IF YOU WANT to find where the power is in any situation, look for the middleman. In the business end of music, middlemen have long been a thriving species--managers, publicists and booking agencies, to name only a few. Now, a new kind of middleman is emerging, and unlike the (sometimes benign) parasites listed above, his power is artistic, not economic.

Composers, like playwrights and unlike painters or poets, have long had a middleman problem in presenting their art. Unless they were also performers, like Liszt or Mahler, they had to depend on someone else to get the message across. For the half-dozen centuries since composing and performing began to be different specialties, the performer has been in the driver's seat.

Now, it's getting even more complicated. A new middleman, the recording engineer, is jumping into the act with both feet.

On two new Deutsche Grammophon recordings of Mstislav Rostropovich and the National Symphony Orchestra, the name of Wolfgang Mitlehner appears only in the small print on the back of the album sleeve. He is described in that company's polyglot style, as "Tonmeister/Recording engineer/Inge'nieur du son." If the prominence of the credit line were proportional to the power he exercised, Mitlehner's name would be on the front cover in type nearly as large as that used for the name of Rostropovich.

At the recording sessions in the Kennedy Center Concert Hall, Rostropovich was in command of more than 100 musicians, but Mitlehner had control of more than 50 microphones. It is sometimes hard to say which had more influence on what comes out of your loudspeakers when you play the NSO recording of Shostakovich's Fifth Symphony or of Prokofiev's two suites from "Romeo and Juliet."

How many microphones does it take to record a symphony orchestra? Since the arrival of stereo sound, the minimum answer to that question has gone up from one to two--probably three, to fill in the center of the stereo image. Most orchestral musicians seem to feel that this minimum number is also close to the maximum. Excessive mike power encourages audio gimmicks and reduces the conductor's control over the musical results. And orchestral music is still, at least theoretically, the conductor's responsibility.

The presence of Rostropovich can be clearly felt in the energy generated by these performances. The tempos and phrasing are frequently, subtly different from those chosen by other conductors, and there are many accents not written in the score but clearly effective. These are based on Rostropovich's knowledge of the composers, who were both personal friends. Also clearly the work of Rostropovich is the overall interpretation of the music--the deeply tragic impact of the Shostakovich work (which has sometimes been treated as a triumphant celebration) as well as the mercurial shifts from tenderness to violence in Prokofiev's treatment of Shakespeare's great love story. When Rostropovich and the orchestra performed these works last week at the Kennedy Center, these qualities were strikingly present, much as they are on the records.

What is different on the records is the work of Wolf- gang Mitlehner. It becomes noticeable only with very attentive listening and on playback equipment of the highest quality, and it is less apparent in the Shostakovich than in the Prokofiev, whose short, sharply contrasting sections and bright, busily shifting orchestration offer irresistible temptations to the itchy fingers of a recording engineer. The hand of Mitlehner can be detected most clearly with the enhanced clarity of the compact disc format, which is not yet obtainable in the United States but has been marketed in Europe.

The difference between the sound of the live performance and that on the records is something like the difference between going to a play and going to a movie. Mitlehner uses his microphones like a film director working out camera angles, zooming in for close-ups, shifting from one part of the total picture to another. In a sense, he strolls through the orchestra, stopping for a while in the brass or woodwind section and letting the strings fade into the background, or he focuses on a single woodwind that is making a significant statement. With a high-quality stereo system playing a compact disc, the music seems to be all around you, constantly changing in the color and even the relative location of its sounds. It is very different from sitting in a concert hall, say in the center of Row K, and listening to two hours of music from a fixed perspective. And it seriously challenges the conductor's traditional role in deciding what blend and balance of sounds should be heard.

The effect is quite different in the Telarc compact disc of Shostakovich's Fifth with Lorin Maazel conducting the Cleveland Orchestra. In terms of interpretation, I find Rostropovich more exciting and convincing, and the National Symphony manages to play in a class with an orchestra that has a much stronger reputation. But the Telarc sound is essentially that of a concert hall. This company's recording technique is basically to hang up three microphones, set fixed volume levels and then keep the engineer's hands off, allowing the conductor to decide how the music should sound. The effect is more natural, more realistic, though the Mitlehner approach can generate considerable excitement and it does spice up the sound for run-of-the-mill playback equipment.

Which approach is better? Personally, I prefer the Telarc system, and so do most professional musicians I have talked to. But arguments can be made for the kind of sound manipulation heard in the DG recordings. Listening to a record is not the same as sitting in a concert hall, though you can sometimes enjoy a startling illusion if you put on a pair of good headphones and close your eyes. Perhaps it is best to acknowledge frankly that records are a different medium and the music should have a different treatment. Today, a lot of music is being composed with the recording medium specifically in mind, and electronic manipulation of the sound is taken for granted. In general, modern music seems more amenable to such treatment than music of the past. I suspect that Deutsche Grammophon would hesitate to take the kind of liberties with Beethoven or Brahms that it feels free to take with Prokofiev.

In any case, the spirit of truth in packaging might inspire recording companies to put labels on their product, perhaps "Fixed Perspective" when the engineering follows the Telarc philosophy and "Shifting Perspective" when the sound is manipulated as it is on the new DG releases. Or perhaps the labels should read "Natural Sound" and "Unnatural Sound." This would at least allow consumers to shop around for the kind of sound they enjoy.

Perhaps conductors should form a union to negotiate with the sound engineers' union on who has the right to do what in a recording session. And perhaps the name of the recording engineer should be displayed more prominently on some records, so that listeners will know who deserves the credit--or the blame.