Athletes, by definition, do not age well. The desire is there long after the flesh is unwilling.

Willie Mays, at 42, was a forlorn figure in the batter's box and we pitied him. Billie Jean King, perennial quarterfinalist at 36, is revered by those who could not abide her in victory 10 years ago. And Muhammad Ali, at 38, seems silly shadow boxing with a vision of his former self. Worse, we worry about his health.

Last January, Jack Nicklaus turned 40. "My kids wore 'Jack Nicklaus is 40' T-shirts to the birthday party," he said. "I wouldn't wear one of those things. In fact, I'd like to burn them all."

The Golden Bear had been in hibernation for almost two years and many, himself included, wondered if the legend had been put to sleep for good. He had not won a golf tournament since July 1978; nor a major one since 1975.

"Did I have any doubts?" asked his caddie, Angelo Argea. "It's hard to say, I just kept hoping he'd wake up sooner or later."

Nicklaus began to stir in March, finishing second to Ray Floyd in a playoff at Doral.

Then, this summer, he went on the prowl, winning his fourth U.S. Open in June, and his fifth PGA two months later -- his 18th and 19th major titles.

Nicklaus is the man who once said, "It is a project for me to smile." But as he stood on the 17th green at Baltusrol, his PGA title and his sense of himself intact, a sweet smile spread from the crow's feet on down.

The expectant throng waited for some words that would measure up to what they had just seen. But, Nicklaus said, "I just didn't have anything to say. I think the people understood."

Even now, it is difficult for him to articulate just how good he felt.

"What is meant to me, inside, coming back . . . All those people who had been giving me static, all the problems my wife had to put up with, all the people telling my kids, 'Your father is washed up.' I suppose all that was wrapped up in that smile."

And people who think that golfers are just a bunch of Republicans dressed up in plaid polyester, smiled with him. Because Jack Nicklaus had shown that it is possible for an athlete to age well.

He considered the idea for just an instant. "You have to," is all he said.

Following the final round at Baltusrol, after the last hat had been signed and the last question pondered, the big dog, as Lee Trevino has called him, went out and had a Big Mac. "That's where Michael, our youngest son wanted to go," said Barbara Nicklaus.

"After the PGA, we didn't even get to McDonald's," added her husband.

How much more can the big dog eat?

"As much as he wants," said Trevino.

It depends on his appetite.

Trevino was asked if he had ever seen Nicklaus more excited than he was after the Open? "You know, I don't sleep with him," he said.

But, Trevino admitted that he had never seen Nicklaus as ravenous for a title as he was at the Open. "He wanted it and he wanted it badly," he said. "I like to say if Jack tells you an ant can pull a bale of hay, then you better find a harness and hitch him up. If he wants something bad enough, he'll get it."

Nicklaus may just be named player of the year for 1980. "How important is that? For 1980?" he said. "Very. We'll only have one this year."

Or, perhaps, they'll give him the award for "most improved player." "I'll probably get that," he said, "or the comeback award or maybe just most-likely-to-succeed."

After all, as the guy at the ninth green said, "Who does he think he is? Jack Nicklaus?"

Jack Nicklaus believes that Ali will win the heavyweight championship again in October. "If he gets in shape, yes, I think he'll win. I hope he wins. But I hate to see him in the condition he's in now. Last summer, in Germany, I ran into Max Schmeling and Max said it was embarrassing, that Ali was 280-285 pounds. There's no way I'd let myself go out and do that kind of thing."

Yes, he sees the analogies. The question with Ali, he says, "is whether he has let himself get beyond the point where he can get back to the position where he was before."

Physically, that never happened to Nicklaus. The man who was labeled "Ohio Fats" and "Beef Boy" early in his career would never let that happen. "I can't stand the way I am at the end of the golf season," he said, patting his stomach.

But mentally, he felt it coming. He was approaching the point emotionally where it was going to be impossible to return "from that far back."

And did he say to himself, "Not yet?" he was asked.

"Exactly," he said.

"Golf is a funny sport," he said. "Many have done better physically right round the age of 40 -- Hogan. Snead, Boros. What usually happens is that the nerves end up going. Even with Palmer. Physically, he's been all right but the rest of the game has not been there. That's been his problem, and that's been my problem, too.

"If I had not gone through a bad stretch, the wins at the U.S. Open and the PGA would have simply been the natural extension of my career. But I did go through a bad stretch and the basic question was: is it a bad stretch or a decline in ability? In my opinion, it was just a bad period, primarily due to my putting and my short game. It was an accumulation of three or four or five years. You begin to kid yourself a little bit."

Nicklaus has said that in golf, "Your frame of reference must be exactly the width of the cup, not the general vicinity." But his frame of reference had become his burgeoning businesses, his growing family.

Two years ago, when he cut back on his golf schedule, he said, "9,000 people second-quessed me." He became the 9,001st when, last year, for the first time since 1962, he did not win a tournament. Now he says he knows the schedule can work.

"What was your body doing last year," a man asked Barbara Nicklaus as she followed her husband's progress on the first day of the World Series of Golf.

"Loafing," she replied.

He would spend perhaps two days, she said, preparing for a major tournament, pretending it was enough.

But, "you know," she continued, "everyone said what a bad year Jack had in 1979 but in other ways it was a great year. We saw our two oldest boys play in the state football championships and our daughter go to the sectionals in volleyball."

In December 1978, Nicklaus flew home between rounds of a tournament to see his sons play in the Florida state football championships, a friend recalled.

Nicklaus gave up football after junior high school. One day, he said, "Woody Hayes came into my dad's drugstore and my father asked him whether I should continue to play football. Woody said, 'With the talent he's got, I'd keep him out.'

