The two fundamental approaches to golf came to the fore in PGA Championship today -- technique and mystique.

Tom Watson, that master of drudgery who oozes character, shot a fourunder-par 66 on Oakland Hills, while carefree comic Rex Caldwell, who is a character, somehow managed 67.

A starling total of 15 players broke par here today as the hallowed Hills played its easiest ever, thanks to feeble rough and a week of rains that left the 7,014 yards of the renowned monster playing both soft and slow.

In five previous major tournaments here, only 49 rounds had been shot under par. The 21 rounds in the 60s during the 1972 PGA were the most in one event.

"Oakland hhills was as much a piec of cake today as you'll ever get it," said a disgusted Jack Nicklaus, who finished bogey, double-bogey for a far-back 73. "I didn't even get to the icing."

Event those who fasted on Oakland Hills during this balmy day have to wonder if the ecstatic Watson will not use this showcase to reestablish hisgolfing supremacy. Ron Streck and Jay Haas with their 68s may have no more change for victory than Tom Weiskopf with his 79 or Arnold Palmer with his 81.

The logjam at 69 with 11 players, including past U.S. Open champs Lou Graham, Hubert Green and Jerry Pate, and those other gents at 70, including Lee Travino and Dave Stockton, normally would consider themselves in prime striking position. But it might take Sherlock Holmes to apprnhend today's revitalized Watson.

As soon as Watson stepped to Oakland Hill's first hole today, playing partner John Mahaffey, the defending PGA champ, could sense from Watson's bearing that the two-time player of the year has finally solved the swing miseries that have humbled him the last two months.

"You got it figured out, huh?" asked long-time friend Mahaffey, who had watched Watson hit everything sideways, fuming and fussing the while, throughout their two practice rounds this week.

"Yeah, I got it figured out," said golf's premier theoretician, explaning an esoteric practice-range discovery made just the night before, "I wasn't establishing my left-arm radius for full extension."

To most folks, even those behind the gallery ropes on this rolling course, that means nothing. To this PGA, it means the whole shebang here may be over already. Watson is in a state of barely concealed, full-scale psyche.

"I'm excited again about the game, really excited," said the grinning Watson, who, after missing the cut in the U.S. Open in June has been deep in the doldrums despite a record $387,386 money-winning season. "It only takes one instant to turn it back around.

"You can find the key swingthrought in a dream or sitting down at breakfast -- anywhere.

"The golf swing is something that just slips away. You can't repeat it forever. It's a fleeting thing. You grab onto it and hold on as long as you can.

"When you lose it like I did, it can feel like drudgery as you keep fighting it, fighting it, every day trying something new until you get it back. Then, all of a sudden, the sky is blue and it's fun again.

"It came to me on the fourth tee yesterday, a thought I used to use but had gotton away from. I'm an armswinger, not a leg man. When my arms get out of rhythm with my body, things start to go haywire left and right."

Now, by concentrating on his square arm extension away from and through the ball, the game is child's play once more. Watson's round was simple: He tore the guts out of Oakland Hills' narrow fairway, peppered the pins with close irons, birdied both par 5s and three of the 4s, and would have had 65 if he hadn't buried a bunker shot at the 18th.

"I just love this course. It's one of the very best -- a true northern course with those big undulating greens where your have to place the ball on the proper side of the dead elephants they've got buried. Oakland Hills will get tougher each day as it dries out. This was the day for scores. This course is much tougher than the scores. It's going to get harder."

Among the distinguished who were ricking themselves on this day when anything over par was a blow to chances of victory were Gary Player and Hale Irwin with 73, Ray Floyd (who shot 63 in a practice round Wednesday) at 74, and Andy Bean with 76. Lee Elder had 70, despite five birdies, and ruld missed opportunity, George Burns, once four under par, and Jim Thorpe shot 71.

At the glorious opposite extreme from Watson's self-contained perfectionism was the totally relaxed humor of Caldwell, a reformed tour playboy known for years as Sexy Rexy, who has now become known as "Drain-O" -- the man who sinks everything.

Many a nobody has led a major golf tournament for a few hours, as Caldwell did today, but few have admitted their anonymity or enjoyed it so much.

"Sure, I'm nobody," said the 29 year-old who, after three years of tour scuffling, made it to the exempt list in 42nd placed last season. "Nobody knowns who I am, In fact, last Wednesday I shaved my mustache after having it for eight years and now when I look in the mirror event I don't know who I am."

Although there is only one Watson, there are many on tour who emulate his technical approach to the game. Two hands could count those like Caldwell, the best buddy of free-spirit Fuzzy Zoeller, who are determined to savor every minute in a lush golf world they never through they'd crash.

Caldwell, who never played amateur golf ("because I had to pick up range balls at night just to make money for the greens fees the next morning"), never has had a lesson, and never broke par until after college, is the glory of the common man. Let him describe, in his marvelous free-form way, what it feels like to hit just one shot in the PGA.

"I thought about hitting a big sling hook with a two-iron at the ninth hole," explained Caldwell, a 6-foot-2, blow-dry disco darling. "But I sure didn't want to pull out the three-wood. But, finally, I reached in there and pulled out the furniture (three-wood) anyway.

"I hit me a streamliner, a real hot firecracker about two-and-a-quarter (225 yards) uphill and into the wind. The pin was in the coffin corner, but I had it turning right down the stack, I was hot and running . . . through I had me a 'one' (hole-in-hole). That ball just blacked out the stick.

"I still don't know how it backed up into the bunker for a bogey."

To Caldwell, currently 47th in winnings, golf is more magic than mystery, more grit than technique, "I don't have as good a golf game as most of these guys, but I have a lot more guts," he says, "You can will the ball into the hole . . . don't tell me you can't. I did i all last year. I made everything I looked at for an entire season. That's the only way I get exempt, cause I sure couldn't hit it worth a dern.

"When I cane on tour in '75, I was one of those guys that you just knew would be there in '76. It came down to the last putt of the last tournament of the year -- a four-footer -- for me to keep my playing card. I made the ($3,000) cutoff by $91. If I'd missed that putt, I'd probably be punching buttons in a supermarket.

"Every time Arnold Palmer sees my swing, he says, Rex boy, when are your going to get a real job?'"

Despite his beer-in-hand devil-may-care gab, Caldwell has a serious streak. He has refused to attempt to qualify for the U.S. Open because he thinks it is a "disgrace" that the Top 60 aren't automatically exempt. And in the only other major tournament of his life he realized on the morning of the forth round of the PGA that he has signed an improper score the previous day. He immediately disqualified himself, although no one would ever have suspected he was one shot too low.

"I could never have lived with myself if I'd known I had cheated," he says, "even if it was the difference between an 80 and an 81.

"That'll never happen to me again," he vows. "You should have seen my scorecard today with that 67. It had check marks all over it, I had three different people add it up."

No matter how you tabulate this first round at Oakland Hills, the sum is the same: One hot and happy Watson may add up to more than the other 149 fellows here combined. CAPTION: Picture, Tom Watson coaxes putt en route to PGA-leading 66. AP