DURING 1975 we celebrated the 75th birthday of Aaron Copland, who has been steadily enlaring his discography as both composer and performer. In September of that year a significant portion of the Berlin Festival was an observance of the 75th anniversary of the birth of Kurt Weill, who died in 1950. Several of Weill's much-discussed but rarely heard works were performed by the London Sinfonietta under David Atherton, with a fine group of English soloists (Mary Thomas and Meriel Dickinson, mezzo-sopranos; Philip Langridge and Ian Partridge, tenors; Benjamin Luxon, bartone; Michael Rippon, bass; Nona Liddell, violin). Immediately afterward, the same aggregation recorded these works in LondonL and the recordings have just been issued in a three-disc Deutsche grammophon set (2709 064) that should gladden a few hearts and constitute a mayor discovery for many listeners.

David Drew, who arranged the festival performances and contributed a charactersically authoritative commentary for the record set, observes that one might view Weill "as an outstanding German composer who somehow lost his voice when he settled in America, or as an outstanding Broadway composer who somehow contrived to write a hit show called The Three-Penny Opera during his otherwise obscure and probably misspent Berlin youth."

Weill was, of course, considered one of the most important creative entities in German music by the time he reached his mid-twenties. He had by then written his First Symphony, a String Quartet and the Violin Concerto, and was starting out on the series of collaborations with Bertolt Brecht, among which Die Dregroschenoper was the most spectacularly successful. The Kleine Dreigroschenmusik Weill extracted from that score is splendidly performed in the new set. Some of the individual playing might suggest a style closer to that might suggest a style cloer to that of the '50s than that of the '20s, but on the whole it is expert, pointed and suitably atmospheric.

Four of the seven works - the Mahagony-Songspie , a Pantomime from the operat Der Protagonist, the Brecht balld Vom Tod Im Wald, and the Berlin Requiem - receive their premiere recordings here. The Violin Concerto had not been available since the retirement of the Gerle/Scherchen version on Westminster and Happy End had not had so authentic a presentation before, despite Lotte Lenya's participation in the earlier version on Columbia.

With the proper assignment of male and female voices, and at the pitch Weill originally specified, Happy End (which Brecht designated "Songs of Hell-Fire and Repentance") is both evocative of its period and remarkably fresh-sounding.Meriel Dickinson's handling of "Surabaya-Johnny" is probably worth the price of the whole set - but then what does one say about the extraordinary chorale "Hossianah Rockefeller" ("Hossianah Rockefeller, Hossiannah Henry Ford, Hosiannah steel and coal and oil, Hosiannah God's own Word, Hosiannah Sex Appeal, etc.")?

The Mahagony-Songspiel , or Kleine Mahagony, is the brief work from which The Rise and Fall of the City of Mahoagny grew, and, for listening without stage action, it is a more effective piece. The original version of the "Alabama Song," with a canonic ending, proves to be a more intriguing concoction than the simplified from used in the larger work.

Vom Tod im Wald (Death in the Forest") and the Berlin Requiem are grim, terse, bitter statements by Brecht, which Weill set for one and three male voices, respectively, with small wind ensemble. Der Protagonist was produced in 1925 with a scenario by George Kaiser; the Pantomime is in the form of a theme, nine variations and cancan finale in which the vocal quartet makes only syllabic gestures.

A good deal more space than is available here would be required for an adequate description of any of the seven works. Let it be said briefly that all of them are fascinating and that the performances could hardly be bettered. The recorded sound is first-rate and the documentation is a treasure in its own right. A most important release, carried off with real distinction.