I would guess that not even her most loyal fans think of Judy Roberts as a prairie pioneer, but the notion works for me. In the early 70s she established the Chicago model of a working woman bandleader, and half a dozen jazzwomen have solicited her support and advice since (though none of them went on to include Chicago ballplayers in their performances–as Roberts did with the immortal Carmen Fanzone, who played trumpet about as well as he played third base at Wrigley). Her good heart aside, Roberts wouldn’t have earned the respect of these acolytes without the lively enthusiasm she brings to the piano, buttressed by a sparkling technical command of the keyboard, and her sly musical wit: when Roberts makes a musical joke, it sneaks up from within the music instead of landing on top of it. Her voice has lost some of the syrup that always threatened to clot her ballads, but remains sweet and flexible; occasionally, at its least demonstrative, it becomes a soft cushion for unspoken emotions. Roberts often finds herself stereotyped as a lounge act–partly, I suppose, because most of her performing occurs in lounges–and certainly her music occasionally echoes that made-to-order sincerity that prevents music lovers from taking most lounge performers seriously. But with Roberts, that’s the exception and not the rule; and the chance to hear her in the city’s most storied and respected jazz club should help prove that point. For this engagement, Roberts’s band features the dependable bassist Stewart Miller; Greg Sergo, whose drumming alternately floats and stings; and the excellent if lesser-known saxophonist Greg Fishman. All of them appear on her recently issued CD Circle of Friends. Roberts produced and released this album on her own, and it represents the range of her musical interests better than anything else she’s recorded. Friday and Saturday, 9 and 11 PM, and Sunday, 4, 8, and 10 PM, Jazz Showcase, 59 W. Grand; 670-2473.