WHEN THE New York City Ballet returns to the Kennedy Center Opera House Wednesday night to begin a two-week engagement, just about the biggest thing in sight -- both literally and metaphorically -- will be dancer Peter Martins. Given his commanding height, gridiron frame and blond, stern, Nordic good looks, the company's Great Dane has always been physically prepossessing. Over the past decade, as his artistry has matured and his stature has been enhanced by the growing frequency and challenge of his assignments, he has been unofficially acknowledged as the reigning male star -- in a company that purports to shun stardom.

However, Martins is coming up on his 36th birthday, a juncture in a ballet dancer's career when thoughts of professional longevity begin to loom large. Does he ever think about stopping, and could he live without it? "Better," he says unhesitatingly. "Yes, I think about it a lot. I cannot bear to see wonderful dancers pushing themselves beyond their prime. But who are we, who is anyone to say when a great artist should no longer perform? It's certainly true that older, more experienced artists often have things to offer, beyond technique, that virtuosic youngsters can't possibly have acquired yet. And the fact is, most dancers can use the money. I could use the money. And I like being on stage, and maybe I too have something to offer now that I didn't in earlier years.

"But the basic point," he adds quickly, "is where my interests lie. I can't afford to spread myself too thin, and my major interest lies with other dancers -- in teaching, coaching choreographing. At this point in my life I find these things far more stimulating than working with my own body, which I've done for 20 years to the exclusion of almost everything else. I can't really say when I might quit -- a year, two years, six months. I'd rather stop when I'm still decent to look at. In any case, I'm convinced I won't miss the stage."

Martins was reached in New York as he was leaving for Paris with companion NYC Ballet dancer Heather Watts. (The couple danced there as guest artists with the Washington Ballet this past week.)

In recent years, his career has expanded considerably. Not only has he become an avid and prolific choreographer -- we'll see another two ballets of his for the first time in the coming Kennedy Center visit -- but he's also been increasingly active as a performer and organizer in side tours with small groups; a short while ago he was named "artistic advisor" of the Pennsylvania Ballet, when that company hired former NYC Ballet principal Robert Weiss as its new director; at the end of this month, "Far From Denmark," Martins' first venture into autobiography, will be published by Little, Brown; and just a year ago, the NYC Ballet designated him a "ballet master," meaning that henceforth he'd share choreographic and administrative duties with George Balanchine, Jerome Robbins and John Taras, the others who bear that title.

All these developments cumulatively have fueled speculation -- rampant in ballet circles for the past few years -- that when the inevitable day arrives when Balanchine wants to or has to relinquish company leadership, the mantle will fall most naturally and logically upon Martins' broad shoulders. Mind you, there isn't any hard evidence, and certainly no substantiation from within official NYC Ballet ranks, that such a decision has been made or even contemplated. The closest thing to confirmation, perhaps, is the opinion often expressed by the company's co-founder and Balanchine intimate, Lincoln Kirstein, that Martins has all the prerequisites for the job. Still, Balanchine is 78; he is just recovering from a cataract operation and had heart bypass surgery a few years ago. Predictably, the rumors of succession persist. Indeed, one of the only people in New York who doesn't seem convinced that he is the heir apparent is Martins himself.

True to his reserved, almost austere temperament, Martins appears to detest scuttlebutt and "insider" intrigue.

"The only place these things get talked about is in the press. Not in the company itself. As for Mr. Balanchine, he's still recuperating from his operation, and it's much too early to say exactly how he's doing. Actually, I haven't seen him much lately, but on the phone he seems fine -- I'm no doctor, I don't really know, but certainly he sounds good. And as I recall, the last thing he said to me in our last conversation was, "I'll see you in Washington.'"

Despite this reticence, what Martins has to say about related topics tends to suggest that, at the very least, he would not be averse to the idea of transmitting the Balanchine heritage to new generations, or to presiding over the troupe he's served in other capacities for 13 years.

