Londoners and this occasional visitor are at last getting used to that formidable-looking fortress on the Thames' South Bank, the National Theatre of Great Britain. More important, the NT, as its logo goes, is getting used to itself -- its dreams, its realities and its audience.

What is a national theater supposed to be? Because Washington's closest counterpart, the Kennedy Center, has been striving to find its purpose, there could be clues in how NT has progressed since the building's opening in 1976.

One mark of its progress is in its appearance -- the place, after eight years, is beginning to look used. Instead of the gloss of novelty, the building begins to show the patina of experience. Audiences have been getting to know the setup, where the box offices are, the walks across Waterloo Bridge or from the Underground, the cloakrooms, bookstalls, buffets and outdoor terraces, the spaces where strolling players entertain informally before the Main Event.

The Main Event depends on which venue you have chosen: the 1,160-seat, open-stage Olivier; the traditional Lyttleton, which looks far larger than its 980 seats; or the small, rectangular area, the Cottesloe, which seats up to 400 depending on the configuration chosen for a particular work.

The attractions, often as many as 10 or 12 a month playing in repertory, emphasize variety not only from the British tradition but from old French, fin-de-sie cle Scandinavian or new American. Such choices are vitally important to such a theatrical complex.

To better understand all this, one may go directly to a book conspicuously on sale at NT's bookstalls -- "Peter Hall's Diaries." Its 1983 publication, edited from a million words Hall dictated into a tape recorder, caused a sensation that echoes yet.

Hall is the most controversial figure in today's British theater. He succeeded Laurence Olivier as director of the National Theatre Company, officially founded in 1962, and it was under Hall that the building finally opened after successive delays. Previously he had headed the Royal Shakespeare Company at Stratford, instigated its London bases and irritated many by hiring himself out for Glyndebourne and West End efforts.

Publication of his diaries covering 1972 through 1980 may have been a dubious decision; Hall's allusions to some of his associates were dour indeed. But his experiences are certainly illuminating.

To Hall the National Theatre board's courtship of him was ever ambiguous. Olivier's cooperation, so vital, appeared quixotic. The London County Council, responsible for the building's construction, hemmed and hawed over details. Would there even be a Cottesloe? The Arts Council's roles included that of budgeteer. The general contractor for construction and the endless list of minor contractors shared two attributes: they never lived up to their promises either of quality of work or of date of execution. When the company could use the stages was in dispute. Would the queen's schedule accommodate a spring or fall opening? Those who had been so forceful about the dream of a National Theatre became increasingly uncertain whether they wanted any such thing. Backstage crews began work with slowdowns, stoppages, then strikes. The press, initially supportive, became testier and testier as whiffs of gossip escaped from meetings. Media criticism sparked political threats of nonsupport -- a dismal circle.

Through such mitigated or unmitigated disasters, Hall tried to plan how his building was to work once it did open. On this sea of uncertainties he charted several courses; they concern us less than what he accomplished once the strikes and bickerings trailed off.

One notes his choices to turn to the past to find works of value to the contemporary stage, such as Michael Bogdanov's current dramatization of Samuel Taylor Coleridge's 18th-century poem "The Ancient Mariner." Hall himself this season devised a staging for Orwell's "Animal Farm."

Contemporary playwrights are assigned to brush up old works. Most successful this season has been Michael Frayn's adaptation of Chekhov's minor work "Platonov," which he titles "Wild Honey," and which won several of the new Olivier Awards. Frayn here is in quite another mood from his popular farce "Noises Off," and its successor in another mood, "Benefactors."

John Mortimer, currently pleasing Americans with his "Rumpole of the Bailey" teleplays, has a new translation of Feydeau, which was known in the United States as "Hotel Paradiso." Mortimer's title is "A Little House on the Side" and suggests that the Olivier need not be confined to drama or spectacle.

Least successful is Tom Stoppard's variation on Molnar's "The Play's the Thing." Though he transplants the action to a transatlantic liner of the 1920s and allows spots for music, "Rough Crossing" is a rare Stoppard failure.

For Christmas there were traditional mystery plays, "The Nativity," "The Passion" and "Doomsday" for the Cottesloe, which soon reverts to Sam Shepard's "Fool for Love" and David Mamet's "Glengarry Glen Ross." Earlier American holdover hits for the repertory have been "Guys and Dolls" and "Death of a Salesman."

Attention to the past as prologue to the present is what one expects from a national theater, and Hall has been able to attract major dramatists to shed their own glow on what may have seemed murky irrelevance. He has steered the NT into creating its own omnibus collections, "The Romans in Britain" and "The Oresteia," at the same time going actively after such playwrights as Harold Pinter, Alan Ayckbourn and Peter Shaffer for work that often proves commercially popular.

Finally, there are the English classics, as vital to this theater as Molie re and Racine are to the Come'die-Franc,aise.

In a light vein is a production of Goldsmith's "She Stoops to Conquer," designed for visitors to nine cities besides the home stage, according to Parliament's enabling legislation. (Congress gave the same assignment to the Kennedy Center.) This is brightly played by Dora Bryan, the musical favorite, Tom Baker, Michael Beint and Hywel Bennett.

The National's present glory, however, is Ian McKellen as Coriolanus in a superbly clear, involving production of this rarely acted Shakespearean slice of Roman politics.

Again, this focuses a spotlight on Hall in one of his few directorial assignments. It happens that the Olivier "Coriolanus" he staged while heading Stratford 25 years ago has been the criterion against which his McKellen version is judged.

Clarity is its most valuable quality. The conflict between patrician Coriolanus, too proud to knuckle under to the masses, is seen here as the work of media masters who manipulate the plebes, Velutus and Brutus. Hall's staging, centering on a giant gate, draws a slice of the audience around the performers, dressed in modern garb that is sometimes effective and sometimes distracting. But it is McKellen's daring playing of Coriolanus, a mix of soldierly bravado and intellectual perception, that commands our involvement. Rather than ask for our sympathy, he demands our perception.

The production is furthered by the surrounding players: Irene Worth's Volumnia; Greg Hicks as Aufidius; Frederick Treves, as the author's other self, Menenius; David Ryall and James Hayes as the archetypal political manipulators.

There's symbolic truth in the large electric sign on the NT's river side; it advertises the building's performances, exhibits, food, drink and phone numbers. No one venturing near the Thames from St. Paul's to Whitehall can miss the fact that the National Theatre of Great Britain is alive and active.

Symbolically, it's a provocative contrast to the difficulty of finding the Royal Shakespeare Company's London home. This is in the Barbican, an apartment-office-shopping complex erected on land blitzed by the Nazis.

For a generation, the RSC's London stage was in the Aldwych, near Drury Lane, but the Barbican couldn't have been better designed to hide its RSC connections. Even guided by signs from the Underground, you're likely to walk right past the tunnel leading to the three auditoriums. It's also curious that the London homes of Britain's major subsidized theater companies suggest fortresses.

Still, that the National now flashes its welcoming sign along the Thames waterfront and that its gray concrete bulk has assumed a colorful, cozy and stimulating atmosphere for all ranks suggests that the NT is getting accustomed to itself.