ON JANUARY 29, 1728, playwright and poet John Gay shocked the London operatic world with a blockbuster called "The Beggar's Opera" that overturned all the established standards in that opera-happy town. It was sung in English at a time when Italian was considered the only language for opera; it featured simple tunes (pop hits of the day and folk melodies) rather than the elaborate da capo arias then in vogue, and the leading characters were the scum of the earth -- pimps, highwaymen and beggars -- who struck the same kind of heroic poses as the Greco-Roman gods and warriors of opera seria.

It was a wild success. Opera staggered from the blow but recovered. Ironically, Gay's producer, John Rich, used the profits from this anti-opera to build the Covent Garden Opera House, one of the world's great shrines of opera in the grand manner.

Almost exactly two centuries later, on August 31, 1928, composer Kurt Weill and playwright Bertolt Brecht brought out an updated revision of John Gay's opus. They moved the time and locale to Victorian London, spiced up the lyrics with a message of social protest and general misanthropy, gave it a new, energetic, jazz-flavored score and renewed the attack not only on opera but on the social snobbism associated with it. Again, it was a smash hit.

This weekend and next, at the Barns of Wolf Trap, the Prince George's Civic Opera is bringing back both of these anti-operas, running them on alternate evenings. Most of the cast will be singing the same roles in the two productions. Both works are distinctive landmarks of musical theater and both have been effectively performed already at what amount to out-of-town tryouts in Prince George's County.

No complete recording of "The Beggar's Opera" is currently available, but some of its songs can be heard on LP (Harmonia Mundi 1071). The Threepenny Opera has been recorded many times, and only one of the recordings (Vanguard S-273E) is really bad -- much too operatic for this anti-operatic music. The old Theatre de Lys production, which ran for many years off Broadway, can be heard, digitally remastered, on a Polydor recording (820260-1E). It uses the brilliant Marc Blitzstein translation, which is partly familiar to millions who have heard pop recordings of "Mack the Knife," the hit tune of the show. The New York Shakespeare Festival Production, which uses the somewhat more literary Ralph Mannheim translation, can be heard on CBS PS 34326.

But the definitive performance, for those who are not put off by language barriers, is the stylistically perfect one done in German in the '50s, starring Lotte Lenya (CBS M2-37862, 2 LPs).

THE BEGGAR'S OPERA -- The Barns of Wolf Trap, 8 p.m., Saturday and April 25.

THE THREEPENNY OPERA -- The Barns of Wolf Trap, 8 p.m., Friday and April 24 and 26. On records: "Die Dreigroschenoper" (CBS M2-37682, 2 LPs).