Stan Smith was in street clothes, on his way to the dressing room to change into tennis gear for his first-round match in the $125,000 Volvo Classic, a match he was destined to lose ingloriously to Brian Teacher, A man stopped him in the corridor of Smith Center. "Excuse me," the man said "but could I have your autograph for my wife?"

"Sure, Smith said. He waited patiently as the man fumbled in the breast pocket of his corduroy blazer before producing paper and a pen.

"What's you wife's name?" Smith asked.

"Patty," the man replied.

Smith started to write, then hesitated "Patty with a y, or an i?" he asked. Informed that it was with a y, he proceeded, personalizing the autograph with a little note.

Cynics might say that Stan Smith can linger over autographs now because he isn't asked for nearly as many as he was in early 1973, when he was the reigning Wimbledon champion and, at least briefly, the best tennis player in the world.

The fact of the matter, however, is that Smith's courtesy -- refreshing in an age when so many pampered tennis stars are brusque and selfish and consider it an imposition to be asked to scribble their names -- is not a trait acquired lately. He was always like that.

When he was leaving the court -- dejected at having double-faulted away three games in a 7-5, 6-2 loss to Teacher, his second first-round defeat in as many weeks -- a boy stopped and asked for his autograph. Again, there was an awkward moment of delay while a pen was found. Smith waited. He signed.

Few professional athletes have ever dropped from the pinnacle of their sport back into the rank-and-file more puzzlingly than Stan Smith.And few have accepted the disappointment with greater strength of character, more grace and less self-pity.

"Stan is unbelievable," says Margie Gengler Smith, his wife of six years, an intelligent and sensitive woman who captained the women's varsity at Princeton and played briefly on the women's pro circuit. "I know that after he loses he doesn't feel like being nice, but he's patient with everybody. He signs autographs, talks to people, lives up to his commitments. He doesn't mope. He doesn't take his frustration out on anybody.

"It's easy to look up to somebody like Stan when he's winning and say, 'Isn't he a wonderul person.'

But people also can really admire the way he is when he loses, and that's really a great test of his faith."

Faith has always been important to Stanley Roger Smith. A member of the Fellowship of Christian Athletes in his college days at the University of Southern California, he believes -- and has said many times -- that his responsiblity on earth is to get the most that he can out of his God-given talent.

The long and curious slump that has dropped him from No. 1 in the world to just another player on the tour -- ranked No. 22 at the moment -- has shaken his confidence in his tennis ability, but never his faith.

"I feel I'm kind of being put through a test in a way," he said a few years ago. "You learn lessons when you lose that you might not learn when you win. It's another experience. It's not much fun, but I think you learn the facts of life, and it's a useful experience in the long run."

The ordeal of losing -- of falling short of the Wimbledon and U.S. Open titles that he long thought, earnestly thought, he could win again -- has lasted longer than he ever imagined. He is not sure now of his true potential. "I've got mixed emotions about it," he said yesterday. "Sometimes I think still can, and other times I don't think I can at all."

The only thing he truly wants is to know is that he has done the best he can. He says that if he can look at himself in the mirror and say honestly, "I worked hard, I gave my full effort, I didn't give up, and I remained true to my ideaals," he will be satisfied, win or lose.

"Obviously the story would be wonderful if I won Wimbledon this year and then retired," he said. "That's kind of the way people think of things: you play, you make your name, and you quit at the top. But life isn't quite like that. It's a little bit unrealistic.

"In a way, it's more of a challenge now than it ever was before . . . . To be able to keep up the same outlook on life, the same attitude, when you're struggling that you had when you were winning easily, that is a real test of character.

"The prayers that I have now are not necessarily to win every match, but to have the right attitude on the court. The worst thing would be just to go through the motions. Whether I win or not, I want to know that I fought the good fight. If I know that, I won't get discouraged if I don't win tennis matches."

Smith is not a bad player now. No one his age (33) or older is ranked higher. He won $158,431 in prize money last year -- a good chunk of it in doubles, since he and Bob Lutz remain one of the world's premier teams -- and earned perhaps twice that amount in endorsements and investments.

