Never, like ever, is a dangerous word, but never, in a half-century of playgoing, have I heard or seen anyN thing like what happens these nights in 45th Street's Plymouth Theater.

The phenomenon occurs around 11:30 after a performance, which has started at 2 in the afternoon, the spectacle people are nicknaming "Nick-Nick," the Royal Shakespeare Company's inspiration from Charles Dickens' "Nicholas Nickleby."

There are prolonged cheers, risings and wavings from the house to which, as if shocked back into being themselves again after hours of being other people, the cast responds with dazed faces, tentative hand-clapping and finally jubilant waves to those blurred faces beyond the lights.

The breath-taking $100 it costs to see the two-part production does not, by itself, account for these responses. And the amount is not so astounding when considered along with the length of the play. Someone has figured out that a 70-minute off-Broadway musical costs its viewer 23 cents a minute and that this marathon costs, by the hourglass, only 20 cents a minute. For all the startling sums, including a potential weekly gross of $396,000, the three American importing firms for the company are bound to wind up losing a packet come January 3.

I suspect that "Nick-Nick" so far is not selling out all those $100 tickets. But no seats are unoccupied; familiar, lean faces are clearly guests of the management, drama students, Equity members and the theater's hundreds of anonymous supernumeraries. The cost of transporting the company, staff and props from England, paying wages and per diem, totals about $5 million for the 14-week visit.

Why, you ask yourself, are the Shubert Organization, the James Nederlander firm, Elizabeth McCann and Nelle Nugent taking on so likely a loss?

Are they trying to show us how exciting theater can be? Are they pointing out that our own theater is relatively thin gruel? Could this be altruism?

These thoughts occurred after I asked myself whether an American company could have pulled off such a production. There is not, in our fabulously rich country, a theatrical organization which could have come close to it.

One can regret this but should not be surprised. The reason lies in the differences between the two countries, our own impatient wastefulness and the long theatrical culture not only of Britain but of the European continent. There is a disciplined richness of texture here lacking in both our theater and, it often seems, our nation.

The Dickens dramatization has the prime quality of theater out of style in our navel-gazing era: narrative drive.

We watch not just the rise of a young man, his widowed mother and genteel sister, but his recognition that life is perpetual struggle to assert right over wrong. Something always is happening to forward his story and, though much is teasing melodrama, its driving narrative is its driving force. A story is told. We are not watching characters analyzing themselves.

The company's collaborative staging concludes the story in a way Dickens did not contribute, a circular ending in which still another orphaned waif, not unlike the luckless Smike, will begin life with the cards stacked against him.

This concept, rather like a round in song, welds finale back into the first scene, an ingenious inspiration. One emerges thinking of the dark side of early Victorian England, the drawings of Dore', the books of Engels, Carlyle, Bartlett and Baker, which contributed so much to Kellow Chesney's "The Anti-Society," that picture of the Victorian underworld published here in 1970.

Visually, this atmosphere flows from a me'lange of crafts, the costumers' grays and blacks, the lighting designers' pinpoints and cold shafts, and, sometimes, full-stage pinks, stagecoaches and walls formed by the players' bodies, mimed in the traditions of 18th-century Italy and 20th-century France.

Aurally, 13 musicians and a company able to sing either beautifully or lustily as the assignments demand, convey the sense of time and spirit conjured by composer-lyricist Stephen Oliver, If a bird song is needed, vocal chords supply it. For this also is a full-scale musical.

In form, the staging suggests the organics of Meyerhold, the alienation of Brecht. Ramps, crosswalks, trailing ropes, visible lights, ladders, slopes and steps can become anything the company wishes to suggest. It forces us to imagine.

Not a blink of time is permitted between contrasting or even unrelated episodes. On occasion characters of interweaving stories can be seen together, invisible to each other. The sense of several things happening at once, pioneered by D.W. Griffith in "The Great Train Robbery" and so vital to film, is used here with ingenious, living e'lan.

There is ensemble sensibility, adults playing children, women acting men, men miming women. There is a quickening when one recognizes that one of the players has been limning several vastly different cameos; one actress (Suzanne Bertish) rings three variations on women who never will snag their men. When the playmaking Crummles family comes on for the final hour of Part I, there is a wholly different style of acting, satire on 19th-century theater customs, the broadness which so captivated Dickens himself.

This is the kind of character-acting our film makers seem always to miss in minor casting through the geographical fact that films are made 3,000 miles from our theater capital. In London, players may act for films during the day, on stage at night, a minor role in one, a major one in the other.

Our American stage has had a lusty, much-traveled history, but our audiences do not have Europe's long theatrical tradition. A kind of snobbery has overtaken our theatergoers, whereas England's, despite those tea-guzzling intervals, are keen connoisseurs from all ranks.

Nor, of course, do we have the subsidized theater of Europe. While the RSC, the National, the Royal Court and other tax-financed groups plough ahead, our theater is supposed to pay for itself.

Nor have we developed quite the same literary tradition of sagas, those complex, many-peopled, rambling yarns of the Greeks, the Germans, the Italians, the Russians and the French, the chronicles of such as Shakespeare, Scott or Thackeray. After 19th-century similarities, our 20th-century critics increasingly have favored narrower canvasses, however much the public may go for splashier, less finely written works.

And the long vogue of method acting hasn't really stretched our general run of players, who've been known to complain that "you didn't get what I was thinking." The art of acting consists of externalizing the internal.

Thus, national traditions and the royal emoluments which subsidized the performing arts led to this acting company peopled by players of uncommonly varied experience. David Threlfall's meticulously realized Smike, Edward Petherbridge's precise Newman Noggs, Christopher Benjamin's genial humanity for Crummles, Lila Kaye's flashy bounce for Mrs. Squeers and Mrs. Crummles all follow scores, perhaps hundreds, of earlier roles. That Rose Hill can find so sweet a pianissimo for her old lady aria lies in the fact that 40 years ago she was an opera singer. After 14 years in lesser RSC parts, Roger Rees shoulders the title part with superb, striking self-discipline.

Will you be aware that this is a pretty long sit? I was at the start of both parts, being a cautious type, though others have complained, more tellingly perhaps, that they were in the latter portions. Whatever, there are three intervals as well as the dinner break. What if your $100 winds you up in the last, top row? That won't matter much, for it's a small house. How about those accents of York, Wales or Cockney? While these are being softened, Masterpiece Theater takes a bit of getting into, too. How can you afford $100 on top of the New York jaunt? Try bus, $47.75 round trip.

"Nick-Nick" is one of the theater events of the decade, its nightly ovations enviable and deserved, and I'm grateful those Broadway commercial producers decided to educate us as to what we're missing.