Cyprien Katsaris, who'll be performing with the National Symphony Orchestra at Wolf Trap this Friday night, has begun to record a complete cycle of Beethoven's symphonies. There's nothing terribly odd about this except that, as Katsaris points out, "I'm not a conductor, I'm a pianist."

As his records eloquently attest, he's a pianist especially at home with romanticism. He has a talent for making the keyboard sing, a rich tone that he varies exquisitely, and a sense of phrasing (rushes, hesitations, subtle shifts of emphasis) that gives his hands many of the qualities of a speaking or singing voice. You need all of these, of course, if you're going to play Beethoven symphonies on a piano.

The first record in this series (Telefunken 6.42781 AZ) is the "Pastoral" Symphony, Beethoven's Sixth and in many ways most colorful symphony, with its evocations of a walk by a brook, birds singing, a country band playing peasant dances, a storm and a final hymn of thanksgiving as the storm fades away. Katsaris is aided by Franz Liszt, who transcribed the symphonies for piano with amazing precision and detail, though Katsaris has gone back to the orchestral score and added a few touches -- a flute line here, a bassoon or tympani there -- that Liszt left out. His next recording will be the Ninth Symphony, already taped.

Although he's planning to eventually record all nine symphonies in Liszt's transcriptions, Katsaris insists that "I do not intend to be just a transcription player. This is not what I do."

Clearly, Katsaris wants to stay in the mainstream, where most of the action is, while pursuing his interest in some of the less-familiar byways of the piano.

With the NSO, he'll be playing Tchaikovsky's First Piano Concerto -- about as mainstream as you can get. But on records, he has turned his attention to some fascinating and largely neglected repertoire, which he performs with a high level of intelligence and technique: the 23 mazurkas of Scriabin, plus waltzes, polonaises, impromptus and other short, enigmatic pieces, on Pathe- Marconi C 181-16298/9 (two records); some fine and seldom-heard sets of variations, including Schumann's magnificent "Exercices" on a theme from Beethoven's Seventh Symphony (Telefunken 6.42787 AZ); a collection of unusual encore pieces, also issued by Telefunken (6.42479 AP), which focuses on composers' borrowed ideas, as in fellow pianist Gyorgy Cziffra's hair-raising "Flight of the Bumblebee."

But it's Liszt who inspires Katsaris' taste for the offbeat. One of his recordings of Liszt's works for piano and orchestra (Angel DS 37888), made with Eugene Ormandy and the Philadelphia Orchestra, includes the "lost" Concerto in the Hungarian Style. Long attributed to Liszt's pupil Sophie Menter, the concerto was actually, we are told, written by Liszt and orchestrated by Tchaikovsky. An album of Liszt solo piano works includes the rarely heard "Mephisto" polka and the atonal "Bagatelle sans Tonalit,e," as well as the four "Mephisto" waltzes, of which the first ranks among Liszt's most popular works.

Even in a collection as frequently recorded as Chopin's waltzes, he includes posthumously published works often omitted from "complete" records. But for most of this collection he's playing material recorded by dozens of other pianists. Katsaris stands up very well in the comparison, with fluent, extremely well-recorded performances that are delightful, among other virtues, for his superb calculation of when and how long to pause and let the music hang breathless.