Why bother?

How early music was performed and whether it matters is good for a rousing argument among music lovers every time it comes up. From piano vs. harpsichord for J. S. Bach to the size of Beethoven's orchestra, there is a nonstop wrangle over the pros and cons of performing old music on old instruments (or copies of old instruments) and in styles fashionable when the music was written.

If Bartok on Baroque instruments and Ravel with seventeenth-century ornamentation (improvised musical decorations) would be laughed out of the concert hall, the anomaly of Mozart on a 1980s grand piano strikes almost no one , because we hear it that way all the time. Music, like drama, requires a middleman to bring it to life. The performer interprets the composer's ideas, and we, the audience, rely on his knowledge.

Ideally, the performer is simply a channel, or better, a focusing lens; so that what looks like chicken scratches on paper becomes an illuminated presentation of the composer's intent in the hands of a skilled and sympathetic player. But it doesn't always work out that way.

Sound, style, instruments, even the number of performers and where they play make a big difference between performers. Add a time warp and the difference is even bigger.

In the literary and visual arts, which don't need a middleman, things have remained pretty well untouched over the centuries. There isn't the urge to rewrite Twain or to repaint Rubens. The same has not held true in the performing arts. Most modern performances of historic works (all works not strictly contemporary) bristle with unintended distortions, anachronisms, misunderstandings and misrepresentations, which magnify with the age of the piece. But, authentic or not, such performances are what our twentieth-century ears are used to, and extremely popular. And maybe a bit boring.

Why is it taken for granted that modern musical instruments are better than the ones they superseded? Contemporary furniture is different from Early American, but is it better? Nobody could call eighteenth- or nineteenth-century Paris fashions inferior in design or workmanship. Ours are merely more appropriate to our day, as theirs were to theirs. So why don't we use old instruments?

For most mainstream musicians, all music is played in the same up-to-date style, Haydn the same as Hindemith. But beginning about eighty years ago with Wanda Landowska and her specially made harpsichord, the feeling has grown and now bloomed into a flourishing movement that music doesn't have to be played all the same way, and that there is a special bonus in trying to approximate the sounds and styles of the composer's day.

Last winter's wildly differing performances of Handel's Messiah around the country are a case in point. Messiah was performed as usual, in late-twentieth-century style, with large chorus, modern instruments and soloists , the whole heavy with opulent sound and wide vibrato. But it was also performed by small groups of singers with Baroque instruments and soloists with ''straight'' (little or no vibrato) voices, the general effect being light and transparent -- very disconcerting to anyone brought up on the former style. And there were dozens of performances in between, of every philosophic shade.

Inevitably, some of those most vociferous against playing eighteenth-and nineteenth-century music -- Bach, Haydn, Beethoven, Schumann -- with original style and instruments are the musicians themselves. It isn't as odd as it sounds. Today's musician is today's man, and he plays today's instruments according to today's values and attitudes toward performance. How he chooses to interpret a work depends on whether he is playing for the glory of the composer, the conductor, or himself. This in turn depends on his sensitivity and intelligence, his education and scholarship (not at all the same thing), and whether he cares a rap about the piece.

In theory, a musician steeps himself in the skin and the times of the composer, from where he can see and hear the composer's ideas falling naturally into place -- sound, size of ensemble, style, technique. And then he performs it , and the performances should be similar whether executed in 1782, 1882, or 1982 .

Nowadays, that's being idealistic, and maybe a bit of a nut.

Many musicians feel threatened by a historical approach to music. They have a lifetime investment in conventional music-making and a vested interest in the status quo. Historical performance practice has not heretofore been emphasized in music schools,!and looks to them suspiciously like a can of worms.

The core of the historical approachis simple. It is that all art belo. - - s own period, and that music can only be performed accurately when clothed in the sound and style in which the composer conceived it. Curt Sachs in his History of Musical Instruments (1940) wrote: ''An outline drawn by Raphael could not be colored with Cezanne's palette. Only the old instruments, the original ones, can express the eighteenth century sound ideals with appropriate colors.'' But does it matter?

Most musicians who try to play early music on old instruments say emphatically ''Yes.'' They point out that even the most familiar music is a revelation when stripped of the accretions of years, like cleaning an old painting and being amazed at the colors underneath. Not only is it exciting, it is also marvelous fun, like treasure hunting. Although learning to play an old instrument is a long, arduous process, the rewards are great, and the accomplished performer can succeed to a remarkable extent in placing us ear to ear, so to speak, with the composer.

Where does this leave the conventional modern musician? He cannot be expected to discard the precious instrument whereby he earns his living, and embrace an antique version of the same. But, thank goodness, old music can be, and is, played on modern instruments, or we would never hear it at all. Luckily it is possible to make a modern instrument sound akin to an old one by changing the way it is played, and at the same time following closely the performing conventions familiar to the composer.

Eventually, perhaps, music students, like art students, will be taught to learn by actually copying the styles and conventions of the old masters, rather than by merely reading about them; and to play on more than one form of their instrument. And then we can look forward to some much more exciting concerts.