ANYONE WHO KEEPS UP with recordings must have noticed that 1978 has been a very good year. In addition to an abundance of exceptionally attractive releases -- of both new material and reissues -- there have been significant developments in the recording media themselves. Cassettes are more prominent than ever, with a heartening level of quality prevailing. Open-reel tape has come back: Barclay-Crocker now has a sizeable catalogue of reels from several labels, some processed by B-C itself. Perhaps the most exciting development on the technical front -- more than the direct-to-disc recordings introduced in the last few years -- is the phenomenon of digital recording, especially as manifest in the beautifully processed Denon series from Nippon Columbia.

As for specific releases, there have been more than a few this year which will surely establish themselves as classics in the annals of recorded music. While the Schubert year yielded perhaps less than we might have expected (perhaps the sesquicentennial of a composer's death isn't that effective a gimmick), there were five recordings of four of that composer's chamber music masterworks which constitute a more than adequate memorial in terms of the deep pleasure they provide. The Quartetto Italiano's impassioned realization of the last and greatest of Schubert's string quartets, No. 15 in G major (Philips 9500.409; cassette 7300.617), may well be the finest performance this group has given us in its more than 30 years of distinguished activity. Superlatives can be exhausted, too, over the recording of the String Quintet in C major by the Melos Quartet of Stuttgart with Mstislav Rostropovich as second cellist (Deutsche Grammophon 2530.980; cassette 3300.980). Alfred Brendel, with bassist James van Demark and members of the Cleveland Quartet, has recorded an especially joyous performance of the Trout Quintet (Philips 9500.442). The Academy of St. Martin-in-the-Fields' Chamber Ensemble introduced itself with a radiant account of the Octet in F (Philips 9500.400), and the New Vienna Octet offered one just as attractive (with some repeats omitted by the English group) for less than half the Philips price on London STS-15346.

A new Quintetto Boccherini has begun what promises to be an outstanding series of the eponymous composer's cello quintets, with an initial disc that includes the famous Musica notturna delle strade di Madrid (HNH 4048); the first installment in the Tokyo Quartet's Bartok cycle, comprising Quartets Nos. 2 and 6, carries a similar promise. The Tatrai Quartet, continuing its unhurried survey of Haydn's string quartets, has said all that needs saying on the subject of the Op. 64 set (Hungaroton SLPX-11838/40). The Fitzwilliam Quartet, whose Washington debut went all but unnoticed two months ago, continued its Shostakovich cycle with beautiful performances of Nos. 4 and 12 on L'Oiseau-Lyre DSLO-23, Nos. 3 and 11 on DSLO-28. Also from England, the Gabrieli Quartet's exalted realizations of Dvorak's Opp. 51 and 105 came as a bargain on London STS-15399.

Chamber music accounts for most of the interest among Denon's releases so far, with the Smetana Quartet out front in works of Mozart (the string quintets K. 515 and 516 with Josef Suk as first violist on OX-7089-ND, the six "Haydn" quartets on 7008, 7034 and 7039), Smetana (the two quartets, 7049), Janacek (two quartets, 7066) and Beethoven (Op. 18, Nos. 1, 2, 4 and 5, on 7077 and 7105). The Suk Trio is remaking much of its repertoire, with an irresistible Dvorak Op. 65 on 7122 and a majestic new Archduke on 7035, but this group's earlier Archduke, newly reissued on Quintessence (PMC-7082, cassette P4C-7082), is not only much less expensive, but a bit more persuasive, possibly the most "basic" item in the chamber music discography.

Raymond Leppard's inspiriting performances of Handel's three concerti a due cori with the English Chamber Orchestra, beautifully (if nondigitally) recorded on Philips Festivo 6570.114 (cassette 7310.114), are sheer perfection and sheer delight -- just the treatment these marvelous works have been wanting. The same may be said of Kurt Malzer's Vanguard set of the five Mendelssohn symphonies (VCS-10133-34), especially impressive on open-reel tape (Z 10133).

