Allan Kozinn writes frequently about music and musicians.

''Orpheus is the particular blend of freedom and responsibility that goes with working as a chamber orchestra without a conductor,'' the cellist Julian Fifer says of the unusual ensemble he founded in 1972, and which is giving the first of three 10th-anniversary concerts tomorrow evening at Carnegie Hall. ''Part of the responsibility,'' he explains, ''is that we must all know the music, including each other's parts, much better than we would have to if there were a conductor on the podium. But the freedom is that we can all contribute to the interpretation, during rehearsals, and that we can interact more spontaneously in performance. The idea, from the start, has been to approach the orchestral repertory we play as chamber music - and, in fact, to also include chamber works on our programs, so that we can work together in smaller groups and get to know each other's playing better than we would in an orchestral situation.''

During its first decade, Orpheus has grown from a 15-player ensemble that gave a few chamber concerts in churches and libraries around town, to a 26-piece chamber orchestra that has toured the United States, South America, Europe and parts of the Near and Middle East, and which has also made a half-dozen recordings.

Orpheus is, basically, an orchestra of freelancers - that is, its roster is fixed, and boasts a low turnover rate. But since Orpheus plays only about 65 concerts a year, its players also hold teaching posts or perform as soloists, in other chamber groups, or even in symphony orchestras. Within the ensemble, there are no principal players; rather, the members of each section rotate, and the whole ensemble elects a new concertmaster for each work it plays.

Yet, despite these mercurial qualities, Orpheus has earned a reputation for performances that are not only enthusiastic and fresh, but which are often as well shaped and finely polished as many a more firmly established, conducted orchestra. On the surface, it would seem that fashioning orchestral performances without the guiding hand of a conductor should present both technical and interpretive problems, particularly in the post-Classic literature. But the success Orpheus has enjoyed raises several questions: Is a conductor really necessary? Or, conversely, can a musical interpretation be established by committee? And how can orchestral discipline be maintained among 26 soloists with, theoretically, an equal say in the ensemble?