Lee Trevino played a near-flawless, if unexciting, round of 67 today to take the halfway lead in the 109th British Open golf championship at the Muirfield links.

Trevino, the first-round coleader with Tom Watson, has a two-day total of 135, seven strokes under par, and a three-shot lead over Watson, Jerry Pate and 23-year-old Britisher Ken Brown.

There was further thunder over this seaside course 20 miles from Edinburgh, but it was not accompanied by the lightning and rain that plagued the opening round Thursday. Instead, it was the roars of appreciative Scotsmen who scampered by the thousands to get a view of their favorite visitor, Jack Nicklaus. The three-time winner of the event, golf's oldest national championship, rewarded the cheers with an exciting 67, despite a finishing bogey, to get back in the running after an opening 73.

Trevino saved par with a sand shot to within four feet on the treacherous first hole and chipped within a foot to save his 4 on the second hole. After that, he hit all the fairways and greens in regulation. He made birdie on the fourth hole with a 20-foot putt after firing a seven-iron shot at the target 181 yards distant.

He made a 2 1/2-foot putt on the 495-yard ninth following two shots with the driver and a third with a wedge; a 12-footer on the 475-yard 10th hole after a four-iron second shot, and a tap-in on the 542-yard 17th hole after his five-iron chip from just off the green nearly holed out for an eagle.

"Seven more under could win," Trevino quipped. "I'm utilizing all the golf clubs . . . playing the punch shots. I haven't hit a ball yet in the tall rough. I'm keeping the ball out of trouble off the tee."

It was Trevino's accuracy that made his round a bit boring. But the other contenders over this 6,926-yard course sitting on the edge of the Firth of Forth kept the crowd of 29,673 alert.

Pate, playing smoothly following Trevino's example, hitting every fairway after a miss on No. 1, made a magnificent eagle-3 on the 17th to mount his charge. His three-wood second shot came to rest only 10 feet from the hole and he made the putt. A missed six-foot birdie try on 18 gave him 67 for the round.

Brown, who has only one victory to his credit on the European tour, the 1978 Carroll's Irish Open, had a 68 today. It was fashioned on five birdies, two bogeys and two long, par-saving putts.

Watson was even more in the chase until a bunkered second shot on 17 led to a 6, a two-shot swing with Trevino on that par-5 hole. He finished with a 70.

And there were five tremendous roars -- one for each birdie -- and 18 waves of applause -- one for each approach of a green -- for Nicklaus. And one mightly moan as the fair-haired U.S. Open champion bunkered his second shot on the final hole, giving him his only bogey of the day.

Along with Nicklaus at 140 are defending champion Severiano Ballesteros, who posted a 68; Gil Morgan, who shot a 70; Jack Newton, fighting the pain of an inflamed right elbow and totaling 71; scrambling Ben Crenshaw, 70, and big Andy Bean, with a 69.

An added fillip to the day's low-scoring barrage was a course-record 64 by Argentinian Horacio Carbonetti, who got to even par for the tournament after a first-day 78.

The nine-hole record of 30 was tied by Denis Watson of South Africa, whose back-nine tally helped him to a 67 and a cut-making 147. Arnold Palmer was one of those failing to advance to the third round (low 80 and ties) after a 74 today put him at 150.

Trevino, as usual, had a ready explanation for the fine golf he has fashioned this week. Thursday, he said, he went without breakfast because, "A hungry dog hunts best." Today, he decided to eat before his early morning round because, "If you have a full stomach, butterflies have no room to fly.

"I'm not what you would call a three-meal man. I like to drink beer," he added.

Trevino is in an enviable position. His punch-and-run game is suited to this course, well-bunkered to the sides of the greens, but with fairly wide openings in front.And, if the weather should turn nasty again, he also should be able, at least better than most, to cut his shots through the wind.

Watson knows this. "He'll be a hard man to catch on this golf course," Watson said.

If Watson had played the par-5s as he expected to today, he would have an easier job with the catching. Watson overshot the green at the 558-yard fifth hole with a sand-wedge third shot, landing in a back bunker and taking three to get down.

After going five under par with a 20-foot birdie on the par-3 16th, he drove into the right rough on the 542-yard 17th. He "hit a two-iron off the toe into a cross bunker on the right." As many of the players found when their balls were snatched by the fairway traps, Watson could only blast out into the fairway. He hit to 15 feet, but missed for the 6.

"That's just like throwing away three or maybe four shots," he said of his misplays on the potential birdie holes.

Watson says he still is waiting for the wind to blow hard, about the only bad thing, weatherwise, that has yet to happen to this golf course. "When the wind blows, the scores will go up," he predicted. "Especially if the wind comes from the East."

Nicklaus, who played well enough Thursday but could not conquer the slow greens, had little trouble with his putting today. He might have been among those tied for second at 138 had it not been for a miscalculation on 17 and bad luck on 18.

"I felt that coming up on 17 I had to finish 4-4 to get in good position," he said, having gone four under for the day through nine holes, thanks to steady play and fine putting. And a great nine-iron shot out of the deep rough on the 12th hole had set up a 20-foot downhill birdie, his fifth.

Then, he "forgot one of those 153 bunkers, or whatever it is." Nicklaus planned to play the left side of the fairway on 17, knowing that if he drifted a little he could clear the prominent bunker on that side. "I felt like downwind the safety on the hole was to the left if you carried the bunker," he explained. "I forgot the little one behind it. I just wanted the opportunity for eagle."

Instead, what he got was a ball so deep in a bunker that he needed a sand wedge to get it back to the fairway. Even then, he missed a long birdie putt by only a few inches.

On 18, Nicklaus hit a perfect drive and what he thought was a golden four-iron shot to the green of the 447-yard hole. The ball hit about 10 feet left of the pin, kicked straight left and landed in a footprint in a deep bunker. He nearly hit the pin with his blast out, but missed the 10-foot putt.

The only unhappy golfer among the major contenders was Ballesteros, who "felt like a cat" clawing around the course. He said he thought the course would suit him if he were playing well, but "I don't expect too much the way I have been playing."

Even a 68 over one of the great courses in the world can't satisfy some fellows.