The system under which the Philadelphia Orchestra became one of the very greatest, if not the greatest, virtuoso orchestras of all time is about to be changed.

Next year, when Eugene Ormandy leaves his post as music director to be come laureate conductor, it will be the end of a 68-year period in which the orchestra's musical destiny has been under the direction of just two men. Leopold Stokowski headed the orchestra he made great from 1912 until his resignation in 1936. Ormandy's reign has been unbroken since.

There are strong differences of opinion among members of the committee searching for Ormandy's successor about who he should be. The heart of the argument is clear: The Philadelphia Orchestra was created by Stokowski and Ormandy, who made it their full-time work. Should their system now be discarded in favor of a new one that has not worked as well anywhere?

When Stokowski took on his Philadelphia post after three years as conductor of the Cincinnati Symphony, he moved to Philadelphia and made it his permanent home, spending his full time and energy establishing the orchestra's greatness. When Ormandy took over from Stokowski in 1936 after five years in Minneapolis, he, too, made Philadelphia his permanent home and spent all his time and thought molding it. (Frederick Stock did the very same thing in Chicago from 1905 to 1942, and Serge Koussevitzky in Boston from 1924 to 1949, and the results were of the same unusual order.)

During their years in charge, Stokowski and Ormandy did little, if any, guest conducting. Their seasons were filled with the concerts of their orchestra at home and on tour, and with the increasingly heavy recording schedules requested of both men.

Now that system is about to be changed if the frequently reported rumor that Riccardo Muti, the Philadelphia Orchestra's principal guest conductor, is to be named Ormandy's successor comes true.Muti, who is 37 and was born in Naples, will not make his permanent residence in Philadelphia should he get the prize assignment. He is in charge of the "Maggio Musicale," the opera in Florence, as well as principal conductor of the New Philharmonia Orchestra of London. These are posts he would retain along with the Philadelphia job.

It is precisely on that point that some members of the search committee are strongly opposed to the Muti appointment. And they are right. They want someone who will come to their great orchestra and see its conductorship as the supreme opportunity of a lifetime, a position in which to remain for the balance of a career. A move to Philadelphia would, to such a musician, be the logical step, a part of the total picture in which the man at the head of the Philadelphia Orchestra rightly becomes one of the most honored citizens of that city.

The question arises, why not ask an American conductor? Recently, I was challenged by a member of the staff of the Philadelphia Orchestra to "name an American conductor for this spot."

It is a pleasure to be able to name 25 American conductors, ranging in ages from the late 20s to the early 60s, each of whom has a combination of experience and repetoire parallel to, or greater than, that which Ormandy brought to the post in 1937. The orchestra was already one of the world's great ones. Ormandy was selected, as the official orchestra biographer wrote, "over many other musicians more experienced and renowed." His reputation for solid music-making had been built in his Minneapolis years, but he has not widely known.

Some of the following American conductors may be very familiar names, but each has distinguished himself in the field and most have been conducting major orchestras over the years.

Some have won the world's highest awards for conducting and have served as associates of some of the world's leading conductors. A number of them having outstanding recordings to their credit. They are listed not as recommendations for the Philadelphia post, but because they offer qualifications that seem preferable to Muti's:

In alphabetical order: Guido Ajmone-Marsan, Michael Charry, James Conlon, Dennis Russell Davies, James DePreist, James Dixon, Lawrence Foster, David Gilbert, Christopher Keene, Robert LaMarachina, Louis Lane, James Levine, Henry Lewis, Lorin Maazel, John Mauceri, Jorge Mester, Thomas Michalak, John Nelson, Michael Palmer, Maurice Peress, Andre Previn, Kenneth Schermerhorn, Robert Shaw, Leonard Slatkin, Michael Tilson Thomas.

Some of these conductors undoubtedly would not be right for the Philadelphia Orchestra. Some might refuse the post if it were offered. But they are among the top conductors in this country and their time could be given exclusively to Philadelphia, which is essential if that orchestra is to escape the homogenized kind of sound and repertoire that comes from so many of our top orchestras these days whose conductors spread a limited repertoire and limited time over several enterprises.

Two observations were made by a representative of the Philadelphia Orchestra in supporting the Muti candidacy-that "the ladies are so crazy about him" and "he comes with a recording contract."

If it is a fact of life that a conductor's looks are a part of the charisma that lands him a job, then, somewhat unwillingly, I would suggest that young Ajmone-Marsan would hold his own in any conductorial competition for sheer handsome appearance. But let's be serious. As to the recording contract bit, the Philadelphia Orchestra at present enjoys the unusual situation of being heard at its best on Victor, Columbia and Angel records. No one is going to take seriously the suggestion that the music director of the Philadelphia Orchestra has to provide his own recording contract.

What is more essential in a time when the conductors of our biggest name orchestras are seldom Americans is that the man who takes over the Philadelphia should have some sense of this country's musical greatness. That is something that does not come from Naples.

Only weeks ago Cincinnati hit bottom by announcing that its late, great American conductor, Thomas Schippers, would be followed by Michael Gielen, a German who has never even conducted the Cincinnati Symphony! What a great thing it would be if Philadelphia were to decide that the first requirement for its new conductor is that he should be an American. Have you some strong reason why not?" CAPTION: Picture 1, Ormandy directing the Philadelphia Orchestria in 1939.; Picture 2, Riccardo Muti is a candidate for Ormandy's job, but he'd continue his work with other orchestras. AP