Passengers already has refastened their seat belts Tuesday morning for the final approach into Akron/Canton Airport.Pro golfer Lee Elder, a chain smoker, extinguished his cigarette in preparation for landing, but he was still somewhere around 30,000 feet. He has been on a high since winning the $300,000 Westchester Classic five weeks ago.

That was the 44-year-old Washington's secong PGA Tour victory of a year that germinated late and was painfully slow blossoming.

The Westchester triumph, worth $60,000, came only six weeks after Elder had beaten Lee Trevino on the eight hole on an agonizing, not-so-sudden death playoff to win the Greater Milwaukee Open, earning him $30,000 and the third tour victory of his career. It had taken Elders nine years, from 1968 through 1976, to bag the first two.

Two wins in a year automatically qualified Elder for next summer's British Open and his first appearance in the professionally elite, $300,000 World Series of Golf, which begins today at the picturesque Firestone County Club here.

British Open champ jack Nicklaus, tour money-winning and stroke-average leader Tom Watson, and defending champ Lanny Wadkins head a 26-man field that includes the current top 15 U.S. tour money winners, leaders of the European, Far East and Australia Orders of Merit, and the British and U.S. Amateur champions.

Looking back over a career characterized by perseverance and bedrock optimism, Elder considered his milestones - finishing among the top 60 money winners his rookie year on the tour, being the only American black in the first multiracial South African PGA Championship in 1971, winning his first PGA Tour event at Pensacola in 1974, breaking the color line at the Masters in 1975, cracking the $100,000 a-year barrier in 1976 - and decided that his 1978 season has been the most satisfying, the fruition of lifetime's hard work.

This year is the highest point, I'll be well over $150,000. I won two tournaments, and I'm on my way to the World Series of Golf," he said at his flight from Washington, via Pittsburg, taxied to the gate. He was itching to get out on Firestone's immaculately-groomed 7.130 yards where idyllic conditions awaited his final two days of practice for his first tournament since Westchester.

In his last six tournaments, starting at Milwaukee the week of July 2 Elder has finished in sixth place on better four times and earned $116,430.

That Elder should produce the best golf of his career at 44 is all the more astonishing because he had struggled for months going into Milwaukee.

Instead of leaving right after Christmas for the start of the tour - jogging, practicing and exercising himself into shape in California as he usually does - he took his wife on a long-promised vacation. They sunned in the Bahamas, shopped and saw the sights in Paris.

"These are things I wanted to do and I couldn't think of any better time," says Elder. But the late start hurt his golf. "By the time I played a few tournaments and got bck in shape, it was time to leave the West Coast and go South, and I've never played well on the Bermuda grass there."

In his first 18 tournaments of 1978, Elder was among the top 15 scorers only once - a tie for fifth at Greensboro, N.C. He had earned only $29,918. He stroke average was 72.31, compared to 71.57 six tournaments later. Some people whispered that he was washed up. He was frustrated and worried.

"I felt at that time I'd be lucky to make the top 60 money winners and keep my exempt status," Elder admits now. "I felt if I couldn't play better, I'd probably be a 'rabbit' (one of the tour's harried Monday morning qualifying hopefuls) next year.

"That's what's so significant about what has happened since. I know a lot of people doubted I could have a year like this. I had doubts myself.

Elder's fortunes improved after major adjustments in his stance suggested by Trevino on the eve of the Milwaukee tournament, and a late putting lesson from Dave Stockto urged by Elder's wife and business manager - the former Rose Harper ofWashington, herself an accomplished golfer.

The all-important session with Trevino came the evening before the first round, in which they were scheduled to play together.

"Lee's a good friend, and when I saw him I said, 'Aw, man, I'm having so many problems,'" Elder recalls. "He said 'Let's go over to the range and see what's the matter.' I hit a couple of balls and he said, 'I can see your problem right now.'

"Basically I was standing too blocked to my intended target. My left shoulder was pointing right on the line I wanted to go, rather than open to my intended line. I had to come over the top and pull the ball back on my target, so I was hooking.

"Lee saw that I couldn't get my hands by my body freely, opened my stance, had me drop my left foot back, and said, 'Now go ahead and swing.'

"It was like night and day. After just eight or 10 balls I knew this was the right thing. My balance was better. I thought it would take some time to get comfortable and hit good shots under pressure, but right away my game picked up and kept improving."

Elder shot 69-70-70-69 at Milwaukee, but lost a two-stroke lead on the last three holes of regulation play before finally shaking Trevino in the second longest sudden death overtime in tour history.

