AT D.C. SPACE, "Betty Inside/Out" is a flaky, funny evening of sisterly silliness and self-indulgence "conceived, written, directed, produced by and starring" the (mostly) a cappella singing group called Betty. Formerly known as On Beyond Zebra, the trio was formed by Dupont Circle characters -- and hometown rock stars -- Amy and Bitzi Ziff and Alyson Palmer.

The first act casually introduces us to the three Bettys with a (very) loosely constructed hey-let's-put-on-a-show playlet punctuated by original songs and outre' poems.

There's Amy, the amusingly egocentric leader, who is also a standup comic and cellist; twin sister and keyboard player Bitzi, Amy's earthier, exasperated foil; and stunning, statuesque Alyson, who sings in a dusky alto and plays a mean finger-popping bass. All three are naturally charismatic performers, and much of their material is quite funny, though some is so embryonic and insular as to be bewildering.

Once everyone is acquainted, the stage is set for act two, a typical Betty concert in which the three exude a combination of glamor and goofiness, embellishing their looney tunes with intricate, inventive vocal interplay.

Winning numbers include "Fed Up," a pointed number about a destructive obsession with slenderness; a breakup song called "Go Ahead and Split, Mr. Amoeba Man"; a scat rendition of Lewis Carroll's " 'Twas brillig and the slithy toves . . . "; and the show stealer, the theme from the "Petticoat Junction" TV series transformed into a slow, spacey blues -- you have to hear it to believe it.

BETTY: INSIDE OUT -- At D.C. Space Wednesdays and Thursdays through May.