The mansion has landed.

Although the advance hype has been deafening and the backstage machinations have frequently threatened to eclipse those onstage, "Sunset Boulevard," Andrew Lloyd Webber's lurid new musical and extravaganza, officially took over the Minskoff Theater on Broadway last night.

When it is good, it is outlandishly good. When it isn't, it is big. Both observations may be of secondary importance, however, since the musical allows Glenn Close to give one of those legendary performances people will be talking about years from now. As the film star Norma Desmond, a turbaned relic who considers herself the idol of millions, the actress takes breathtaking risks, venturing so far out on a limb at times that you fear it will snap. It doesn't.

The portrayal, as stylized in its way as the demon in a Kabuki play, is shrewd and hugely manipulative. Norma Desmond was not a luminary of the silent screen for nothing, and Ms. Close is not one of our finest actresses on instinct alone. They are a transfixing pair.

Whenever Ms. Close is offstage, in fact, "Sunset Boulevard' loses much of the macabre originality that makes it a companion piece to "The Phantom of the Opera." Mr. Lloyd Webber and the director, Trevor Nunn, are no fools, though. The mundane patches are nester permitted to last too long before a surge of melody or a stunning stage effect lifts the musical out of the commonplace and sets it back on its fateful course through the palm-fringed Hollywood night.

It is, after all, a dark and venomous tale that Don Black and Christopher Hampton are telling. Closely modeled on Billy Wilder's 1950 film, "Sunset Boulevard" charts the relationship between Joe Gillis (Alan Campbell), an out-of-work screenwriter looking to rustle up a buck or two, and the forgotten star who sees him rejuvenating not only her career, but also her love life. If she's a spider, he's a leech. Both are opportunists and thrive on blood. There's no surprise in how this garish mating dance ends, since the very first of the amazing sights engineered by Mr. Nunn, John Napier, the set designer, and Andrew Bridge, the lighting designer, is that of Gillis's dead body floating face down in a murky swimming pool. What makes it amazing is that we're looking up at the corpse, viewing the splayed and waterlogged limbs from the vantage point of the drain. That, it turns out, is the perspective of the musical as a whole: the underbelly of Hollywood is to be poked, prodded and exposed.

Even Norma Desmond's palazzo, the second takeyour-breath-away sight of the evening, is a nightmarish monument to claustrophobia and gilt. its most prominent feature, if you exclude the forbidding pipe organ, is a majestic staircase that Ms. Close is constantly ascending and descending. Ever since Ziegfeld, stars and staircases have gone together, of course, but Ms. Close brilliantly uses each sweeping entrance and imperious exit to illuminate a deluded psyche. At the end, when Norma slithers down the stairs as Salome, posturing grotesquely in what is meant to be a sinuous dance of seduction, the transformation is complete. Ms. Close is by this point quite literally out of this world — a supremely ridiculous, unbearably pathetic monster.

Mr. Lloyd Webber's score is full of rich and swelling melodies, although the charge brought against the composer in years past holds true: when he latches onto an insinuating musical theme, there seems to be no such thing as one reprise too many. Norma's arrogant boast, "We gave the world/ New ways to dream," pops up all over the place. "Too Much in Love to Care," however, proves a glorious duet for Joe and Betty Schaefer (Alice Ripley), the pretty young screenwriter who awakens Norma's jealousy and what's left of Joe's integrity.

The musical's two big songs, "With One Look" and "As if we Never Said Goodbye," are Norma's, even if Barbra Streisand has already staked her claim to them. Ms. Close does not sing them so much as cast a spell over them. Her voice is small and unexceptional. The amplification comes from her acting skills: the flashing eyes, the magnanimous stance, the histrionic gestures actually give the notes color and power

"As If we Never Said Goodbye" marks Norma's return to the studio where she enjoyed her long-ago triumphs. Separated from lesser mortals by a blinding spotlight, Ms. Close arches her neck and shows us the fabled, larger-than-life goddess Norma used to be. The ferocity of the character's will and the depth of her folly are never more apparent.

The lyrics by Mr. Hampton and Mr. Black tend to the pedestrian or labored, when Ms Close is not working her magic on them. "Let's Have Lunch," the opening number delivered by the extras and hopefuls who aspire one day to conquer the mount, Paramount, is a compendium of cliches, not all intentional. So is "This Time Next Year," in which they express their New Year's Eve wishes for success, or at least a walk-on part, in the months to come. "Sunset Boulevard" is very adroit at covering up its weaknesses, though.

That youthful wish-making is just half of the scene. Norma is also celebrating New Year's in her fashion, alone in the splendor of her mansion, with only a sorry band playing tangos to keep her spirits up. Moreover, that's all we see, at first. Then the mansion slowly rises off the stage to reveal, underneath, a cramped Hollywood apartment bursting with bodies having a raucous good time. The split picture is extraordinary. Helicopters taking off and setting down are beginning to look like child's play these days.

Mr. Wilder's movie may have been a small-screen black-and-white affair. This is very much a VistaVision musical, although Mr. Napier has drawn the line at Technicolor. His designs favor somber shades of gray, green and brown. The costumier, Anthony Powell, keeps his sense of profligacy in check until it comes time for Ms. Close to make an appearance. Then he pulls out the leopard prints, the zebra stripes and bugle beads by the bucketful. Showmanship is very much the guiding principle here, from Bob Avian's aggressive musical staging to the lush orchestrations by Mr. Lloyd Webber and David Cullen.

"Sunset Boulevard" certainly has no hidden depths, no secrets, no ambiguities. The film can claim a more highly developed sense of irony and a far sharper comic tone. Whether we like it or not, machinery and the voracious public appetite for spectacle are remaking the contemporary musical (Even Norma's gleaming motor car, a 1931 Isotta Fraschini, earns entrance applause.) What you see on the stage of the Minskoff turns out to be pretty much all you get. But I suspect only the most blasé theatergoers will feel shortchanged.

As Gillis, Mr. Campbell Is-appealingly boyish with a shock of blond hair and a suggestion of dimples to indicate that he has not completely relinquished his innocence. Could he afford to be even more of a cad? Probably. Still, he has a strong stage presence and he tears into the title song with its idiotic lyrics ("Sunset Boulevard/ Headline boulevard . . . Sunset Boulevard/ Jackpot boulevard") as if it really were a scathing indictment of movieland. Ms. Ripley may be playing a cliche role, the starry-eyed ingenue with ideals, but the performance is remarkably cliche-free. The third standout, although he spends a lot of time hovering in the shadows and lurking under archways, is George Hearn, who makes Max von Mayerling, Norma's butler, a mixture of menace, mystery and ever-so-discreet gallantry. Mr. Hearn is granted just one song of his own, a paean to Norma entitled "The Greatest Star of All"; you'll wish he had more.