It’s become a sad truism that the only thing remotely funny about the tattered condition of the Broadway musical is Gerard Alessandrini’s annual skewering of it. Twenty years ago, Forbidden Broadway was something of a cult item prized largely by theatre mavens and Broadway queens (often one and the same); now it’s an institution. Unlike most hardy perennials, however, Alessandrini’s remains true to its soul — however mean that particular spirit is taken to be.

Actually, it’s fairly benign; satire this sharp has to derive from some pretty strong emotions. True, the John Freedson and Harriet Yellin’s presentation of Forbidden Broadway: 20th Anniversary Celebration, presented as part of Off-Broadway Series South, directs its curare-tipped barbs at the usual Broadway suspects: the monstrous egos of stars (Mandy Patinkin, Kathleen Turner, Michael Crawford), the over-produced pabulum that passes for big musical statements (The Lion King, Miss Saigon, Les Misérables). And while most of the show is wickedly observed and wildly funny, there’s a frisson of rue behind the jokes — where are the enduring stars today? the important young songwriters? the great new shows? is that all there is? When Alessandrini sends up the revival of Chicago (“Glossy Fosse ‘Em”), he’s satirizing neither the show itself nor Bob Fosse but the way the choreographer’s idiosyncratic style is pressed into gussying-up what is essentially a glorified concert.

This edition of Forbidden Broadway includes material limned from the show’s two-decade history. As a result, not everything in it is fresh — Cats has passed its ninth life, Carol Channing no longer threatens yet another stab at Dolly Levi, and a 1990s dig at Julie Andrews’ decreasing vocal range feels rather cruel now that even that has been taken from her — but almost all of it is still funny.

There’s the justly famous “Chita, Not Rita” bitch-fest between Rivera and Moreno; and the piercingly apt “SuperFranticHyperActiveSelfIndulgentMandy,” whose mantra (“These are songs rich in tradition, and I have brought them here tonight … to pummel them to death”) Patinkin himself applies with equal fervor to everything from Sondheim to Judaica. Indeed, my only cavil with this perfect gem of burlesque is that it may not go far enough; but then, how do you parody what’s already self-parody?

Best of all, arguably, is “Mucous of the Night,” in which the shade of Ethel Merman hectors a ridiculously reverbed Michael Crawford to the tune of “You’re Just in Love” (“I keep singing/’Though my voice is air …”), which may be the single finest, and most well-deserved, critique of Crawford’s astonishing vocal thinness ever written. (Even more flabbergasting is the vast public — only slightly smaller than Patinkin’s — that transparent gruel of a voice commands.) When La Merm says, after Gloria Swanson, “They had voices then,” we can only wish they’d reincarnate.

Alessandrini’s newer material includes such delights as his costume designer Alvin Colt’s riffs on The Lion King; an uproarious commentary on the fabled Disney miserliness, even unto keeping its own hit machines going (“Beauty’s Been Decreased”); and a number of other darts equally well-aimed at the House of Mouse. Miss Saigon takes appropriate heat for its greeting-card lyrics, numbing volume, and ludicrous helicopter effect. A buck-toothed Sarah Brightman nearly shatters our own teeth with her over-amplified top notes. And the turn-table in Les Misérables becomes practically an entire second act.

The quartet of mummers currently at play in the A.J. Fletcher Opera Theater is sublime. Eric Gutman is marvelously glib as everyone from Crawford to Alan Cumming, while Mark-David Kaplan is equally risible as a befuddled (Victor) Hugonaut and a self-adoring Mandy complete with squeezed high notes. But it’s the women who walk off with the evening’s honors.

Heather Ayers pulls off a flawless Bebe Neuwirth, a terrifyingly toothsome Channing, a deliciously sultry Moreno, a pitch-perfect Andrews, an hilariously pitiable Belle, an astonishing Streisand sans recourse to prosthetic rhinoplasty, and a Brightman so eerily like the real thing you almost look away in embarrassment.

The show’s crowning (clowning?) glory, however, is Kristin Zbornik. This protean comic gives us a blasé, cigarette-smoking Annie Warbucks in a scarlet jump-suit (“I’m 30 years old/Tomorrow…”) one moment, and a superannuated Kathleen Turner practicing her patented hair-swing the next. Her Liza Minnelli, meanwhile, all tics and nervous giggles, is second only to her Merman, which I rate as one of the damnedest transformations ever seen.

This is not mere mimicry, or even acting. After all, anyone with enough imagination and good diaphragm control can parody Merman’s outsize manner and brassy, swooping style. What Zbornik does is something rather more like channeling, or simply being. For a few exhilarating minutes you forget that what you’re watching is not the original. Which may just make you wish the old girl had never gone away in the first place.

That’s more than satire — it’s practically wistful. When was the last time “Saturday Night Live” put a lump in your throat?

Off-Broadway Series South presents Forbidden Broadway: 20th Anniversary Celebration Thursday-Friday, Jan 16-17, at 8 p.m.; Saturday, Jan. 18, at 2 and 8 p.m.; and Sunday, Jan. 19, at 2 and 7 p.m. in the A.J. Fletcher Opera Theater in the BTI Center for the Performing Arts, 2 E. South St., Raleigh, North Carolina. $31-$43. 919/834-4000 or 919/231-4575 (discounts for groups of 20 or more). [inactive 4/04] or [inactive 1/04].