"THE PIANO is everywhere and always wrong in Bach." Got that?

This is a rather vigorous statement of a standard critical opinion of the late 20th century. It was written in 1970 about a Bach concert played by pianist Rosalyn Tureck, but it could have been written about many other pianists, including the late Glenn Gould or Brazilian Joao Carlos Martins, who will be doing a special sort of piano-Bach program in a few weeks at the University of Maryland's International Piano Festival.

In its extreme form, the phobia against Bach on the piano may be called "the Landowska fallacy," in honor of Wanda Landowska, the gallant lady who rescued the harpsichord from oblivion two generations ago. It is not a fallacy to prefer the harpsichord for Bach, but it is usually a fallacy to use words like "everywhere and always."

The question about what instrument to use for Bach is more than one question--not only "What did Bach want and expect?" but also "What works musically?" and even (whisper it!) "What do audiences like?"

There is more than one way to spin out a toccata or a sarabande. Bach has been performed with artistic and box office success on instruments he never wrote for, likethe guitar or brass quintet, and on instruments he never dreamed of, such as the harmonica and the Moog Synthesizer, not to mention the scat-singing voices of the Swingle Singers.

Tureck, who is now 68, began to play Bach on the piano in the 1930s, and developed a special style for that purpose. If this was a crime, she is the godmother of a flourishing syndicate. Gould, for example, first heard her on records when he was in his teens and was developing his own Bach style. She convinced him that he was not as crazy as people said he was.

"My exposure to her records was not perhaps so much a question of influence as of reinforcement," he later recalled. "It was nice to know that somebody else was working in essentially the same direction."

Then there's the Johann Sebastian Bach International Competition, which will be accepting applications until July 1 and will be held Sept. 23 through 25 in the Lisner Auditorium.

For this competition, which is observing its 25th anniversary, some of the world's leading musicians regularly serve as judges.

It is one of the most scrupulously fair competitions in the world. Screens separate the judges from the contestants so that it is impossible for the judges to know who is playing, and the security precautions even include a carpet between the wings and the piano, so that the judges cannot hear footsteps and guess whether the contestant is a man or a woman.

Raissa Tselentis, founder and director of the competition, remembers one year when the first prize went to a woman and a German-speaking judge was shocked when he saw whom he had voted for.

"Mein Gott!" he shouted. "Ein Weib!"

Contestants must play from memory one or more of Bach's major works. Usually, they have no choice of repertoire. For this year's competition, which is dedicated to the memory of Glenn Gould, they are allowed to choose between Book I and Book II of the "Well-Tempered Clavier," which is like choosing to scale either the east or the west slope of Mount Olympus. It will be the first time that this music has ever been featured as the sole test of accomplishment in any international competition.

Martins, who made his American debut in Washington in 1961, playing all 48 preludes and fugues of "The Well-Tempered Clavier," is now embarked on "The Bach Tri-Centennial Recording Project" for Arabesque Records.

By 1985, when Bach's 300th anniversary is celebrated, he plans to have all the keyboard works recorded (in superbly clean digital sound) on the piano. Parts of the project released so far include the "Well-Tempered Clavier," the six Partitas, the "Goldberg" Variations and the "Italian" Concerto, and they make me want to hear more.

Occasionally, he romanticizes a bit, with subtle dynamic shadings unavailable on the harpsichord or little shifts in the tempo--but the music sings, and it often sings simultaneously in several beautifully limned voices. He sometimes reminds the listener of Bach's influence on Chopin, and he will do that even more emphatically on July 18 when he performs a duet concert at the University of Maryland with fellow Brazilian pianist Arthur Lima.

Martins will be performing Bach preludes and Lima will be performing those of Chopin in the same key signature. One conclusion certain to come out of the experience is that our musical life is richer because Chopin played Bach on his piano.

As for others, the general rule is that a piano performance may or may not be good for Bach's music, but Bach's music is certainly good for pianists.