Since he began choreographing five years ago, Martins has created 13 ballets -- a productive record by any standard, and verification that making dances is no longer just a tentative sideline but a major preoccupation for him. Balanchine has been his close mentor -- and a strict taskmaster -- in this as in other aspects of his artistic life. "It's definitely been a learning process," he says. "You cannot be given any tighter restrictions than when Mr. B. hands you a score and says make this into a ballet by June 20. What's hardest isn't putting steps to music -- you can always somehow do that -- but finding a purpose or reason for doing a ballet to this particular score. Sometimes you get a piece of music you're not really wild about and wish you could ignore -- there was that part of "Tricolore," for example, I had to do. I was banging my head against the wall, I just didn't know what to do with it; thank God it's forgotten and out of the repertory.

"Of course, it's wonderful to be given a score by Balanchine, the master -- he's got an uncanny sophistication about what music lends itself to dance. But it's not necessarily your own taste, and I have to find my own connection with the music. I think my sense of this has been growing -- there's music I know might have appealed to me earlier in an immediate way, with lots of melody, that I'd never tackle now because I realize it has no sound structure for dancing. I think I've come a long way, but at the same time it gets more and more difficult to choreograph. Every time I undertake a new ballet, I think what a monumentally improbable task it is. Yes, I expect to begin work on a new ballet soon, probably during the company's season in Washington. The music will be Rossini, Sonatas for String Quartet -- I think."

Juggling his manifold responsibilities has become an increasing dilemma for Martins. "It's tough to find all the time one needs," he says. "ThePennsylvania Ballet advisorship, fortunately, is being handled largely over the phone, though occasionally Ricky [Robert Weiss] and I meet to make decisions. Still, it takes a couple of hours a day, plus watching tapes of ballets, looking at dancers in class, and so on. I expect, though, that as time goes by Ricky will do more and more and I'll do less and less."

Martins' forthcoming book, co-authored by Robert Cornfield, was also a time-consuming project, but an enlightening one as well. "Knowing that this was going to be in print," Martins says, "forced me to rethink my viewpoint on many things -- I realized I couldn't just say what came to mind, that it would have to be something I could stand by. I did have a lot of strong ideas about certain subjects, and a real urge to commit them to paper. There were also some that I didn't," he added in a wry afterthought.

The book (in advance proof form) is engaginly candid and wide-ranging. Martins recounts his early, trying days with the NYC Ballet, days when Balanchine "was devastating to me, and I felt humiliated in front of the whole company," as well as the "turning point" in their relationship after a confrontation. He is unstintingly generous toward other dancers, and insightful about them at the same time. After meeting Mikhail Baryshnikov briefly in the Soviet Union, he saw a film of him doing the "Don Quixote" pas de deux. "... I watched it over and over full of admiration and full of envy. I wanted to be the best dancer in the world, and there on the screen before me was someone better than I was." Later they were to form a fast and abiding friendship. Edward Villella "totally baffled and awed" Martins, "by defying all the rules of everything I had been taught was classical ballet... Here was someone with city street energy, who hadn't been brought up in the tradition-bound, sheltered, directed, somewhat protected environment that I had." As a result, Martins felt himself impelled "to stretch and redefine my conception of dancing." (Villella will be opening the Smithsonian's American Dance Experience series with a special lecture/performance on "The Art of George Balanchine" on Oct. 11, a dark night during the NYC Ballet's run).

Martins is at his most characteristic in writing about the work of making ballets.A sample: "As cliche as it may sound, I think that I am at my most honest when I choreograph. When I talk in public, I want my English to sound more impressive, more extensive than I think it is. When I am in front of an audience there are defensive mannerisms that creep into my personality, and I hide behind a performer's mask. But when I choreograph I search for what is really right, what is the best and clearest and most truthful. I avoid any big applause-getting moments unless they are required, I avoid imposing any extraneous effects, and I get furious when the dancers start acting up in my ballets."

The New York City Ballet performances here -- which will be the first since the Opera House installed the new dance flooring designed by the troupe's own technical expert, Ronald Bates -- will include 10 Washington premieres, a broad sampling of works from the company's 1981 Tchaikovsky Festival and from this year's Stravinsky Centennial Celebration, and other pieces created in the interim since the last Washington appearance. Balanchine, Jerome Robbins, Peter Martins, and John Taras will be the choreographers represented. In all, 15 evening and matinee performances are scheduled -- there's not an unpromising program among them CAPTION: Picture, Peter Martins & Florence Fitzgerald in "Orpheus", photo Copyright (c) Steven Caras