Klaus Tennstedt's U.S. disc debut as conductor of the London Philharmonic in the Mahler First (Angel S-37508) really does seem to be the definitive version of that much-recorded work, and Claudio Abbado just as surely sweeps the field with his magnificent new Mahler Fourth with the Vienna Philharmonic (and mezzo Frederica von Stade, DG 2530.966; cassette 3300.966). Eugen Jochum's luminous reading of Das Lied von der Erde, with Nan Merriman, Ernst Haefliger and the Concertgebouw Orchestra, one of the most effective on records, is welcome back in DG's Privilege series (2535.184; cassette 3335.184), and Igor Markevitch's towering performance of Tchaikovsky's Sixth Symphony, the Pathetique, is an even more welcome reissue on Philip's Festivo label (6570.047; cassette 7310.047).

Another Tchaikovsky conductor to be reckoned with, it appears, is Vladimir Ashkenazy, whose new recording of the Manfred Symphony (London CS-7075) is the most persuasive treatment that work has ever received on records. In other Russian material, Leonard Slatkin, with the Saint Louis Symphony Orchestra, works a miracle with Rachmaninoff's First Symphony (Candide QCE-31099) and, with the stunning mezzo Claudine Carlson and a good chorus, gives us one of the truly memorable versions of Prokofiev's Alexander Nevsky (31098).

Leonard Bernstein's most exciting release for 1978, for this listener, was his magnificent performance, as both soloist and conductor of the Israel Philharmonic, of Mozart's Piano Concerto No. 25 in C, with an especially imaginative cadenza of his own; as filler Bernstein conducts the New York Philharmonic strings in Eine kleine Nachtmusik (Columbia M 34574).

Emanuel Ax's first concerto recording, the Chopin F-minor with Ormandy, is a surpassingly poetic realization (RCA Arll-2868; cassette ARK1-2868). Maurizio Pollini's set of Beethoven's last five piano sonatas is an aristocratic blend of technique, insight and overall elegance (DG 2709.072; cassettes 3371.033). Krystian Zimerman is crisp, fresh and irresistible in Mozart's Piano Sonatas K. 280, 281, 311 and 330 (DG 2531.052; cassette 3301-052), and Paul Jacobs' knowing performance of Debussy's two books of Preludes is enhanced by exceptionally thoughtful documentation (Nonesuch HB-73031).

In the realm of opera and other vocal music, the most enjoyable thing to come my way was the premiere recording of Carl Nielsen's Maskarade, in the splen-did Danish Radio production conducted by John Frandsen (Unicorn UN3-75006). This delicious work, something like a Bartered Bride in the frame of an 18th-century comedy of manners, is the happiest of discoveries, and must leave anyone with ears to hear wondering why it is not in the repertory of all the world's major houses.

After Maskarade, the most striking operatic discovery of the year was The Nose, Shostakovich's youthful tour de force on a story by Gogol, done to a turn by the Moscow Chamber Opera under Gennady Rozhdestvensky (Columbia M2-34582). The fourth installment in Antal Dorati's Haydn opera series, L'Isola disabitata, seems the most downright enjoyable offering so far (Philips 6700.119).

Yvonne Minton and Stuart Burrows are marvelous in Berlioz's Nuits d'ete, with Pierre Boulez and the BBC Symphony Orchestra, and Minton's voluptuous performance in La Mort de Cleopartre on the same disc is a treasure in its own right (Columbia M 34563). Finally, Serge Baudo, who has conducted the Czech Philharmonic in so many fine performances of Honegger's music, has found, in Nelly Borgeaud, an actress who brings utter conviction to the title role in Jeanne d'Arc au bucher, giving us a flesh-and-blood adolescent girl instead of a self-conscious warrior-saint, and the grandly ambitious work comes off in their recording as it never has before on discs (Supraphon 1 12 1651-2).