Donna McKechnie, the Broadway trouper legendary for playing "Cassie" in A Chorus Line, is such a hit in her solo cabaret gig at Arci's Place in Manhattan, to Aug. 11, a return engagement is already planned for Oct. 3-13, a spokesman announced.

An Evening With Donna McKechnie: My Musical Comedy Life (a new title since the original announcement) features songs and stories from the varied career of the 1975 Tony Award-winner, who appeared in such landmark shows as How to Succeed in Business, Promises, Promises and Company. This is her first cabaret appearance since 1987, although she has been developing a theatre version of this Evening called Inside the Music. Thommie Walsh (her fellow Chorus Line performer) directs. Musical director Phillip Fortenberry is on piano. McKechnie previewed her act at Arci's for one night in June and returned for this longer run July 24. Tickets are still available for the run to Aug. 11, but fans, media and industry folk have been crowding in.

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McKechnie, who was seen in Broadway's State Fair and Paper Mill's Follies, will soon star in an intriguing theatrical footnote: She'll play Lola in a musical version of Come Back, Little Sheba, called Sheba, Aug. 31-Sept. 2 at the White Barn Theatre in Westport, CT. The show closed out of town in the 1970s. The original Ralph Burns orchestrations were unearthed and the full production at White Barn plays only four performances. Lee Goldsmith wrote book and lyrics, Clint Ballard wrote the score.

An Evening With Donna McKechnie performances are 9 PM Tuesday, 8:30 PM and 11 PM Friday-Saturday. Tickets are $30 with a $15 food-drink minimum. Arci's is at 450 Park Avenue South between 30th and 31st Streets. For information or reservations, call (212) 532-4370. — By Kenneth Jones