Ed Sneed's golfing war with himself has always been the same: strong mind, recalcitrant body.

For more than a decade, the 34-year-old Sneed-compulsive student of analytical games, reader of books, less than gifted natural athlete-has tried to beat the game of pro golf with his brain.

As is common is such cases, the pitiless sport usually has won.

Today, a supremely confident, utterly controlled Sneed, playing in a precariously maintained concentration, had his reward. His clean, unruffled round of 69 gave him a stunning five-shot lead after three rounds of the Masters with a gaudy dozen-under-par total of 204.

Golf's current king, Tom Watson, and Craig Stadler stood in second place at 209, with Bruce Lietzke and Fuzzy Zoeller just a shot behind them. Yet all four conceded what would have seemed incredible three days ago-that Sneed, who never has won a major title, or finished higher than 27th in money winnings, has a green jacket in his hands.

This 43rd Masters is his to win or squander.

In fact, after his almost errorless afternoons of 68-67-69, Sneed can become the first man to shoot four sub-70 rounds in the Masters.

When a pro athlete, who has labored for 11 years without once catching the nation's attention, suddenly discovers a few days of genuine greatness, there often is some single moment that illustrates his abrupt emergence into a temporary state of grace.

So it was today for Sneed at the Amen Corner.

As he strolled down the 11th fairway, holding a three-shot lead, Sneed twirled his driver in his fingers like a toy baton.

By the time Sneed reached the 12th hole-the 155-yard devil that has undone more Masters pretenders than any other-he was in a condition of almost syrupy nonchalance.Sneed was swinging like Snead.

And why shouldn't he be? He avoided a bogey for the first 40 holes of this tournament. His every shot, even with hiss woods, looked like an effortless three-quarter wedge.

"I've never seen anyone in my life play like Sneed is right now," said Zoeller. "Everything he hits starts on the stick and never leaves it. He has a birdie putt inside 15 feet on almost everyhole."

At the 12th tee, Sneed chose a six-iron. He might as well have pulled a kingly scepter from his bag. The shot he was about to hit probably will be looked back upon as the one that did the most to ennoble him with golf's regal green coat.

Sneed's towering iron shot arched high over Raehs Creek, still muddy and turbulent from Friday's storms, and bored its way through the day's steady breezes. The ball plummeted to hit within a foot of the cup, barely missing a hole in one before biting and stopping just a yard from the hole. The dead-level tap-in was a formality.

Predictably, the charged-up Sneed birdied the easy par-5 13th to go 12 under par, then parred his way steadily and conservatively into the club-house with a mammoth margin for Easter Sunday error.

For the record, the Master's best-score is 271, its largest margin of victory nine shots.

Of all pros, Sneed seems among the least likely to ever spend a night dreaming of such possibilities.

Sneed was a nondescript high school golfer, shooting in the 80s. He was unable to crack the Ohio State freshmen basketball team.

Even his collegiate golf career left little mark. Among OSU's trio of tour pros-Jack Nicklaus, Tom Weiskipf and Sneed-the latter's claim to distinction is that he is the only one to earn a degree.

Most young pros arrive on tour with the ambition of reaching the top-60 exempt list immediately. It took Sneed five long scrimping years just to crack the top 100. Even as recently as 1977. Sneed dropped out of the elite 60. His current 19th-place standing, with $52,189, is by far his loftiest perch.

"At other times in my career, my tempo has deserted me," Sneed said after his round. "I get hurried, I've felt a lot more nervous on golf courses than I have since I got into this Master's lead."

Blind confidence, it's wonderful.

Every golfer, at almost any level, knows the feeling of suddenly finding a rhythm and groove when the game seems elementary.

Pro golfers are the first to know the true drift of a tournament. They understand and watch for those ebbs and flows of confidence, those birdie streaks endemic to the game.

For just that reason, the pack of hounds on Sneed's track fears that the trail already is cold.

"The only change I have to win this golf tournament," said Watson "is if I play exceptionally well, a lot better than I did today, and Ed Sneed doesn't play well."

