro-am price. It is a testimony to the warmth and lie-swapping skills of the Seniors that more than three-quarters of their events sell out their pro-ams. The Seniors appreciate and cultivate their amateur partners, knowing they pay the freight.

For instance, Doug Sanders' group completed its pro-am round almost in the dark this week, yet (with only three spectators still in the grandstand), Sanders took an interest in each of the hackers' final putts, then headed for the 19th hole with them.

Companies can't line up fast enough to sponsor events. "We have 35 corporate sponsors waiting to start new events," said tour official Ric Clarson. "In '87, we'll have six new tournaments."

Despite the Seniors success, the old folks circuit is still something of a secret. Only one Senior event is carried on network television (The Legends), although eight tournaments are on cable TV with ESPN.

Interestingly, gate attendance isn't as important economically as pro-am fees or corporate sponsorship. Still, some Senior final rounds draw more than 10,000 people. A typical event might have 5,000 for the finale and 15,000 for the week with $7-to-$12 tickets.

In fact, the Senior Tour has come on so strong and so fast in the last two years it has acquired the surest mark of rapid success. Controversy.

Anybody who's watched senior citizens play canasta knows that the older you get the more you argue about the rules. It's that way on the Senior Tour. The first casualty: Bob Toski, one of the game's most famous teachers. Early this season, Toski voluntarily withdrew from competition after fellow players claimed he had been moving his ball on the greens to avoid spike marks.

"I don't think Bob Toski did anything purposely wrong," said Palmer, stating the Senior consensus. "He was just a little careless. We're sorry it ever got out. On the other hand, we have to emphasize that we're the only game where you call penalties on yourself."

"Let's just say that the players had a meeting recently to remind each other that integrity was essential to the game," said Senior Tour spokesman Clarson. "Hey, nobody did anything really bad -- no leather mashies (shoes) in the rough."

The best player in the brief history of the Senior Tour has been Don January, the first man to win a million dollars in the December stage of his career. He's a tough Texan who likes to say, "I do it for the money, plain and simple. It keeps me going. I still owe the bank money . . . "

On Friday here, January played despite having the flu. After his round, he collapsed in the locker room and had to be rushed to a hospital emergency room. As January, on a stretcher receiving oxygen, was being wheeled out of the locker room, a worried Billy Casper looked at him and said, "It reminds you that this really is the Senior Tour."

Age, however, changes little in an athlete's heart. He looks different on the outside, but inside, everything feels so much the same.

Within a hour of being released from the hospital, January was on the phone assuring people at tournament headquarters that he was "perfect."

Would he play in Saturday's round?

"You bet," said January. "I may ride, though."

Why would a sick 56-year-old who is 14 shots out of the lead want to aggravate himself with two more rounds of pressurized competitive golf? After all, he couldn't really win, could he?

"Well," said January, "they pay more than one, don't they?" CAPTION: Picture, Don January, PGA Senior Tour's first $1 million winner. UPI