Sampras understands all this; he is a person comfortable in his own skin. He does say, ““There is no high like waking up knowing you’ve won another major - nothing like it.’’ But he also knows that it is almost incidental how many more Wimbledons he wins, or how many more Australian or U.S. Opens . . . if he doesn’t just once win at Roland Garros, there in the Bois de Boulogne, on the red clay. If Pete Sampras doesn’t win one French Open.

But should he win one? Win one French and, very likely, he will walk off into history acclaimed the greatest tennis player ever to stride a court.

In Monte Carlo a couple of weeks ago, where Sampras had gone to prep for the French in a clay tournament, he lost in the first round to a clay-court Swede you’ve never heard of. Afterward, he went out to dinner with Bjorn Borg, the old champion, who is the only player in the post-1967 Open era with more Grand Slam event titles than the nine Sampras has. And there, it occurred to Sampras that although he is still only 25, he is already older than Borg was when he retired. The year Borg quit, 1981, he was still superb - even winning his fourth French Open. But he lost the U.S. Open finals for the third time. Just as Sampras can’t win the French on clay, Borg couldn’t win the American on hard court. And that one searing frustration drove him from the sport. ““It killed Bjorn,’’ Sampras says. ““He told me that.''

Usually, in fact, one of the four disparate majors defies even the very best players. Only four men - Fred Perry, Don Budge, Rod Laver and Roy Emerson - have ever managed to win all four in their whole careers. No one has won all four since Laver swept the Grand Slam in 1969. Fred Stolle, himself a French and U.S. champion, who saw Laver perform that feat, says flat out: ““It’s all but impossible that anybody can ever do it again.’’ There is a greater variety of surface now, much more competition. ““Laver told me he only had four or five good clay-courters to worry about,’’ Sampras says. ““I got 50.''

His quest for Paris, which begins in two weeks, is so historically substantial that Nike - that official certifier of significant things athletic - has already made a commercial hyping the challenge. But Sampras himself is a man of little conceit, who stares at his strings even as the crowds cheer him. He talks of Ivan Lendl, who could win every major but Wimbledon; who, haunted by that failure, built his own grass court and gave up all for that lost crusade. And Sampras chuckles. ““Look, I’ve pretty much done everything I can, except win the French, but I’ll never be obsessive about it - like Bjorn with the Open, like Lendl with Wimbledon. How can I?’’ He shrugged. ““I’m not obsessive.''

He was sitting in the shade at Saddlebrook, the resort near his Tampa, Fla., home where he practices. He was resting now between two grueling clay-court sessions. Sampras had recently learned, to his dismay, that Michael Stich, the ‘91 Wimbledon champion, had announced his retirement, still only 28. The young drop like flies in tennis, burned out from a globe-girdling, year-round life that starts too early, wears too thin. ““Tennis is unique,’’ Sampras says. ““You’re completely alone. I saw where even Mike Tyson compared it to boxing. But in tennis, there’s nobody to go back to the corner to every couple minutes. No caddies. Nobody. Just you . . . and the other guy across the net.’'

Yet, even though Sampras started touring before he finished high school, he was never the fragile man-child. For that matter, there has always been an almost eerie disjunction of age with Sampras. As a skinny little kid, he agreed, on sheer faith, to be transformed from a safe defensive baseliner into a classic risky serve-and-volley model - yet who could imagine that the child of parents 5 feet 10 and 5 feet 4 would grow to a hunkish 6 feet 1? Then, at the age of 19, altogether innocent of the other sex, Sampras abruptly took up with a woman named Delaina Mulcahy, seven years his senior. His important male relationships have invariably been with older men - and two of his dearest friends, his coach, Tim Gullickson, and the ex-player Vitas Gerulaitis, have died in the past few years. ““I never have any close friends my own age,’’ Sampras says. And then, without any self-consciousness: ““I know that’s not normal, but it’s just the way I am.''

Probably, this sort of laissez-faire attitude enhances his chances to overcome his obstacles of style and, at last, to win the French. But the problems are manifold. It is not just that clay plays so much slower - a virtual ““mud,’’ Sampras says, on those cool, damp days so common to Paris in the springtime. ““It’s the slipping and sliding,’’ he says. ““Balance.''

After all, red clay is really only dirt in makeup. Harry Hopman, the Australian martinet, would even make his players shower with their clothes on to rid themselves of the ugly alien substance. But for Europeans raised on the grubby clay courts, it is mother’s breast, and so, at Saddlebrook, Sampras spends hours rallying interminably in the Continental fashion. Thomp, thomp, thomp - long point after longer point, in the parched sunlight, gulps of Gatorade, gasps for breath. Last year, playing a tough draw in an uncommonly warm Paris spring that turned the mud into some sort of sandy tile, Sampras went down in the semis, ““out of gas.''

Yet, really, it is the mental adjustment that is most difficult for hard-courters, underscored by the fact that the clay-courters know - and they know Sampras knows, too - that he is not invincible in their brier patch. Of the last 12 Grand Slams other than the French, Sampras has won eight - a run not even Borg matched at his height. But put Sampras in Paris and he is a roman a clef for all those Americans who have come a cropper there through the years. ““I just never thought I could do well on clay,’’ he says with a sigh. ““It’s not realistic. So much of it is what you grow up on. It’s not just a different surface. It’s a whole different attitude.''

A serve-volleyer like Sampras instinctively looks to move forward; a clay-courter moves laterally. A player like Sampras is impatient and aggressive; a clay-courter is trained to be patient and defensive (at his worst, he plays not to lose). And while Sampras is a calculated strategist, hardly a devil-may-care rake on the court, the game he is passionate for is the tennis of fire and dash. When he closed out a point in practice the other day with a winner on the clay, he screamed: ““I need to play again! I feel it in my blood!’’ On to Europe.

Indeed, unlike so many tennis players who flame out by Sampras’s age, he seems poised to fire the second-stage rocket. ““My God,’’ he called to Borg at their dinner, ““what would I do with my life if I quit now, like you did at my age?’’ Even - perversely, it seems - his body is catching up with his mind; he is actually getting in sync with his age. Sampras broke up with Mul- cahy last fall (she is currently offering the wisdom of her advanced years to a 23-year-old on the Houston Rockets), and now, in 1997, he has worked himself into his best shape ever, has won the Australian in wilting 120-degree heat and is dating a gorgeous new woman.

Never mind her name, Pete (we have to leave something for the London tabloids to work on at Wimbledon), but what’s her age? ““Hey, she’s 25.''

So, finally, you’re normal; at last, you’re actually playing with somebody your own age.

““I like that, I like that,’’ he hoots. And then, more seriously: ““You know, I’m fine. I know what I want, and I’ve never been happier in all my life.''

And so, then, do you, Pete Sampras, think you can win the French?

““Yes, I do. I do believe now that I can win the French Open.’’ So has confidence cracked open the last door to immortality.