His wife and 18-month-old son, Ramsey, travel with him on the tour. Smith is well enough off financially that he can afford to bring a full-time babysitter along, an Englishwoman named Mandy Ripley who celebrated her 24th birthday yesterday. All the Smiths adore her.

Most players would consider this life heavenly, but to appreciate Smith's attitude fully, one must realize how good he was.

This Smith, a mighty man was he -- U.S. Open champion in 1971, Wimbledon champ in 1972, WCT champ in 1973 (when he beat his leading rivals, Arthur Ashe and Rod Laver, for the honor), the top-ranked player in the United States four times.

The disconcerting thing was that Smith did not go downhill gradually. That would have been understandable.Instead he plummeted just when he seemed to be at his peak, for no apparent reason. Later his attempts to regain his world-beating form were retarded by a presistent tennis elbow and other injuries that forced him into bad habits on his strokes. But initially, there was no explanation for his fall. He just stopped winning.

Suddenly, inexplicably, he started losing close matches. He had a match point against Jan Kodes in the semifinals of the U.S. Open in 1973, and lost. He led Ken Rosewall by two sets to love, 5-2 in the third and had two match points in the semifinals of Wimbledon in 1974. Again he lost. A pattern was established. Instead of playing to win, aggressively, he tried not to lose and played tentatively cautiously. It wasn't his style.

No one has ever explained satisfactorily what precipitated the fall. There are explanationa galore for why it continued -- the painful elbow, eroded confidence that made him play even more defensively when he should have attacked, the trend to slow courts which did not suit his serve-and-volley style, the influx of richly talented new champions such as Jimmy Connors and Bjorn Borg But no one has ever figured out why Stan smith's slump began in the first place and that is what haunts him, because he is not sure deep in his heart that he cannot win the major titles again.

"I just don't know. It's such a thin line between winning and losing. Sometimes I feel I'm right on the verge, and other times I feel a million miles away," he said yesterday.

"I started out this year really eager. I'm thankful that my arm is all right. I don't have any injuries or any excuses. Basically, I'm moving well and hitting the ball solidly. Two weeks ago at Denver. I almost broke through. Then the last weeks, I haven't played well at all. My serve has let me down, and I don't understand why. I don't know what I'm doing wrong; that's the unsettling part.

"At times during the last year or so, I've really felt that I was playing well enough to win any tournament even to win Wimbledon or the U.S. Open again. When I won the Grand Prix tournament in Vienna last fall, I played extremely well in the final (against Wojtek Fibak). I won 15 games in a row and kind of got into a zone where I wasn't thinking about how I was hitting the ball or a lot of other things.

"I was just playing, and it was instinctive. That's when I have always played my best tennis. There have been about a dozen occasions in my life when I've played like that -- moving so well and hitting the ball so sweetly that you're not worried or concerned about anything. It's a great feeling.

"I think if I served really well and got into a streak of returning serve well, maybe I could win one of the big tournaments again. But other times I feel like I'm just spinning my wheels and getting nowhere.

"I don't want to waste my time. That would be the worst thing. If I hang in there, and work hard and prepare for every match, then I'm not wasting my time, whether I win or lose. But if I start going out there and just trying to get by, if I get discouraged and don't hang in there, that's when I'm wasting my ability, and ought to do something else with my life."

Smith sat down at the beginning of this year and set goals for himself in several areas of his life. His tennis goal is to finish among the top eight players in the Volvo Grand Prix standings for the year.

"But whether I make that or not, I want to be able to look back at the end of the year and say I did everyting Could -- I practiced hard, I picked out the parts of my game that needed work and worked on them I planned my schedule carefully and stuck to it, and I hung in there every match and did the very best I could," he said."If I can do that, then I won't have any regrets, whether I accomplish the goal or not. If, I can't say that, then I'll be kind of discouraged.

"I don't want to waste any years of my life, but I don't think I will be as long as I do everything to get the most out of my potential, whatever that may be. I wonder sometimes. But I thing I'm certainly a better person because of what I've gone through the past five years than I would have been if I had quit in 1973, or not gone through injuries and losing. Maybe this experience has punched a hole in my pride that needed to be punched. Maybe my pride was too strong."

If his ordeal has been a test of character, he has passed splendidly. This Smith, a mighty man is he still.