At the moment, Watson has misplaced the groove that he was in as recently as Friday afternoon before the deluge.

"I haven't gotten my motor started since," he said. "Also, I hit a lady in the mouth with a drive today at the 10th and it really shook me up. She had a couple of stitches and is okay, but that never happened to me before."

The rotund Stadler, by contrast, played as though he were the one who had just been conked with a drive. Starting the day tied with Sneed, three shots ahead of the field, Stadler sank like the world's fastest submarine. At the 11th he plunked his approach in the pond and proceeded to double bogey-the central blunder in his 74.

"My changes sure aren't as good as they were before today started," said the cheery, red-cheeked Stadler, termed by males in the gallery as "that well-constructed man" and by females as "that blimp."

The man who has only himself to blame that he is not much closer to Sneed is Bruce Lietzke, whose 67-75-68-210 has mirrored the erratic behavior of the weather. "I seem to have convined myself that I'm a fair-weather player," said the self-critical Lietzke, "so now I'll probably never be able to play in bad weather."

While others were almost conceding this title to the waltzing Sneed, Nicklaus was an almost-comic figure in maintaining that he-tied for 11th at 212-still had a change.

"I'm only three shots out of second place," day-dreamed the Bear. "I feel like I played well today but nothing happened."

Been a lot of that lately, Jack? Arnold Palmer has been saying the same thing since he turned 39.

As might be expected, the dayhs forgotten mans was Mr. X, Miller Barber, golfhs anonymous millionaire. In the morning, he completed Friday's suspended round, finishing par-birdie-par to tie the course record of 64. His incredible 11 3s were three more treys than anybody had ever had. Barber's round even included a bogey 6. On his one eagle of the round, Barber never saw his ball disappear in the hole since he refuses to remove the ever-present sunglasses that are part of his CIA facelessness. Naturally, he finished his afternoon 72 with a bogey-bogey that neatly pushed him out of preeminence.

Sneed, almost as much a master of invisibility as Mr. X, perhaps he is Mr. Y, is a popular leader among his fellow pros. As the player-director of the tournament policy board, Sneed has the reputation for doing the dirty work that other pros avoid.

Sneed's other reputation is one that is unique to sports. "Too smart to win a major," is the longtime locker-room tag.

A certain natural athletic unconsciousness is seen among pros as a prerequisite to those strings of birdies that lead to fortune.

"Heck, Ed's a real smart guy," said Hubert Green. "The rest of us are just golf pros."

"Ed'll say things that you have to stop and think about," Ben Crenshaw siad with a grin.

With his meticulous manner and subdued smile, Sneed is a natural student-a lover of intricate games like chess, bridge, billiards and backgammon. He is also such a purist about analyzing the golf swing that he virtually refuses to discuss his own, saying that "what I say would seem utterly meaningless to the average person . . . and it would only get garbled in the retelling . . . I don't want people saying, 'That darn Ed Sneed doeesn't know what he's talking about.'"

When Sneed is not being a sort of PGA model citizen, he was a wry sly wit. He can mimic Gary Player's famous self-congratulatory interviews until the locker room is a shambles of sardonic laughter, and he can do a first-rate immitation of Arnold Palmer's slashing swing-but going backward like a crazed movie camera in reverse.

When he steps to the first tee of Augusta National On easter Sunday morning, Ed Sneed, after 21 years of struggle with the game of golf, will finally resemble that hero of his youth-Palmer.

Only this time the resemblance will not he in reverse. Sneed may at last join the Sneeds and Palmers of his dreams. CAPTION: Picture 1, Ed Sneed follows ball as he tries for short putt on the seventh hole during third-round play. AP; Picture 2, Tom Watsonhs caddy supplies the body English to encourage putt toward the 10th hole at AUGUSTA. One of Watson's approach shots coming into 10th hole struck a woman in the gallery in the mouth. UPI; Picture 3, Craig Stadler, tied for the Masters lead after two rounds, blasts out of trap on seventh hole. He shot 74, good for a second-place tie with Tom Watson at 209 going into final 18 holes. UPI