On a bitterly cold, wildly windy day that made the seaside Royal Lytham St. Annes course a nightmare for almost everyone else, the proverbial unknown British golfer, Bill Longmuir, shot a scrambling six-under-par 65 to take a three-shot first-round lead in the British Open today.

Making up for wind-blown wood and iron shots with uncanny putting, Longmuir carded six birdies, five in a row, in the first nine holes for a 29 that tied the British Open record. Then, in his words, "I just hung on grimly" over the more treacherous back nine for the 65 that equaled the best round shot in six previous British Opens played here.

Longmuir, a rakishly handsome, compactly powerful 26-year-old, is the ideal sentimental local favorite for the Open championship. A native of the area east of London who considers himself a Scot, like his professional soccer player father, he has won as many discotheque personality contests as he has gold tournaments - two.

"I putted fantastically today," Longmuir said after holing a number of 10-, 20- and even 30-footers and never three-putting on the bumpy, unpredictable greens.

"It's a tough course and I thought I'd have to shoot very well just to make par."

His closest pursuer was U.S. Open $&(WORD ILLEGIBLE champion Hale Irwin, who shot what he called "a well-managed" 68. With three birdies and no bogeys on the final nine holes, Irwin was one of the few golfers to gain ground playing into the teeth of the blustery wind on the way back to the red brick clubhouse.

"On a day like this, fighting against the wind all the time on the back nine, you have to go out and manage the best you can," Irwin said. "I like my position. I feel better than after the first round in Toledo," where he shot a 74 on his way to winning the U.S. Open last month.

Just behind Irwin were Jerry Ate, the U S. Open winner in 1976, who shot 31, 38 for 1 69, and Japan's Isao Aoki at 70. Pate, who collected an eagle, five birdies and five bogeys, compalined that the wind hampered his usually accurate driving by disrupting his relatively slow swing.

"British players learn to play a quicker swing in the wind," he said. "If I get wind here, I have a heck of a time. I can even hear my club going back in the wind."

At par 71 were Lee Trevino, former U.S. Open champion Orville Moody, British amateur Peter McEvoy and Australian Terry Gale. Grouped with five others at 72 were the two most recent British champions, Tom Watson (1977 at Turnberry in Scotland) and Jack Nicklaus (last year at St. Andrews in Scotland).

After a hole-in-one with a five-iron on the 212-yard, par-3 fifth hole and finishing the front nine in three-under 32, Nicklaus became one of the many victims of the head winds, cross winds, narrow fairways, high rough and plentiful sand traps of the back nine. He felt he wasted the hole in one, his fourth in a professional tournament and 10th of his career.

"I let a good break and a pretty good round get away," he said, looking weary. "On a day like this, with the wind, you have to make your putts if you want to score."

Despite feeling uncomfortable with an altered putting stance suggested by his son, Jackie, he three-putted two greens and narrowly missed several birdies and pars on makeable putts elsewhere.

"My putts were reasonable," he said, "but they just didn't go in."

There were plenty of other victims of this course a few blocks from the sea in an old beach resort town south of Blackpool on the western coast of Britain.

While most of the front nine is downwind and partially protected by trees and a fence along a commuter railway line bordering the course, the back nine is completely exposed. Today's strong head winds made the six consecutive par-4s at the finish play like 5s, with few able to reach the greens in two shots. Those tough closing holes also are full of twists and turns o greens hidden behind high mounds and sand traps.

Among the victims of the back nine were three men playing in a British Open for the first time: Lee Elder, Masters champion Fuzzy Zoeller and Gary Player's 17-year-old son, Wayne Elder, of Washington, D.C., was one under par on the front nine but lost five strokes on the back for a 75. Zoeller went out in par 35 but blew to a 43 on his way back for a 78.

Wayne Player, who scored well enough in two qualifying rounds earlier this week to make it into the Open, excited the crowd following him and his father in back-to-back threesomes by shooting a 33 on the front. But he couldn't keep the ball on the fairways and greens on the back nine, taking a 42 for a total of 75. However, he stayed ahead of his father, who shot 77.

Longmuir was playing in his second British Open, having gained entrance through qualifying rounds both this year and last after failing three times before. After winning less than $7,000 in tournaments each of the last two years, he was as well known as the two tournaments he had won in 1976 - The Nigerian Open and the Southland Classic in New Zealand.

"I don't believe either the score or the person," Nicklaus said. "I think he's just some fictitious person you put on the top of the scoreboard. Where is he from, anyway?"

He is from Essex, but his father, who played soccer in his native Scotland, has decreed that both he and his son are Scots.

Longmuir started playing tournament golf in 1976 after driving a truck "when I was flat broke."

The nest egg for his first tournament came from an Essex golf club he once was attached to and money he won in male personality contests at discotheques where he spent his free time.

He said friends who ran the discotheques talked him into entering the contests in which he was voted Mr. Talk of the South Club and Mr. Basildon, an Essex town.

"It was all a big laugh," he said, "except for the $600 that came with each title."

Longmuir, who was one of the first players to tee off in a light drizzle early this morning, sprayed his drives and approach shots liberally around the course. But he always seemed to get a good lie in the rough, a lucky bounce onto the fairway or a long putt down when he needed it most. CAPTION: Picture, Bill Longmuir