Composers who are looking for the very latest sounds in music have not yet come up with anything newer than the electronic systems whose founding father, the RCA Synthesizer at the Columbia-Princeton Electronic Music Center on the Columbia campus, recently celebrated a quarter of a century of activity. There are, to be sure, other systems that appeal variously to composers with different aims in their writing.

It was the RCA Synthesizer that Charles Wuorinen used in writing his remarkably structured "Time's Encomium," which, in 1970, was the first all-electronic composition to win a Pulitzer Prize. Morton Subotnick, who lives and works on the West Coast, prefers the kinds of freedoms offered by the Buchla synthesizer. The differences are practically impossible to explain not only to the layman, but to many non-composing and composing musicians. Wuorinen does give a hint, however, of the strength of the RCA machine when he says that it "is prejudiced by its design toward 12-tone equal temperament. This may be a disadvantage if one is attempting non-tempered pitch relations...."

But are composers today looking for the very latest in sound sources? If they are, they are following in the footsteps of Mozart, who worte his Symphony No. 41 in two versions: one with and one without the new instrument, the clarinet.

And Richard Wagner, who went so far as to invent a new breed of tuba to supplement the brass choir as it was constituted in his day. And Maurice Ravel, who wrote his popular Introduction and Allegro for the newly broadened horizons of the chromatic pedal harp. And, to move back in time again for a moment, Ludwig van Beethoven, whose piano sonatas give a clear picture of the steady improvements in range and dynamics of the piano as he lived with it.

Yes, many composers are today interested in the newest possibilities in sound sources, but they are by no means confining their investigations to the electronic regions. Instruments like the pipe organ, that reach back to the medieval ages, are being put to uses Bach would not have employed, but which are completely valid in the light of historical practice. For his "Improvisation Ajoutee," written in 1962, Maurice Kagel calls for a four-manual organ (the standard larger instrument these days,) and "two or three other performers in addition to the organist himself." (Even that is not a wholly new concept: Franz Liszt, in his "Ossa Arida" requires either an organist with three hands, or two performers at the keyboard.)

Kagel asks these extra "performing registrants to carry out changes in registration during the course of the performance, thus facilitating rapid changes in timbre that would not otherwise be possible." They also are called upon, from time to time, to add to the sound of the organ "in a tone-color scale ranging from humming to shouting." Shades of Sigfrid Karg-Elert! His tour of this country nearly 50 years ago was memorable, in part, at least, because his daughter stood on his right as he was playing and performed such useful duties as holding down long notes for which the performer lacked the necessary extra finger (he did say in the score that organists without daughters were free to insert pencils or similar objects under the keys for the proper duration of the notes), as well as changing the stops and operating the expression pedals as called for. (She did all these things and at the same time chewed gum, often pulling it out of her mouth and then letting it back in again.) It almost makes Kagel look like something of a piker.

Kagel is, however, by no means a piker. He is one of the most inventive of the more avant-garde composers today in letting his imagination conceive of new sounds from old sources.

For example, in "Der Schall," which is the German word in physics for "sound," Kagel calls for only five players. But they are in charge of 54 insturments! These include items one might not have expected, such as foghorn, spaghtetti tube with trumpet mouthpiece, 20 meters of garden hose with plastic funnel, antelope horn, conch trumpet and an exotic gadget called a rubberphone (which is, to satisfy your curiosity, a group of rubber bands that are plucked.) Enough? But wait! Kagel also wants, in this same work, 12 organ pipes to be blown by mouth (that's the bit I thought Bach would not have tried), two brass tubes, a "genuine Cagniard de la Tour siren" (which is a blown siren), with a frequency measuring device, a cuckoo (which is not what you think, but a sort of seesaw with two bellows - now do you understand? - four tortoise shells and a telephone.

He wants a good deal more but that gives you the idea. Not all of those requirements are new, either. Gian Carlo Menotti was not the first to use the telephone in an opera, nor Poulenc the last. And George Antheil called for a typewriter half a century ago in his "Ballet Mecanique."

Perhaps composer Gottfried Michael Koenig puts the whole current scene into a clear light when he says, "An electronic studio does not supply the composer with sound-material from which he merely has to make a selection. The studio rather resembles a construction kit, the components of which have no musical significance of their own. This involves the composer in working methods that greatly differ from his habitual ones. He may try to imagine sounds he never heard before, and to produce them in the experimental phase of his work."

Today every major musical city, and most minor ones, have an electronic music system. In this country every university with a music department of any size has its own. It's like hospitals with their CAT scanners.

In terms of wise popular appeal, however, no composition by any composer has yet established itself as an item of the standard repertoire. But record catalogues tell a different story from our concert halls. Schwann catalogues have for a long time carried a separate section for electronic compositions, whose basic characteristics are ideal for multi-channel reproduction.

Performers who have grown up with all the newest sounds in music have adapted their own techniques to match the new creative ideas. Phyllis Bryn-Julson, one of the most gifted singers before the public today, sounds as much at home with George Crumb's most exotic ensembles or John Melby's electronic tape accompaniments to poems by Wallace Stevens as she does singing Sir Edward Elgar in the Kennedy Center or in Roger Sessions' "Montezuma" with the Opera Company of Boston.

Compositions cast entirely in electronic sound now are being written for almost as many purposes as mucis from any other sources. There are works called "Music for a Sacred Service," and "Mass," and others entitled "Lemon Drops" and "Sidewinder." John Eaton's "Mass," commissioned by the Koussevitzky Foundation in the Library of Congress, had its world premiere there in 1970 and was repeated two days later in the Washington Cathedral. Incidentally, Eaton, on the faculty of the University of Indiana, likes to work with Moog synthesizers in combination with several Synkets, which are smaller, more flexible keyboard-operated synthesizers.

With inescapable logic, notation has kept up with the newest ideas in composition. In recent years it has become commonplace for performers to have to read, digest, and understand new signs and symbols, entirely new signals and road guides to the new music they intend to perform. This has been, at times, a headache not only for the performers, but for the publishers whose fonts of clefs, staves, leger, and notes in values from whole notes up, or down, to 128th notes were no longer up to the job of indicating a composer's intentions.

How to handle new kinds of notation without putting the entire music publishing business into bankruptcy? Photoduplication was the answer. The composer sends the publisher his final clear, but at first incomprehensible score. The publisher does not have to have an engraver decipher it or seek some way of getting it onto his standard manuscript page. The original score is duplicated and made available to performers precisely as it left the composer's desk.

A final word: From week to week there is more and stronger evidence that younger composers are looking toward more immediate communication with audiences. Krzysztof Penderecki, in speaking of his new opera, "Paradise Lost," said flatly, "My music is today probably 90 percent changed from what it was 10 years ago."

And Joseph Schwantner, who recently won this year's Pulitzer Prize, has said that he wants to write music that will have an appeal for audiences at first hearing. Electronic music may fit into this new cycle more effectively than it has, thus far, managed to establish itself during the past quarter of a century. As for the new sounds from old sources, they are simply continuing one of the oldest traditions in the making of music. CAPTION: Illustration, no caption, by Juanita Mondello for The Washington Post