At the highest levels of sport, every game becomes a mystery even to those who play it best.

Particularly in golf, the differences in performances from week to week, and year to year, are so small--yet their consequences are so great--that even the athletes begin to doubt that they know the true sources of their excellence or the variables that act on their careers.

Perhaps no golfer has been better at analyzing the twists and kinks of his own game and personality than Jack Nicklaus. And, it could be argued, few golfers, if any, have been worse at managing their own careers, or have seemed more at the mercy of forces they didn't quite understand, than Johnny Miller.

This afternoon, Miller and Nicklaus, golf's two conspicuous blonds, rose to the top of the leader board at the Honda-Inverrary Classic--both struggling to work their way back up through the tormenting levels of their game.

Miller was the winner this day, his 69 for a 10-under-par 278 total earning him $72,000 and a two-shot victory over the man he says he takes more pleasure in beating than anyone else: "Mr. Nicklaus."

The Golden Bear, who started the day in 30th place, played the last 12 holes seven under par and finished with 66--280 for $43,200. "I could have birdied the last six holes in a row," he said, but three of those putts stayed above ground. "I haven't really had a good round this year . . . This has been my brightest spot for a while."

For Miller, who ended a four-year slump with a victory here in 1980, this was another arduous "step back up the ladder" toward the pinnacle he attained in 1974 and early 1975 when he seemed on the verge of redefining the game's possibilities.

"I don't know if I'll ever do that again . . . that was sort of crazy golf. I don't know if I even want to," said Miller of those now unimaginable days when he shot 63s and 61s. "With a couple of more steps, I can take a shot at being one of the best again. Maybe not the best, but the top two or three."

That climb up the ladder, either the first time when the body is young and the goals vivid, or later, when the nerves protest and the taste of victory hardly seems worth the aggravation, is at the heart of every golf season. March in Florida is the month when we see who is going up, who down. For Miller, 35, and Nicklaus, 43, the direction, once more, may be toward the top.

This afternoon, Nicklaus admitted that, between Tom Watson's historic chip-in at the U.S. Open last year and today, he hadn't done anything of golfing significance. "That shot, after as hard as I'd played, and thinking I'd probably won the tournament, was enough to blow my desire for the rest of the year. I kept trying, but nothing happened . . . You have to be man enough to come back from things like that. But sometimes it takes some time."

This spring, playing more spring tournaments than he has in years, Nicklaus has begun to see the beginnings of "the tournament toughness . . . the mental toughness . . . that you need to shoot good scores."

Nicklaus has always been able to make just such fine-tuning, appraise the impact of events on himself and react with a logical program. For Miller, it's been far harder. After three years in oblivion from '77 through '79, when he was 48th, 111th and 76th on the money list, Miller has returned to modest success the past three years, finishing 30th, 12th and 20th on that list.

Now, he can daydream again.

"With that next step (up) my game would be ready for the majors. I might be a year away. Right now, if my nerves would hold up, I maybe could do it," said Miller. Then he added, "That is, if I could convince myself it's the Tallahassee Open instead of the Masters."

Miller hardly needed nerve today as his battle with Nicklaus had little drama. Nicklaus went out early and, as he has done so often in his career, played his best when he had nothing to lose.

By the time Miller, who started the day in third place, had made the turn in two under par, he had taken the lead alone at nine under par; Nicklaus had finished by the time Miller played the 13th hole. Miller's only misstep, a bogey at the 13th, was quickly remedied by a birdie at the downwind par-five 15th.

Nicklaus, watching on TV as Miller nudged his lead back to two strokes, said, "It's history . . . Johnny'd have to faint."

Had he, Nicklaus, ever fainted?

"When our first child, Jack, was born, they pointed to him and said, 'That one is yours.' I keeled over backwards," said Nicklaus. "I'd never fainted before. When Steve was born, same thing. Passed out again. I was in the recovery room longer than Barbara. The third time, with Nan, somebody caught me as I fell. The fourth time, for Gary, I brought my own smelling salts, but I fainted again. The last time, with Michael, everybody was ready for me (to faint again), but nothing happened. I told Barb, 'That's it. No more kids.' "