Hale Irwin marched toward the green of the 523-yard 13th hole where his ball lay just inches from the cup, awaiting his tap-in for an eagle.

"What did you hit, Hale? Whatcha nail it with?" pleaded a dozen voices in the huge U.S. Open gallery at Inverness.

Glancing sideways mischievously, Irwin punched his fist at the crowd, then flashed two fingers and a grin.

What he meant was "two-iron." What it looked and felt like was "victory."

Irwin, the expressionless master of the long irons who plays best on the meanest courses, scorched the Inverness monster for a four-under-part 67 today to take a three-shot lead after three rounds of this 79th Open.

The only man within five shots of Irwin at 209 was his long-time friend and rival, Tom Weiskopf, 212. The veteran master golfers played eye to eye, Irwin in the pairing behind Weiskopf. Both fired 67s - the best rounds of the week.

That classic pairing - the stolid, imperturbable Irwin with the serviceable swing and the fierce scrambler's will power against the emotional tinderbox Weiskopf with his textbook swing - may well dominant Sunday's proceedings.

Nevertheless former Open champ Jerry Pate and Tom Purtzer stand poised at one-over-par 214, while Lee Elder and Larry Nelson are just a stroke further back.

The unquestionable highlight to today's Irwin versus Weiskopf duel, and perhaps the crescendo of this Open, came at the par-5 13th where Weiskopf made his boldest bid - a 10-foot eagle putt. Irwin upstaged him seconds later with a "gimme" eagle to match.

"I was watching Tom all day," admitted Irwin, who was savvy enough to anticipate that the two second-round leaders, Purtzer and Nelson, would fade - as they did with a 75 and 76, respectively.

"I'd been making birdies all day," said Irwin, who had six in addition to his eagle - two of them coming from off the putting surface. "But Tom kept matching me."

When Weiskopf trickled his eagle putt into the cup, the Open had taken on a clear definition. Irwin stood at three-under par, Weiskopf had jumjed to one-under and no one else on the leader board was in red figures. The big guns had moved into to position and firing had commenced.

Irwin stood in the center of the sloping, sidehill fairway more than 300 yards from the tee. He took eight paces in from the sprinkler head that was 216 yards from the front of the green. "It's 226 yards to the pin," he muttered.

Deliberately, firmly, as he strikes all his shots, Irwin nailed the long iron - always the hallmark of his game. "Oh, yes," a pretty good shot," he said slyly afterward. "Near about as good as I can hit it."

The crowd gave an ovation worthy of a spotlight moment in Open history as the ball stopped - dead on line - just a few turns short of a double ea-

"That was the high point of the day, no doubt," said Irwin, who also chipped in from the fringe at the par-3 third, and putted in from the frog hair at the par-3 12th.

"Tom was making his presence felt. When you put that eagle in right on top of him, you're saying, 'You may have gained on a lot of people, but you haven't gained on me.'

"I had gone birdie-birdie-eagle. I literally floated, or more like flew, to the next tee. I was so anxious to keep that momentum going. And then . . . we waited."

A delay to allow the crowd to cross the fairway broke Irwin's concentration, otherwise much of the drama might already have gone out of this tournament.

"You're unaccustomed to huge volumes of crossing traffic," said Irwin. "I broke my mood and it annoyed me. It was my fault. I didn't handle it well."

Irwin, who had made back-to-back bogeys at the sixth and seventh when he missed the greens, did the same at the 14th and 15th.

"I had to get it back," said Irwin. And he did, rolling in a 25-foot birdie putt at the 432-yard 17th to push his lead which had dropped from four to two, back to three.

"Yes, I'm definitely ready to win again," said Irwin, who, despite more than $1.5 million in career prize money and six straight finishes in the top seven in winnings, has not captured a tournament since October 1977.

"I can taste the blood, if that's what you want to call it," said the former defensive football halfback at Colorado, who won the 1974 Open at the over-par massacre of Winged Foot.

"But," said the wry Irwin, running his tongue over his teeth, "the thing I can really taste is these new braces."

Rarely have two men wanted a major title as much as Irwin and Weiskopf. Both have endured much criticism.

Irvin always is cited first ast that bane of the PGA - the check-casher who makes a fortune but lacks the flair to win. Weiskopf is exhibit No. 1 of a tremendous natural talent who constantly thwarts himself with a foul temper. Despite their status as golf millionaires, each has won only one major title in a total of 28 seasons between them.

Weiskopf, currently 96th on the money list, is particularly desparate to rehabilitate his reputation. He to rehabilitate his reputation. He worried himself into an ulcer that took him off the tour earlier this spring. He has been strong enough to hit practice balls for only a month.

"The first tournament I ever saw was here at Inverness - the '57 Open when I was 14," said Weiskopf, a Buckeye. "My dad brought me and I thought those guys were gods. Sam Snead with that majestic swing and Cary Middlecoff meticulously grinding his way to a playoff tie.

"I watched the frustration of the players and their joy. It created the desire in me to become a golfer," said Weiskopf. "Every putt that broke two feet that summer, I'd pretend I was Middlecoff."

Perhaps those reveries had Weiskopf in one of his rare blissful days when he was not throwing club or arguing with spectators or photographers - as he was in a blue-funk back-nine 40 in the second round. Or perhaps the presence of only one bogey on his car helped.

"I don't know why I was in such a fine golfing mood," said Weiskopf, who often seems too thoughtful and sensitive for his own golfing good. "I guess I just made up my mind that I was capable of doing anything I wanted to do."