George Burns, who three weeks ago thought he might never make another cut, is leading the U.S. Open. David Graham, who hadn't played for a month because of a potassium deficiency, is one shot back. And Jack Nicklaus and Tom Watson, Golf's goliaths, are lurking close behind, both men supremely confident.

After 36 holes, the 81st edition of this premier golf tournament is just beginning.

Today, some of the imposters began to fade. First-day leader Jim Thorpe went from 66 Thursday to 73, which was a lot better than J.C. Snead, who went from 67 to 77, and a good deal better than club pro Bob Ackerman, who followed 68 with 78.

It was not until almost 8 o'clock, with dusk fast closing on the Merion Golf Club, that the leader emerged. To the surprise everyone, most notably himself, it was Burns, 31, a former University of Maryland player. Burns shot 66 today, getting his birdies early, then picking his way through the treacherous closing holes without any of her troubles that befell many others. That put him at five-underpar 135, one shot ahead of Graham, the resolute Australian who also had it five under until he missed a four-foot putt at 17. Graham shot 68 for 136.

One shot behind Graham come Nicklaus and Tommy Valentine.Valentine shot a solid 68, making only one bogey. Nicklaus almost had one of those Nicklaus rounds that leaves his opponents gasping. He was five under for the tournament before No. 16 jumped up and grabbed him for a double bogey, the only hole he did not reach in regulation.

Four players are at 138. John Cook, who shot a 70, making his first bogey of the tournament at 18; Greg Norman, the shark-hunting Australian who had 67; Bill Rogers, who was four under until a double bogey at 18, and Bill Kratzert, who birdied the fourth, then made 15 straight pars for a 69.

But it is one shot further back, at 139, that all the leaders are looking. There are seven players there, including 1976 champion Jerry Pate, Lanny Wadkins and Jack Renner. And Watson.

Like Nicklaus, Watson threatened to tear up the course. For 13 holes he was keeping the ball in the fairway off the tee and looking at birdie putts each hole.

He was three under when an amateur photographer snapped his shutter while Watson was at the top of his back swing on the 14th tee. The ball ended up in the rough. Angrily, Watson suggested the photographer either learn better timing or not take pictures on a golf course.

"I was," he said, "very firm with him."

The bad tee shot led to a bogey and Watson finished with 69. But he was smiling. "I'm playing well," he said. I'm excited about my chances to win."

From Watson, that is almost a warning. Generally, he finds many faults with his game and his swing. The same can be said of Nicklaus, who said simply, "I played about as good as I can play except for one swing today."

That swing came at the 16th. Nicklaus had missed his drive and was about five yards into the rough on the left side of the fairway. He had 185 yards to the flag and arrived at his ball to find it sitting up.

"It was a much better lie than I expected," he said. "Usually you go in the rough here it's a pitching wedge to get out. I played a four-iron. I wasn't sure if the ball was going to fly so I tried to pick it (hit the ball without taking a divot). I got too cute."

He hit way wide, the ball landing beneath a tree, and, after chipping out, he hit a weak sand wedge short of the green. He finally got on in five and "saved" his 6 with an eight-foot putt.

That kept Nicklaus from sharing the lead with Burns. Always a money winner, Burns grabbed a title for the first time last year and made $219,928 to finish seventh on the money list. But this year his best finish has been a tie for fourth at San Diego and he is 42nd with $55,015 in earnings.

He never before has played well in an Open, his best finish a tie for 27th last year. He did not come here thinking victory.

"I have a tendency to be wild with my driver and when you do that in the Open it usually costs you two shots instead of one," he said. "The key for me is that I've avoided disaster the last two days. I haven't had any of those 7s or 8s that pop up."

He has also made 13 birdies, the new putter apparently doing wonders. Burns' strengths last year were his driver and his putter. But be broke the shaft on his driver in England last fall and, nine new shafts later, gave up on it at Westchester. He also had his putter regripped -- to his dissatisfaction. He changed at Westchester.

Today, the putter had it easy. Burns pitched to within five feet for a birdie at No. 2. Then at the fifth, with his drive in the right rough, he flew a seven-iron shot to within a foot for another birdie. At No. 6 he hit another seven-iron, this one to within three feet. Another birdie.

At the eighth, Burns hit his worst drive of the day and was bunkered in two. After a 10-minute debate with officials about whether he could rake the trap (he could not), he blasted out and made bogey. But he got that back at No. 9 when he hit a five-iron shot a foot from the cup.

He three-putted 13 for a bogey but hit a fabulous nine-iron flyer 175 yards out of the rough at 14, setting up his longest birdie putt of the day, eight feet. From there he parred in, making an eight-footer at 17 to avoid another three-putt bogey.

So, George Burns, how does it feel to lead the U.S. Open?

"I don't know what to think," he said. "I've never done well here so I don't know what to expect tomorrow.I just hope I can go out there and capture the feeling I've had the last two days. I'm not sure I will because my confidence blows hot and cold. All I can do is try to play steady."

Steady is generally Graham's watchword. He got his birdies early today, four in the first 10 holes. At that point, with Burns teeing off late, Graham led the tournament, with his close friend Nicklaus right behind.

When Graham bogeyed 17, Nicklaus led until his disaster at 16.

The saddest stories today were Arnold Palmer, who quietly shot 78 for a 155, and Lee Trevino, a winner here at Merion in 1971, who had 76 for 148, missing the cut by one shot.