There is only one reason for buying recorded music on open-reel tape as opposed to discs, cassettes or even (heaven forbid) eight-track cartridges. The reason is that this medium is the best, both for fidelity of sound and for long-term use without loss of quality. Either this means more to you than the relative inconvenience of tape (threading it on a pickup reel and sometimes fast-winding it to reach the music you want) or it doesn't. If it does, read on.

In the last few years, there has been a good reason why people weren't buying much music on open-reel tape. They couldn't. Always a small, connoisseur's market, the open-reel format withered away to nothing at all when cassettes began to be a mass medium and a vehicle of true high-fidelity sound. The best cassettes (those produced by Advent, for example) are, in fact, excellent, but there is always a theoretical superiority (and usually and audible one) in open-reel tape, based on the simple fact that the tape is wider, travels four times as fast, and therefore has much more capacity for storing sound.

Unavailability is no longer a valid reason for not getting at least some of your music on open-reel tape - though acquiring the tapes, like using them, requires a little more effort. An enterprising mail-order firm, Barclay-Crocker (11 Broadway, New York, NY 10004), specializes in these tapes and has begun producing its own from masters provided by a variety of record companies. It has been doing this for less than a year, but already its catalogue is beginning to show an abundance and variety to warm a connoisseur's heart. The performances (by internationally famous musicians and unknowns alike ) are generally good and the company's technical quality-control standards are quite simply the finest I have encountered from any producer of commercial recordings.

In a later column, I hope to discuss at greater length one part of the Barclay-Crocker output: the tapes derived from the very imaginative English company, Unicorn, whose products are only spottily available in this country. For the moment, space will permit only a brief sampling of material from Barclay-Crocker that is already available (and in many cases well-known) on discs and/or cassettes. I have played each of the items listed below repeatedly and with great enjoyment - of the music and performance, to be sure, but most particularly of the rich, natural, transparent sound.

Kodaly: Duo, Opus 7 for violin and cello, Sonata, Opus 8 for cello unaccompanied. Paul Olefsky, cello; Leonard Posner, violin (Musical Heritage MHS C 3047). In these two works, particularly in Opus 8, Kodaly was for once the equal of his friend Bela Bartok; the music is deeply rooted in Hungarian folk idioms, primitive-modern in flavor and dazzling in terms of pure technical display. The performances and sound are beyond criticism.

The Demonic Liszt. Earl Wild, piano (Vanguard D 10041). When diabolical themes crept into his music, as they did fairly often, Liszt sometimes composed like - well, yes, like a man possessed. The phenomenon is well known from the first of his "Mephisto Waltzes" but equally perceptible in the less-known and very strange "Mephisto Polka" and the eerie "Dance of the Gnomes." The effect is less monomaniacally sinister in his pianistic tributes to three of his favorite operas, "Robert le Diable," "Don Giovanni" and Gounod's "Faust," but they are spectacular examples of colorful piano writing. Earl Wild does the music complete justice - no small feat.

The Harpsichord Now and Then: Selections by Bach, Rossi, Howells, Busoni, Martinu, Shackleford. Lary Palmer, harpsichord (MHS C 3222). An imaginative and splendidly performed collection, illustrating the harpsichord in its early years (Rossi), its 18th-century heyday and its modern rebirth. Side two, containing the modern compositions, is especially impressive, even without resorting to the better-known harpsichord works of such composers as Falls, Poulenc, Thomson and Cage. The instrument's special tang is captured on this tape with exceptional fidelity.

Rachmaninoff: Symphony No. 3 in A minor, Op.44. Vocalise, Op. 34, No. 14, National Philharmonic Orchestra, Leopold Stokowski, conductor (Desmar D 1007). One of the last recordings made by the great conductor and one of the best, this tape comes as close as an electronic system in the home can to reproducing the sound of an orchestra in a concert hall.

Mahler: Symphony No. 4 in G. Netania Davrath, soprano; Utah Symphony Orchestra, Maurice Abravanel, conductor (Vanguard D 10042). A good, meticulous performance (though others are marginally better) in sound that would be hard to surpass.

Gottschalk: Music for piano four hands and two pianos. Eugene List, pianist, with Cary Lewis and Joseph Werner, second pianists (Vanguard D 71218). Gottschalk is the earliest American composer who has a substantial audience today, for reasons that this bright, light music quickly makes obvious. Among the dozen relatively unknown (and eminently knowable) works in this collection are "The Union," a clever tapestry of patriotic airs such as "Yankee Doodle" and "The Star-Spangled Banner"; "Souvenirs d'Andalousia," which remarkably anticipates Lecuona's "Malaguena"; various bits of colorful description, romantic sentiment and plain, enjoyable melody. List validates fully, once again, his right to be considered the prime interpreter of Gottschalk in our time.

Leroy Anderson: Fiddle Faddle and other Favorites. Utah Symphony Orchestra, Maurice Abravanel, conductor (Vanguard D 10016). Morton Gould: Latin American Symphonette. Gottschalk: A Night in the Tropics. Grand Tarantelle for piano and orchestra. Performers as above, with Reid Nibley, piano (Vanguard D 0275). Light, enjoyable music in excellent performance and sound.