"My dad played pro football for the Portsmouth Spartans and he loved the game. He was crushed but he never told me that."

Nicklaus gave up many things, including much of his childhood, according to an old friend, Kaye Kessler, a writer for the Columbus Citizen Journal. "He never had a chance to be a kid. I wrote a magazine piece about him when he was 13. He had on this straw hat like Sam Snead's and the headline said, 'Move Over Sam'"

Whatever experience of his own he may have missed, Nicklaus was determined not to miss those of his children. While he played with his kids, the kids on the tour outplayed him. He was, as always, a gracious loser -- the "best loser," Gary Player once said. "My Dad told me. 'You don't have to like losing but be sure you fake it,'" Nicklaus said.

But you can't fake it for a year and a half.

"One year of it was enough," Barbara Nicklas said. "He wouldn't have stood for another year."

So he went back to work. "Instead of going to the office first, he went to the golf course and then the office," said his wife.

"He went back to six, eight, nine hours a day of hitting golf balls," Trevino said. "I wasn't working to win," Nicklaus said "I was living on what I had."

"Ever since I was a boy, I was always trying to learn something," he said. "When I tried to evaluate 1979, I realized I didn't learn anything. The only thing I did learn was that I had to change my game if I wanted to maintain it. So in 1980, I revamped parts of my game . . . . Try to imagine after 25-30 years, making a total change in your short game, changing your swing plane. Those are drastic changes. I didn't know if I had the ability to do it."

With the aid of Phil Rogers, he retooled the short game -- particularly his wedge shot -- he had neglected for so long. "People would go up to Jack Grout (his old teacher) and say, 'why in the world would you let Jack do that.' And he'd say, 'Let him alone, he's going to make it work.' Now I'm getting lots of letters saying, 'Send your crow, broiled or fried, or however you want it'."

On the ninth hole of the first round of the World Series of Golf, Nicklaus hit a 50-yard sand wedge for a birdie, his best shot of the day. "It felt so easy, I didn't know I did it," he said."The ones on four and 16 weren't bad, either."

Nicklaus had saved par on the fourth hole with another pitch. "Trevino told me, 'I told people that crazy little method of yours would work. You stuck with it, you believed in it, and you made it happen.' You have to have patience in this game."

He worked with Grout on his putting. But it was not until just before the PGA, when his son, Jackie, notice that his father was not going all the way through the ball, that things fell in place. "Suddenly, putts were going where I was looking, some will finally go in and then you start to believe."

But it was six months before all of Nicklaus' work began to pay off. And, yes, there were moments when he wondered if it was just gone for good.

"We all go through that," he said. "When I turned pro, I didn't win a tournament until my 17th. I said, 'Am I ever going to win? Is my ability as an amateur going to work as a pro?' In 1967, I had a long spell without a major and I said, 'Am I ever going to win another major?' I've gone through four or five periods like that. They started writing me off in 1968 and 1969."

Certainly, that appeared to be the case at the 1980 Masters. With both Nicklaus and Palmer out of contention, the organizers paired the old rivals together for the last round, a cruel reminder of what once might have been. As the two men trudged up the last fairway together, the implication seemed clear.

Nicklaus was being stuffed and mounted and put behind glass, right beside the man he helped to put there. "God, I hated that tournament," he said, "and that's what I hated about it."

But, Nicklaus wasn't ready to become a "ceremonial" golfer, the way, he says, Billie Jean King hs become a "ceremonial" tennis player. "She had won everything there was to win," he said. "She took a year off and now people don't take her as a serious No. 1 competitor. There will be a time when I'm not a serious No. 1 competitor. I will go from a competitive golfer to a "ceremonial" one someday in the not-so-distant future; two, five, maybe seven years from now.Hopefully not next year.

"Then I will be that in my own mind. I won't be out there to compete but to contribute to the game. To go some places I haven't been.

Nicklaus, of course, has been here at Firestone before. He has won seven tournaments on this course, a home away from home for one of Ohio's favorite sons.

America is on a first-name basis with Nicklaus (an honor accorded only the rarest athletes: The Babe, Arnie, Billie Jean, Jack). But here they feel they are entitled.

The day of the first round, Nicklaus was paired with Tom Watson and Lee Trevino, a television producer's dream. A slight to the other competitors, Nicklaus said.

On the 12th tee, Watson spotted a man in the crowd with a USC T-shirt. "No Rose Bowl for you this year," said Watson, a Stanford graduate. Then, looking over at Nicklaus, he said, "It's gonna be Stanford and Purdue."

Immediately, the crowd started humming the Ohio State fight song, in honor of their favorite Buckeye. Nicklaus smiled.

Later, Wilson was asked how he liked golf's version of the menage a trois. "It was fun," he said. "It reminded me of the old days, when Nicklaus, Palmer and Player used to play together. When was that, Jack? The late '40s?"

"No, it must have been the '30s," Nicklaus replied.

In June, at the Open, Watson said publicly that perhaps Nicklaus would retire if he won. Nicklaus didn't take too kindly to the suggestion. "I just didn't think it should come from him," Nicklaus said. "Tom's a nice guy. He's kind of the same position I was with Palmer. I can understand, having been on both sides."

Nicklaus knows that one day, not too long from now, he is going "to reach down and it's not going to be there." This summer will make that time easier, he said. "If I had any common sense, I'd say goodbye right now."

But what's the hurry.As he approached the first tee the other day, a boy stepped in his path. The back of his T-shirt had been autographed by everyone but Nicklaus. The boy bent over and Nicklaus signed. The boy turned around to say thanks.

The shirt said: "Jack Is Back."