The title of Tim Grundmann's comedy revue at New Playwrights' Theater _ "The New Improved Bride of Sirocco (or the Texas Chain-Saw Musical)" _ holds much zany promise, but the show delivers only flashes of fun.

Too often the material has a hoary feel of Firesign Theater, sketches drag on to no good purpose, and some of Grundmann's jokes aren't worthy of him. It seems that a fresh, funny show is trying to wriggle forth from something fat and overripe.

That the struggle ends badly is a shame. The actors and the musicians (including Grundmann at the keyboard) bring to the production so much high energy -- much of the time, they're dripping sweat -- that they almost pull it off.

"Il Tarzani," a treatment of the Tarzan- and-Jane saga as Italian opera, points up what's right, and also what's wrong, with the whole show. Grand opera in the jungle is a lovely idea, and Steven LeBlanc in the title role, as well as Caron Tate as Jane and Yeardley Smith as Cheetah, plumb it for all the laughs they can. The spectacle of Tarzan and Jane singing mock-Puccini duets in pidgin Italian, while Cheetah clings to the jungle lord and makes monkey noises, is just plain funny.

Some of the other material is not, however, such as an intermission interview with the leading lady, a Broadway-like show tune, a bump-and-grind number and too much pidgin Italian.

Grundmann often starts with the unexpected and original, and weighs it down with the extraneous and predictable. Occasionally some talent shines through. THE NEW IMPROVED BRIDE OF SIROCCO -- At New Playwrights' Theater, 1742 Church Street NW, through August 15. 232-1122.with photo.