Of all the Romantic composers, it was Robert Schumann who - particularly in his piano music - immersed himself most totally in the new wave's freedom from calssical forms and in its license to be daring. Like a musical Byron, Schumann set out to explore to its limits the range of compressed mood and color made possible by the new esthetic.

At the same time, Schuman had the additional advantage of being one of the first composers to work with pianos built with the sonorities of the modern concert grand. The combined result was an expanded language of piano composition - with a rhapsodic abandon and free form that lay somewhere between Chopin's carefully structured concentration on mood and pure sound that was to come with Debussy.

Claudio Arrau and Vladimir Horowitz are probably the most eloquent exponents of Schumann's musical language now before the public (a qualification that eliminates Arthur Rubinstein and, at least recently, Sviatoslav Richter). Both have a special sensitivity to mood and sonority that is fundamental to Schumann piano-playing.

Of the two pianists, though, Arrau is by far the more prolific recording artist. For some time he has produced Schumann records at a rate of about one per year. Now comes a disc (Philips 6500 395) with four Schumann works, each quite different in character, that when thrown next to each other strikingly illustrate the range of the composer's poetic vision. They are "Papillons," "Kinderszenen," the three "Romances" and "Blumenstuck." With these remarkably sensitive performances, Arrau has put himself well on the way to doing Schumann's complete piano works.

"Papillons" ("Butterflies") is an early example of the sets of short, highly contrasted vignettes with specific literary references that were quite consciously small poems in sound. In musical terms, these works are to movements of sonate and symphonies what short stories are to novels.

One of the works for which "Papillons" is a precursor is "Kinderszenen," a sequence of 13 short pieces, each of which evokes a childhood experience as recalled by the adult mind. "Kinderszenen" is one of those subtle works that are simple to play and devilishly taxing to interpret. This performance is a particular test for Arrau, because the work is a Horowitz specialty (Columbia-MS 6411). Comparing the two, the outcome is six of one, half a dozen of the other. The Arrau interpretation is gentler and his tonal color is warmer.

But Horowitz is the more precisely disciplined and in that most famous of all Schumann's piano vignettes, "Traumerei" ("Reverie"), Horowitz maintains a chaste, even line that superbly captures the purity and, thus, th innocence of the work. By bending the line farther, and becoming more sentimental, Arrau is more like an adult trying unsuccessfully to sound innocent. In the last section, "The Poet Speaks," Arrau avoids this pitfall, in a beautifully understated performance that is a touch more mellow than Horowitz. My advice is to own both recordings if you can.

The three Romances present a more complex, worldly side of Schumann, on the level of, say, "Kreisleriana." The textures are thick and sonorous, with all sorts of inner voices that Arrau brings out to enrich the effect. These are very much works about adult experience. The first Romance, in B-minor, is a study in lowkey emotional uneasiness - that point at which one first begins to feel apprehension, expressed though ambivalent balancing of major and minor keys and unexpected harmonic turns.

The second Romance is a more reflective, understated work that prepares the listener for the boldness and panache of number three. It is a musical portrait of euphoric selfconfidence, with a strutting main theme, full of syncopations and surprise extra notes that complicate, and sophisticate, the experience. Arrau handles this Romance with a swagger that utterly eclipses previous recordings. In fact, the record would be highly recommended for the Romances alone.

The final work, "Blumenstuck," is lesser by comparison with the three preceding works, but it is good to have. It lacks that specificity of mood that Schumann habitually sought, and that is present in virtually every other measure of the pieces on this very fine record.