Andy North sank a 45-foot birdie putt on the 18th hole, minutes after Gary Player had a birdie from seven feet, to protect his lead yesterday in the third round of the 78th U.S. Open golf championship.

North posted a par 71 for a 211 total, two under par. Player, the Masters champion, scored 70-212 to take second place, two strokes ahead of J. C. Snead and Dave Stockton, at 214. Snead had 72, Stockton 70.

Andy Bean (71), Spain's Seve Balesteros (71) and Johnny-Come-Lately Miller are tied for fourth place at 215, Miller registering the best round of the tournament, a 68, after Friday's 69.

Jack Nicklaus went three over for the day to come in at 216. The three-time Open champion was in good position until the 13th hole when he put a wedge shot into the creek guarding the green, then shot over the green into a trap and wound up with a triple-bogey 7. Nicklaus is tied with Billy Kratzert and Tom Kite, five shots behind North.

Mac McLendon and Bruce Lietzke round out the leading contenders, at 217.Hale Irwin, the first-round leader, faded to 218 with a 75 as did Lee Trevino.

The day's pivotal hole was the 11th, a 594-yard par-5 that had held up well under long-range bombardment from the fairway the first two rounds. The last two twosomes stormed through there six under yesterday, however, Nicklaus and Snead bagging eagles while Palyer and North birdied.

Nicklaus and Snead were sadly in need of a reverse twist by then. They had started play at even par, two shots behind North, only to fade slightly at two over and three over respectively, while North and Palyer held steady at one under.

The effect of the 11th on Player, North and Snead was positive, buttressing their confidence at a vital stage of the tournament. But Nicklaus, the favorite, looking for his fourth Open title, could not stand prosperity. Two holes later, at the 13th, generally regarded the easiest par 4 on the tough back nine, Nicklaus took a triple-bogey 7, placing him six shots behind Player and five behind his partner, North.

Johnny Miller bounced into the championship picture early in the day by registering a four-under 68, the best score of the tournament.

Miller had begun his long-awaited comeback Friday, with a 69, but it followed a 78 on Thursday and another excellent effort was required if the 31-year-old player from Napa, Calif., was to threaten the leaders. He delivered, not missing a fairway or a green until the 11th hole.

"It's nice, beginning to feel I control the game instead of it controlling me," the 1973 Open winner (at Oakmont, Pa.) declared. "I've been so far down, the last two years, it's a thrill just to be playing this good, even if I don't win.

"On the 18th for instance, I hit a four-wood into the fairway, then I let everything go with the four-wood again, from 250 yards out, and it was everything I wanted. It was a little like the old days, being able to hit the big shot when I needed it."

The "old days" for the tall, slender blonde weren't really that long ago. The most promising player in the nation in the early '70s, Miller has slumped miserably since the winter of 1976 when he captured the Tucson Open, the Bob Hope Desert Classic and the British Open.

"Byron Nelson has been most helpful in helping me get straightened out," Miller said. "He got me behind the ball a little bit more, and not worrying about everying at once. Before I started with Byron I was pretty pathetic."

Asked about the steady stream of criticism he has suffered recently, Miller replied, "I deserved it. I was playing that bad. But I didn't sit on my rear. I've worked hard to get back."

And now?

"I still don't expect too much, being two over. I don't know if I'm ready to win, yet. But those last six to eight holes are tough. You guys might be surprised what the best score is at the end of the day."

"The course should play a little easier today," Hale Irwin commented shortly before starting out. "It's not as hot, there's not that much wind, and we're all a little more familiar with what's out there.

"But there is one increasing problem," the first-round leader acknowledged. "As we get closer to the finish the collars are going to feel tighter and tighter on everybody."

It didn't take long for Irwin's observation to become apparent.

Old pro Lee Trevino and 18-year-old amateur Bob Clampett both suffered double bogeys on the comparatively easy first hole. Both had started off one-over, only three strokes behind North.

"I don't know what it will be like, playing with one of the great players," Clampett had said. He quickly found out. Trevino hooked his drive, hitting a tree. He got back onto the fairway, was short of the green from the heavy rough, then was short again pitching toward the green. A putt of four feet saved him from an even worse fate.

Clampett, a freshman at Brigham Young University, had plenty of time to observe all this - and wonder if he might not be better off back with the unknown pros he played with the first two rounds. The young man was only a few feet from the green in two, only to take two swipes at the ball and come up with nothing. His third chip attempt from the taller grass was excellent, to within inches of the pin.

As they left the green both players had had the experience of one-putting for a combined total of 12 on the par-4 hole. Both bogeyed No. 2, too, and wound up with 39s, four over, at the turn, posting identical cards.