A contestant finishes George Walker's "Bauble for Piano," a lyric, midly astringent little test of virtuosity and musicianship that is being played by all the semifinalists this week in the University of Maryland International Piano Festival and Competition. As the applause begins to fill the Tawes Theatre, he steps to the front of the stage, bows to the audience and smiles briefly.

But the smile fades as he looks up, compulsively, involuntarily , to the balcony. That's were the 11 judges are sitting in the semidarkness; nobody else is allowed there during a competition recital. At the end of each performance, they will write on a slip of paper a number between zero adn 25. The highest and lowest numbers will be automatically eliminated and the others tabulated to decide how this contestant stacks up against the other semifinalists. By Saturday night, the 40 contestants whose pictures and musical backgrounds are printed in the program will be whittled down to three. Each of them will play a concerto that night, with ; Sergiu Commissiona conducting the Baltimore Symphony Orchestra. And then the judges will decide who wins the $5,000 first prize, the apperances with orchestras in Lisbon, Rio de Janeiro and seven American cities, the solo recitals here and in Europe, the recording contract. Maryland is one of the major piano competitions of the year -- even in a year when the Van Cliburn Competition has also been held. Sometimes the tebsion is thicker than a Henry Cowell tone cluster played with both forearms.

Everybody knows about the tension among contestants in a big music competition; you can see it in the movies. But what about the tension among the judges? The angry bickering over which judge's pet will win? The soul-searching by a conscientious judge who wonders whether the Horowitz of the next generation will be treated as an also-ran in this competition? Ther are safeguards in Maryland, and most participants have philosophical reservations about competitions, which is also a kind of safeguard. "Don't ask me what I think about competitions -- not in my position this week," said one judge (not for attribution). "I would fell like Hubert humphrey in 1968, when he was running for president and had to defend Lyndon Johnson's Vietnam policies."

There are of course, horror stories about other competitions. "I don't judge competitions anymore," says one prominent musician at the festival who is not a member of the jury. "After an experience out west a few years ago, I decided I would never judge another contest. I sat next to a very famous pianist who slept all through the week -- and then, when the judging came, she was the most vociferous one there. She had come to the competition with her mind already made up."

That doesn't happen at Maryland, partly because the judges do not discuss the compteitors -- each simply enters a numerical score -- and partly because judges refrain from voting at all on performances by a student or a friend. Even extremes of enthusiasm or negativism are neutralized, because the highest and lowest votes for each contestant are discarded. "This is very good lrule," says conductor Pierre Columbo of Switzerland, one of the judges and also the president of the Federation of International Music Competitons. "But not every competition can do it. You ned to have a jury of more than eight or nine; with five or six, if you discard two votes, the others have too much weight. It works very well with 11."

"There's no fighting on this jury, though I've been on some where it was terrible," says Josehp Bloch of the Julliard School, one of this year's judges. "This is a particularly amiable jury -- so compatible that it's almost frightening." Bloch does not worry, either about blighting the life of a potential Horowitz. "We have to trust our own judgement, trust what we hear at that moment," he says.

A competition can be won or lost through a variety of accidental factors unrelated to musical ability, the judges generally seem to agree. "It can be affected by what the contestant had for breakfast, how well he slept the night before, the color of the walls in the concert hall," says Evelyn Swarthout Hayes. "And a judge has to wonder: Am I giving too much weight to the mistakes in the Chopin, not enough to the style in the Mozart? Being part of a jury of 11 gives you a comfortable feeling, because personal tastes and extreme reactions tend to be neutralized."

The judges also feel generally that the loss of one competition is not going to damage any pianist who is really a potential Horowitz. "You do worry," says pianist John Perry, chairman of this year's jury, "That you may have changed the career of someone with talent -- perhaps more talent than the winner. You wonder whether some of the pianists we have admired in the recent past -- Schnabel or Curzon or Rubenstein -- could have won one of these competitions." But he adds that competitions are what interest the public and that he will support them until someone finds another way of identifying young talents and getting them started on a career. "What we really need," he says, "is more contcert activity, a forum for artists to meet the public and become known. We need large, stable, local audiences -- people who will come out and cheer for local musicians the way they do for local athletes. In a sense, the whole musical scene is a competition, and every member of the audience is a judge in his own small way when he decides whether or not he will buy a ticket."