Followers of musical-theater oddities and 18th-century British comedy will be especially attracted to this amusing but little-known adaptation of Henry Melding's 1732 Rape Upon Rape, or The Justice Caught in His Own Trap. But cultish and historical appeals aside, Melding's sardonic satire of sex, law, politics, and the media is timely: it's the story of Mr. Squeezum, a lying and lecherous jurist, and proper Hilaret Politic, who tries to expose Squeezum as a sexual harasser only to find herself smeared and manipulated by chaotic public hearings and a rumor-mongering press. Created in 1959 as the debut production of London's Mermaid Theatre, the show helped stimulate a renewed interest in Fielding that crested in the 1963 movie Tom Jones. Its diverting score was written by lyricist Lionel Bart (who went on to pen Oliver!) and composer Laurie Johnson (whose buoyant, harpsichord-motored blending of Baroque and jazz-pop styles anticipates his well-known theme music for TV's The Avengers). Mermaid's founder-director Bernard Miles (who later was granted a lordship by Queen Elizabeth, making him Britain's only theatrical figure besides Laurence Olivier to be so honored) devised the script. This veddy English show is rarely produced in America; it's being offered in a high-spirited, fairly professional performance by DePaul University theater and music students under the able guidance of director-choreographer Betsy Hamilton and conductor Mark Elliott. The performers are attractive, talented, and disciplined, and their youth suits the boisterous material just fine. The Theatre School, DePaul University, October 31 through November 10 (Blackstone Theatre, 60 E. Balbo, 362-8455). Wednesdays-Saturdays, 7:30 PM; Sundays, 2 PM; Thursday, November 7, 10 AM. $5-$7.50.