It's not uncommon for people after the age of 35 to drastically alter their entire life. Change the whole act while there's still time. Call it a midlife crisis. What's more unusual is to completely rework the old life from the inside so that you basically seem the same, but feel and act reborn.

Three years ago, John Mahaffey got sick and tired of himself. It wasn't that his life, his work and his personality were so bad. He'd won more than a million dollars on the pro golf tour and his name always would be on the permanent PGA Championship trophy as winner of one of golf's major titles.

But it wasn't how he thought things should or could have turned out. Back in 1970, when he was NCAA champion as a brash, scrawny 130-pound kid from the University of Houston, he usually beat the pants off Tom Watson of Stanford and Tom Kite of Texas. He had more tools, more flair for the game than they did.

Over the next dozen years, however, Watson and Kite just seemed to get better in their plodding way while Mahaffey was inconsistent, injury-prone and a bit self-destructive. Watson and Kite had stable families. Mahaffey got the divorce. They banked the cash. He got the headaches from bad investments. Watson became the king of the sport and Kite won two Vardon Trophies, a money title and was player of the year. Mahaffey was among the top 16 money winners five times -- documenting his talents -- but slumps almost knocked him off the Tour twice.

While Watson and Kite were on the Tour Policy Board, making decisions, Mahaffey still was a bit of a wise guy with the cigarette hanging from his lip and a slightly sardonic view of the whole Tour life.

Some men would be jealous or bitter. Mahaffey decided to take a lesson. "I had a bad attitude."

Three years ago, a friend took Mahaffey aside and asked him if he remembered the night before. Mahaffey said, no, what did I do? The friend told him. Exactly. Nothing terribly bad. But Mahaffey was embarrassed. He looked in the mirror.

Ask Mahaffey now how life looks different from 1983 and he says: "It's not foggy. We're not going to get into that. That's a matter of record."

Cutting the booze before it became a problem was just part of reworking a whole life. For a dozen years, Mahaffey had known his uptight, turf-pounding swing was the cause of his many hand and wrist injuries and that, sooner or later, it would ruin his career. But he couldn't face the work and fear of getting a new swing in mid-career -- not with $100,000 a year coming in.

But that changed. "I had let years go by without getting better. Guys had gone right past me because they had the dedication that I didn't. I realized I better turn my life around, and I did. I admired the Watsons and Kites who didn't have all that much God-given talent but worked so tenaciously and were so competitive . . . I hadn't accomplished the things I wanted to accomplish."

So, at 35, John Mahaffey decided to become an adult. A new swing, a new attitude and a new wife is a bag full of change for a successful man -- a star -- to swallow. But Mahaffey could look in the mirror again.

Slowly, the work paid off. From 56th on the money list in 1982, he climbed to 44th, then 21st, then ninth last season. After winning the Tournament Players Championship here on Sunday, he's No. 1 at the moment. His cash graph went straight up: $77,047, $126,915, $252,548, $341,595 and now $248,500 after just one-third of the 1986 season.

"I have goals now. I never did before," he said. Goals weren't cool.

"I'm not saying what they are," he added, knowing that kids brag, while adults do not. "But I'm not satisfied being right here, right now," he said, the TPC trophy and a $162,000 check in his lap. "I hit some bad shots today. I want to be the best player I can possibly be."

When Mahaffey looks back, he sees the waste, although he doesn't dwell on it. Two U.S. Opens were close to his grasp and escaped. "My record in the major championships has not been what it should be."

For years, Mahaffey resisted the hard, unpleasant realities of his world. The majors do mean more, even though it's not obvious that they should. He did tend to break down under pressure, partly because he didn't think he'd worked hard enough to deserve to win.

The biggest change in Mahaffey, however, is his face. He always could be a nice guy, or a tart and funny one. But he also had the chip on his shoulder that marks the arrested adolescent who desperately wants to stay beyond anyone's judgment -- the cocky kid who never really tries, who never finishes a project, never has the guts to say: "This is no bluff. This is my best."

The perpetual teen-ager in Mahaffey is dead now -- the aging charming wastrel who wonders why things never quite work out for him while lesser men pass him.

His smile comes easier and that old defensive need to lash out at every imagined slight is gone. "I love the life on the Tour and I love to compete," he said at his acceptance speech Sunday. "I'm living the American Dream."

This year's TPC had several pleasant twists in its final act. Pete Dye's gloriously brutal Players Club defended itself well on Saturday and Sunday as its greens baked and the Sawgrass winds awoke. By next March, if new bent grass greens mature properly, Dye's layout may be as slick, scary and yet fair as he dreamed it would someday become.

No tale here was as bracing, however, as Mahaffey's. As he stood over his final, nasty, testing three-foot putt for a one-stroke victory over Larry Mize, Mahaffey said he asked himself for a favor. "Just let yourself do this," he thought.

And he did. In the last three years, you see, John Mahaffey finally has learned how to get out of his own way.