The last man in the last group on the course at Congressional Country Club during the first round of the Kemper Open yesterday was little, and little-known, Gavin (Legs) Levenson of South Africa.

The sun was going down. Gathering storm clouds made the sky so dark that he could not even see his ball in flight. The only crowds left were those on the club's opulently Roman veranda, where a banquet was in progress and a black-tie band played in grand Gatsby style.

Little did anyone know that their leader was approaching.

Well, their coleader.

It had been six hours since anyone had been forced to alter the top of the scoreboard, where fluid-swinging (Dr.) Gil Morgan, at four-under-par 68, stood one shot ahead of down-the-watering-system Calvin Peete.

Morgan, who has always played Congressional well, managed his lead thanks to the friendly mud beside the 18th green, which had grabbed his lake-bound ball and helped him to a final scrambling par in his six-birdie round.

Peete had found an unusual source of his inspiration for his closing blitz of three birdies in the last five holes. On his 14th hole of the day (No. 5), the usually methodical Peete had, carelessly, stood on one foot to avoid putting cleat marks in another player's line while attempting a one-foot tap-in. He missed. What would have infuriated--and ruined--others merely made the embarrassed Peete "more aggressive."

The scores of the glamor players about which many fans cared the most had been computed before lunchtime. Jack Nicklaus, Craig Stadler and Seve Ballesteros ended up comfortably bunched in secure contention, part of a tie for 16th place at 72. Nicklaus even thrilled his massive gallery by lipping out what might have been a hole-in-one at the 166-yard seventh hole; his 6-iron shot trickled over the left edge and stopped five inches directly behind the hole.

This had been a first round with precious little blood drawn. Quality players like Bobby Clampett, Gibby Gilbert and Lon Hinkle at 70 and Andy Bean at 71 were securely in the hunt. Only one curious interloper, Clarence Rose at 70, had managed to climb onto the big top 10 board.

The possibility of bad weather continues today for the rain-plagued PGA, which has already had an entire round washed out by rain in 13 tournaments this year. Yesterday, although gusty winds were tricky all day, although the 7,173-yard Congressional course played long and soft, although the somewhat bumpy greens tended to be of differing and confusing speeds, the day's famous casualties had been few.

True, Johnny Miller shot a 78, then forgot to fill in his score on his final hole and was disqualified; and '80 champ John Mahaffey suffered a 78. Overall, the field of 156 suffered considerably--its stroke average was an almost astronomical 74.98, not counting two disqualifications and a withdrawal. But, by and large, strong players like Scott Hoch (73), Ed Fiori (73), John Cook (73) and Gary Player (74) found ways not to self-destruct.

Thus it was that, almost as a forgotten afterthought, the day's most unusual character--Levenson--walked up the last fairway in near darkness.

As the 5-foot-7, 142-pound Levenson, 28, walked up the par-5 No. 9 (his 18th hole of the day), he thought almost as much about the evening's ambiance as about golf. After all, until he was 25, the titanically long-hitting chap had believed he would always remain "a staunch amateur." But, his game, built on the leg-action that gave him his nickname, simply became too good. Those frequent 300- to 320-yard drives, plus 11 consecutive amateur tournament victories, changed his mind: "I decided I might as well turn pro and see the world while I'm still young."

So, not knowing where his last iron shot had landed, the globe-trotter let his mind wander to the music. " 'Tiny Bubbles,' they were playing," said this tiny bubble on golf's big ocean.

Finally, finding his ball in the back fringe, Levenson pulled out the putter that had "made everything all day" and ran the ball into the hole for a birdie in the gloaming. That tied him with the veteran Morgan at 68 and made him a Tour leader for the first time in his life.

The shy Levenson, who has never finished higher than 22nd on Tour, who missed two months of last season with a golf affliction called "trigger finger," in which the right index finger refuses to bend, had a much harder time this week finding the 400-acre Congressional course than he'd had finding the cup.

Arriving Monday, he and a friend spent three hours being misdirected to the course. "Looking for this place, we saw everything," said Levenson. "The Capitol building, Congress, all of downtown. Seems no one knows where this place is."

Many pros wished they hadn't found Congressional.

Levenson's countryman and buddy, Mark McNulty, came to the 18th hole needing a birdie to tie for the lead at four under; instead he hit woods, water and sand on his way to a triple bogey that put him in a 15-way tie at 72.

Terry Diehl (79) was so mad by the time he got to the 16th tee that he smashed his putter into a cardboard sign, then couldn't get it loose. After a victorious struggle with the sign, Diehl slammed down his club, then, according to partner Gilbert, picked up his bag and body-slammed it to the earth. "Just funny, more than anything," said Gilbert. "Not like Terry, but this place'll get to you . . . This is one course where you do not need the wind swirling around, too. It's like trying to figure out what club to hit at the 12th at Augusta, but it's that way on all 18 holes."

Miller, with a long history of allergies, sneezed his way around in six over, then said, "My putter's allergic to one-putts, that's all . . . This course just doesn't set up for my game."

Even those who survived were hardly chipper.

"I'm never going to do handstands over 72," said Nicklaus. "But it's no problem . . . It could have been a lot worse."

Stadler considered his 72 "very fortunate," since his iron game was "very poor . . . I was hitting everything thin and to the right. With all the wind, indecision set in . . . I changed swings after about seven holes . . . it was a very difficult day, but I made it through."

Only Levenson and Morgan, naturally, walked off exuding the sense that they'd squeezed all the benefit possible from their hard day. Morgan had two bogeys (at the second and 16th) compared to his birdies at the 1st, 5th, 6th, 8th, 12th and 13th. However, he was helped greatly by that mud that kept his six-iron shot at the 18th from what would have been, on a normal dry day, a watery fate.

"After I finished swallowing my heart," said Morgan, with a laugh, "I realized I had a pretty decent lie in the hazard and I hit it to about five feet and made the putt."

Before this week is out, Congressional will make many a pro swallow his heart.