Dimitris Sgouros reached speeds last night, in parts of Beethoven's "Appassionata" and Liszt's "Mephisto Waltz," that might get him into the "Guinness Book of World Records." But that is not the news about the 12-year-old Greek pianist, and it is presumably not what earned him two standing ovations and two encores in the opening program of the University of Maryland Piano Festival.

What Sgouros proved last night, in his first solo recital in the Washington area, was that he is not merely an athlete (which he certainly is) but a musician as well, and potentially a musician of memorable stature. His remarkable hand-and-eye coordination has been clear since April, when he made his American debut with Rachmaninoff's Third Piano Concerto in Carnegie Hall. And last night's audience, made up largely of fellow pianists attending the festival, was not the kind to be stampeded into ovations by mere demonstrations of speed, strength and accuracy. Sgouros gave them considerably more than that; besides coming on as 1982's most exciting version of The Great Juvenile Piano-Playing Machine, he showed a kind of precocious maturity that may eventually be seasoned into greatness.

Technical prodigies are not particularly rare today, perhaps because of the increased vitamin content in our food. But musical perception at the highest levels is always unusual and always especially welcome. Sgouros is not yet at those rarefied levels, but he shows a very clear promise of the ability to reach them with the proper teaching and experience.

There must be a strong temptation, when nature hands you the equipment to zap audiences with pure technique, to let it go at that. But Sgouros showed higher aspirations in the slow movement of the "Appassionata" and the more tender interludes of the "Mephisto Waltz"--above all, perhaps, in the overall shaping of Chopin's great Fantasy in F minor, which can easily become a disjointed anthology of Chopin styles and special effects if the music is not subjected to a clearsighted, unifying intelligence.

In Schumann's Symphonic Etudes, except for an occasional small imbalance between his left and right hands he was a complete success. This does not mean that he made the work sound musically interesting; he played it as a very thorough and highly varied series of purely technical exercises. But that's what this music is all about; those who bring poetry to it are adding something from the outside, and this Sgouros either refused or was unable to do. But where the poetry existed--in Beethoven, Chopin and parts of the Liszt, he was aware of its existence, its qualities, and the kind of phrasing and dynamics required to make it stand out.

Still, in terms of poetry, he is not a remarkable musician, merely a remarkable 12-year-old; where he really shone last night, as in previous appearances, was in technique. He is sometimes very near the level of pure dexterity that made Vladimir Horowitz the wonder of the musical world a generation ago. This showed not only in the remarkable speed of the Presto finale in the "Appassionata," but earlier, in the long, glittering cascades right after the dramatic introductory statement, where each note was clearly articulated and distinct at breathtaking speed. Many pianists blur this music slightly, perhaps to cover occasional wrong or dropped notes. Sgouros was not mechanically perfect in every note, but this did not matter. Pianists seldom are, and Sgouros' mistakes were meaningless because he was playing the music, not a mere technical exercise.

His ability to differentiate and balance voices was musically very impressive, as was his knowledge of how to accent both lyric and dramatic passages, not only through dynamics but through phrasing. His mastery of agogic accents--the little rushes and hesitations that give the music a pulse of life--was impressive in Beethoven and dazzling in Chopin, where such niceties are essential to the music's meaning. The Beethoven, except for technical fireworks, was a fairly standard performance without much individual personality, but he has already put the stamp of his own personality on the way he plays the Chopin.

These performances will certainly grow as the pianist grows, and in 10 years, if all goes well, Dimitris Sgouros could become not merely an ex-prodigy but one of the most remarkable musicians of his generation. Between now and then, he has a lot of growing to do, and most of that growing should be done without audiences.