"When I made a mistake and bogeyed 16, Trevino said to me, 'Okay, Pro, let's tighten it up.' He seemed to be still pulling for me. That woke me up," remembers Elder, who considers Trevino the most unselfish and helpful of tour rivals.

"When I won, we embraced. He said, 'I'm so happy for you. I'm the happiest man in the world. It's just like me winning.'"

A 60-foot wedge shot from the left rough - "the greatest shot of my career" - set up a 1 1/2-foot putt for a birdie on the final hole at Westchester, giving Elder a 10-under-par four-round total of 274 and one-stroke victory over Mark Hayes.

"That had to be the greatest thrill, the highlight of the year for me, because I beat such a great field," Elder says. "Every top player on the U.S. tour except Trevino and Gary Player was at Westchester."

Among the rewards that followed were lucrative new deals to do commercials and personal appearances for Michelob beer, Gulf Oil and Oldsmobile cars. Several existing endorsement contracts for golf wear and equipment were increased.

Meanwhile, Elder decided to take another vacation - "I told Rose that when I reached $100,000, we'd go on a trip someplace" - but changed plans when his eight-year effort to assume the concession contract for Washington's Langston Golf Course was finally rewarded.

Elder knows that the most appropriate lasting tribute to his accomplishments would be a rejuvenation of the long-neglected 18 holes at 26th Street and Benning Road NE near RFK Stadium, where he and so many other black golfers developed their games. By the end of the year, he will have invested $100,000 toward refurbishing the course, which will serve as the future home of his annual summer clinics for Washington youth.

Elder had planned to play one tournament between Westchester and the World Series, but the death of his godfather interceded.

Two weeks ago he hosted the annual Lee Elder Pro-Am at Williamsburg, Va., to raise funds for his national scholarship fund, and he didn't want to go all the way to Napa, Calif., to play last week because he has a stenous schedule coming up. He leaves Monday for the Pacific Masters in Tokyo, then the Colgate Match Play in Britain, and will fly back the evening of Oct. 15 in order to make a speech for the Urban League of Richmond the next day.

Elder loves Firestone, where he last played in 1975. "I like the texture of the greens and the fact they have very little hidden roll and trickery," he said yesterday.

"My game is a lot better suited for this course now becuase I'm cutting the ball, moving it from left to right, instead of drawing it. This is a course for left-to-right strikers of the ball. And I'm driving the ball a lot further than I was as a rookie."

It was here that, in the American Golf Classic of 1968, he lost a dramatic, nationally televised playoff to Jack Nicklaus on the fifth hole of sudden death.

A 34-year-old tour rookie with 10 years experience as a pro hustling and playing black tournaments (he won 21 of 23 at one stage), Elder had finished in the money in his first nine events - something no PGA Tour newcomer achieved before or since. Now he was on the threshold of his first tour victory, but Nicklaus sank tough putts of 30 and 25 feet to keep pace after Elder twice had apparently seized victory.

Finally Nicklaus, who made a last impression on Elder as "the toughest competitor, head-to-head, I've ever met in life," won with a birdie, Elder sliding a 30-footer to match him just past the lip of the 17th cup.

Elder remembers graphically every stroke and nuance of that playoff, and discussed it in such detail that, to him, "it seems like yesterday." He recalls feeling "like a man kicked in the shins."

People who saw it on TV constantly remind him of it, but Elder is convinced that, in the long run, it is best he lost and didn't record his first tour victory for five years.

"I was new to the tour, my wife wasn't my manager yet, and I think success so early would have spoiled both of us. It would have seemed too easy. I might have gotten cocky, not worked hard to develope consistency. I wasn't ready and if I had qualified for the Masters, I might not have had the goaI and drive I did later," he says.

Instead of cockiness, Elder cultivated respect, dogged determination, uncommon patience and decency - qualities that should be revealed in his life story, entitled, "Only the Ball Was White," published by Random House next Spring.

ELder, who has been working on his biography for three years, finds it significant and heartening that he is no longer systematically referred to as "the first black to . . ."

"I'm the first black to play in the World Series, but no one is dwelling on that. Instead it's the first time that Lee Elder, the golfer, is here and has a shot at the largest prize in golf," he said yesterday.

If he were to win, his victory would be cited as a great personal and professional landmark, not a racial or social breakthrough.

"And," noted Elder, "even though this year already has given us the last chapter we needed, my winning the World Series would be a great way to end the book." CAPTION: Picture, Lee Elder lines up $60,000 birdie putt on 72nd hole at Westchester Classic, AP