FORBIDDEN BROADWAYSatirical revue created, written, and directed by Gerard Alessandrini, with Mary Denise Bentley, Susanne Blakeslee, Herndon Lackey, Jeff Lyons. Brad Ellis, pianist/musical director. EXCEPT for its title, "Forbidden Broadway 1991 1/2" doesn't do anything by halves. The new satirical revue at Theatre East is as sharply and brazenly satirical as its previous editions. Creator-director Gerard Alessandrini scans the theater season just past with an iconoclastic eye and finds ample range for spoofery. From the great and famous to the incidentally silly, Mr. Alessandrini burlesques the current scene to a fare-thee-well. Like any such potpourri, "Forbidden Broadway" has its ups and downs, but here are some favorite moments: Jeff Lyons deserves noting almost any time he appears, so let's just mention his Mandy Patinkin, Jackie Mason, and especially Kim in "Miss Saigon: The Mini-Epic." Mr. Lyons also teams with Susanne Blakeslee in "Just Good Friends" (Adolph Green and Betty Comden). Miss Blakeslee, among other turns, reprises her indestructible Annie for a "Tomorrow is Yesterday" takeoff. Herndon Lackey's contributions in clude an almost unstoppable Topol as Tevye in "If I Sing it Slower." Mary Denise Bentley makes a fetching chandelier ("The Phantom") to Blakeslee's helicopter ("Miss Saigon"), while Lyons "phantomizes" the ubiquitous Andrew Lloyd Webber. Alessandrini salutes the season's flops with "Close a Little Faster," the Tonys with "The Phonys," and the ethnic imbroglio of "Miss Saigon" with an all-out lampoon in which Mr. Lackey's Jonathan Pryce sings, m an Asian Too." Shows may come and shows may go but "Forbidden Broadway" will go on, if not forever, for at least as long as they provide material for Alessandrini's impudent parodies and his willing parodists, not forgetting the accompaniments in this edition of pianist-musical director Brad Ellis. Erika Dyson and Teresa Vuoso respectively deserve a hand for the amusing costumes and wigs that adorn the quick-changing cast of this animated show-biz cartoon.