The piano recital is one of the few institutions of mankind that has not only survived the cultural shocks of a century, but actually seems to be flourishing on a grander scale than ever. Maybe that's because in an age which struggles to preserve a few last shreds of private identity, the solo pianist - like an Olympic contestant or an astronaut - is one of the few who takes the stage all alone and comes to grips with a supreme challenge. Vicariously, we all become heroes as witneses.

At the University of Maryland all this week, piano freaks have been enjoying an unusual marathon of performances, classes, demonstrations and trials, all devoted to the art of ivory tickling.

What's unusual is the mix. There are lots of competitions, but few are held in the presence of so many notable performers, and are as free of cutthroat tensions as the Maryland event. There are lots of festivals, but struction and study that characterizes few set in the context of mutual in Maryland's International Piano Festival and Competition.

This was particularly evident Wednesday morning when Paul Jacobs conducted a master class in 20th century music, coaching three Maryland University students in performances of the Copland Piano Variations, Schoenberg's Piano Pieces, Op. 11, and Stravinsky's Piano Rag Music and Four Etudes. Op. 7. He also gave a brief introduction to the music of his own recital program, and in particular, to the immensely difficult and intellectually challenging Klavier-stuecke Nos. V and MI by Karlheinz-Stockhausen.

Jacobs a pianist of prodigious abilities who has made avant-garde music his domain of specialization, has the innately droll manner of Tony Randall when he's speaking. "Alas, my program tonight is going to be all 21-tone music," he began. "Fasten your seat belts, it's going to be a rocky night."

Then he launched into an historical survey to explain how Stockhausen's music "got the way." By the mid-'50s, Schoenberg's precocious pupil Anton Webern had became the patron saint of the avant-garde. Even Schoenberg himself was considered old-fashioned. Jacobs recounted a lecture by French critic Andre Hodeir declaring that Schoenberg was the "Moses who showed us the way to the Promised Land, but was not permitted to enter it himself."

Striding to the Keyboard, Jacobs produced a large brown paper tube from which he drew an enorous scroll of music and a dolded wooden music stand. "Ten days before I was to premiere the Klavierstueke No. XI this arrived in the mail," he explained. It was the Stockhausen score, typically eccentric in format. "You can see why we began to call it Rack and Roll piece." Later on, after elucidating the intricades of the work's construction and demonstrating passages at the piano, he raised the huge manuscript aloft again and remarked, "Even if you don't like the way it sounds, you can always use it as a lampshade."

There was, however, as much illumination as amusement in his commentary. To the student performing the Copland Variations he noted: "When I played this for Copland1 he stopped me at his passage and said, "this part has to be played like Brahms.' You'd never know it, he didn't put it in the score, but he wants you to be as romantic as you know how - each phrase with a big breath, with a dream."

To another, going through the Stravinsky Piano Rag: "You've got to hear this figuration like a trombone glissando . . . . Waaa, Waaa, Waaa," and instantly the performance took on the flavor it had seen missing.

To the Schoenberg interpreter: "That's really fine - the only things, I think the playing needs to brood more, with a darker, more somber sound. Eduard Steuermann used to describe this piece as 'a lunar landscape' - bdeak and desolate."

Rosalyn Tureck's all-Bach recital last night at the University's Tawes Theater was the final installment in a week of recitals that also included appearances by some of the biggest guns of piano: Malcolm Frager, Philippe Entermont, Rudolf Firkusny, Paul Jacobs and Hans Richter-Haaser. During the same interval, close to 200 full-time enrollees, and scores of other students, teachers and professionals, have attended master classes and lecture-recitals by the resident artists and other pianists. At the same time, 15 young contestants from throughout the country and six foreign nations have been ascending through the stages of a competition that reaches its climax tonight, in a round of finals to be accompanied by conductor Sergia Comissiona and the Valtimore Symphony.

The festival is the University of Maryland International Piano Festival and Competition, taking place for the 7th year in a row under the direction of Maryland's piano faculty chairman, Steward Gordon.

The festival has actually been in existence, in a somewhat different form in the early years, since 1965, when the Matthay Festivals started as a summertime happening on the Maryland campus, and out of which the international conclave grew. By now, it has evolved into a phenomenon unique in the piano world. In past years, it has attracted artists Alicia De Larrocha, Byron Janis, Jorge Bolet, Lili Kraus, the late Gina Bachauer, Alfred Brendel, John Ogdon, and Charles Rosen to the Tawes stage. The repertoire has included jazz and the furthest edge of the avant-garde, as well as the classical mainstream.

The atmosphere that reigns in the Tawes hallways, a camaraderie born of shared dreams, problems, anecdotes and anxieties, is unusual too. So is the audience drawn to the nightly concerts - conspicously diverse in age, sex and background, but all highly sophisticated when it comes to piano playing. One senses this in subtle ways. At a point in a recital where one would normally expect thunderous applause to crash in on a final note - as after Frager's encorge performance of a delicate little Chopin Contredanse - instead there were a few moments of breathless silence to allow the quiet mood an undisturbed repose, and then, and then only, the deluge.

In this atmosphere, the distinctions between stage and classroom tend to fade. The recital becomes an occasion for learning, and to an extent also, the classroom, becomes a theater.