Capsule comments on current stage productions: BANJO DANCING -- (Arena's Old Vat). Administrations come and go, but Stephen Wade may well be here forever. In this indestructible one- man show, he plays the banjo, tells some tall tales, demonstrates the noisy art of clog dancing, and in the process makes friends with just about everyone in the audience. GHOSTS -- (Eisenhower Theater, Kennedy Center). Henrik Ibsen's play about the awful consequences of sweeping truth under the rug of convention is not quite the shocker it was a century ago. But there's still absorbing drama here, even if this production has troubles pinpointing it. As Mrs. Alving, widow of a degenerate captain and mother of a syphilitic son, Liv Ullmann is as mesmerizing on stage as she is on the screen. But, given a largely second-rate supporting cast, she often appears to be up there all on her own. Through August 14. THE NEW IMPROVED BRIDE OF SIROCCO -- (New Playwrights' Theater). This-grab bag of new and old sketches and songs from the antic pen of Tim Grundmann can be as nutty as a fruitcake. But, like fruitcake, it also has a tendency to crumble. Some of Grundmann's daffy notions: the saga of Tarzan and Jane, as Puccini might have written it; the selection of the Pope, as if it were the Miss America contest; and the life of Peter Mark Roget, the thesaurus-maker, as a would-be Masterpiece Theatre presentation. The five-member cast is uneven, but Yeardley Smith, an actress who looks like a mushroom with a button nose, triumphs in numbers good and not-so-good. Through August 15. JAY O'CALLAHAN -- (Round House). Telling stories born of his travels and his imagination, O'Callahan turns the theater into a big campfire, and adults into rapt children, in this unusual one-man show. He has a different voice and posture for each of his characters, but it's mostly his ability to convince an audience that his tales are unfolding for the first time ever that makes for the evening's delight. The current batch of stories are on the theme of "Summer Madness." Through August 8. SONGBOOK -- (Olney). A silly spoof of those black- tie tributes show folk are always throwing for themselves, this British revue pays homage to an imaginary British composer named Moony Shapiro and the tunes he wrote over five decades. The satire is fairly benign and for the most part the performances are never more than routinely pleasant. The only moments of real spunk are provided by Anthony Risoli, as Moony Shapiro himself, an ingratiating opportunist who looks on each of life's tribulations as the cue for yet another song. Through August 8. THEY'RE PLAYING OUR SONG -- (Warner Theatre) Flaky lyricist meets and eventually wins neurotic composer in this ho-hum musical by Neil Simon (book), Marvin Hamlisch (music) and Carole Bayer Sager (lyrics). Hamlisch and Sager also served as the real-life models on which the slender tale is hung, but surely theirs was a far more gripping relationship than this. Repeating her original Broadway role, Lucie Arnaz brings a lot of heart to the stage, not to mention a clocksure sense of comic timing. As the other half of the romantic equation, Laurence Luckinbill wades boldly into the musical comedy waters and drowns. Through August 8.