The Music Notation Modernization Association held its second international conference at St. Louis' Fontbonne College late last month. Those in attendance ranged from academics to amateurs, from composers to inventors, from reticent observers of the situation to aggressive revolutionaries. They all had ideas, and most of them seemed convinced that their ideas were the ones that would someday make a difference. Perhaps the only things they had in common were a conviction that the current system of music notation is inadequate and a determination that a new, user-friendly system will be in the works by the start of the next century.

Even when they disagree, the MNMA members encourage one another. They remind themselves of what they are up against, and one of their favorite images is that of David doing battle with Goliath. They are comrades-in-arms, joined in a common purpose, dedicated to a cause that for them seems almost a moral issue.

''My belief is that we are at a point, now, where we must take conscious steps to create a more humane music writing system,'' MNMA president Thomas S. Reed said in his closing remarks. ''And we must do what we can to institute it for all current musicians and all budding musicians. Having tasted the beauties of some of the newer notation systems, how in good conscience can we keep these matters secret?''

Reed is a piano tuner from Kirksville, Mo. He knew, he told me, that there must be others who shared his frustration with traditional music notation and who were independently developing solutions to what they perceived as the problems. Why not gather them together and form a united front? he wondered. So he placed notices in music magazines worldwide. More than 70 people from 20 countries responded to Reed's query. Working only through the mails, they organized themselves officially in 1986. Three years ago, in Norwich, England, they held their first international meeting. The proceedings of that conference have been published, and there are plans to publish as well the papers delivered at the St. Louis sessions. 

Interested parties can obtain copies by writing to the MNMA's headquarters at P.O. Box 241, Kirksville, Mo. 63501. What correspondents will receive is a bundle of articles that describe systems called Twinline Notation, Outline Notation, Chromatic 6-6 Notation, Trigram Notation, Mirror Notation, Klavarskribo, C-Symmetrical Semitone Notation, K-et-K Notation, Nomographic Notation, Panot, Equitone, Neo-Pente and several others that have yet to be fitted with colorful names. Most of them are based on the idea that, in music notation, what you see ought to be consistent with what you hear.

The pitch traditionally labeled C sounds like a C no matter what octave it is played in. So why, the modernization champions ask, do the written symbols for these pitches look so very different? The note for a low C hangs two notches under the bass staff, and the C an octave higher rests on the staff's second space; the next C can be written on a line placed above the bass staff or on a line placed below the treble staff; the next one goes in the treble staff's third space, and the next one goes two lines above the staff. Wouldn't it make more sense if all the Cs were notated more or less the same way?

And wouldn't it be easier if C-sharp, which is not at all the same as C, were written in a way that suggests its distinct identity?As it stands now, C-sharp is indicated by the note for C preceded by a set of hatchmarks that instructs the performer to play not C but rather the pitch a half-step higher. Why not give C-sharp the independence it deserves, ask the modernizers? There are 12 pitches in the chromatic scale, so why not have a notation system that has 12 discrete symbols?

These questions are posed by musicians who either have had trouble themselves in reading traditional notation or who have discovered, through teaching, that for many students the apparent ambiguities of traditional notation form an almost insurmountable obstacle. They are sensible questions, and they warrant a sensible response.

Music notation is a kind of writing that enables musicians to commit to paper a set of instructions that, when followed, will result in a reasonably accurate realization of specific musical ideas. And like any writing, it consists of arbitrary symbols that take on meaning only because they are assigned meaning.

In itself, a vertical line that bisects a shorter perpendicular line has nothing at all to do with a tongue pressed against the upper teeth in a speaker's mouth. But the letter ''T'' has come, over the years, to represent the sound that results when the speaker so positions his tongue and then pulls it back in a way that explosively releases a supply of air. Illiterate persons don't know this, and that's why printed material to them is indecipherable. The rest of us instantly translate the character into the sound, and we are able to imagine the sound without actually having to hear it. We can do this because long ago we were taught to do it, because in the years since kindergarten we have had lots and lots of practice.

The writing of ''T'' and all the other symbols in the world that stand for sounds or entire words was born of necessity. People spoke long before they wrote, and the ancestors of all of us for a long time got along just fine by simply talking to one another. But sooner or later there arose the need to preserve speech, to make otherwise ephemeral words somehow durable and communicable over long distances. With provinces to govern and poets to celebrate, the ancients invented writing. While they were at it, probably for the reasons that prompted their first experiments with verbal literacy, they invented systems of musical notation.

Archeologists know that music notation systems existed in China, India, Egypt and Sumeria as long ago as 2000 B.C. The notation system used almost universally today is considerably newer. It had its roots in Western Europe in the 7th or 8th century A.D., but it was not until much later - early in the 1300s - that it evolved to the point where it would be almost readable by a time-traveler from the present.

Western music notation began in the monasteries, where the only repertoire that warranted preserving was an increasingly large body of hymns and chants. Although the dutiful monks knew all the material by heart, they found it harder and harder to remember exactly which tune went with which words. So someone came up with a mnemonic device, a crude set of squiggles placed between the lines of text. The squiggles meant nothing more than here the notes go up and here they go down, but they were sufficient for the monks' needs.

A few centuries later, it might have been some young monk from Bavaria, just in from the hills and befuddled by all the chants he was supposed to learn overnight, who posed the obvious question: How much do the notes go up, and when they go down, how far do they descend? And it might have been his choirmaster, anxious for a good performance, who came up with an answer. All he did was draw a single horizontal line across the page and codify the squiggles into shapes that indicated a movement from the starting point of one, two or three pitches. But considering that this was still the Dark Ages, it was a brilliant idea, and it, too, sufficed.

And then, early in the 11th century, after the various notes of the scale had acquired their alphabetic nomenclature, an Italian monk named Guido of Arezzo drew three more lines across the page and started placing black spots either right on the lines or in the spaces between them. A spot on the bottom line meant a specific pitch, its precise sound - C or D or E, high or low or in between - determined by an upper case letter judiciously drawn at the left end of the staff. A spot in the space above the line meant the pitch one scale degree higher, and so on. Voila! - no more ambiguity.

Guido also came up with a plan that made it fairly easy for singers to understand how the notes - just from their appearance on the page - related to one another. He composed a hymn whose first phrase of verse begins on the first tone of the scale and whose subsequent phrases start on the successively higher tones. Guido said: Since the tune is so memorable, and since the initial syllables of the phrases are all different, let's use the syllables as names not for the pitches themselves but for the places they occupy in the musical scale. The Latin text of Guido's hymn goes like this: ''UT queant laxis, REsonare fibris, MIra gestorum, FAmuli tuorum, SAlve polluti, LAbii reatum.'' A more euphonious syllable eventually replaced ''ut'' as the starting point of the scale, but the others, with modifications, still survive. One of the more popular songs from ''The Sound of Music'' - the one that begins with the line ''Doe, a deer, a female deer'' - is a 20th-century takeoff on Guido's hymn.

After Guido, to make a long story short, music notation evolved as was necessary to accommodate the growing complexity of music the educated folk felt was worth writing down. Polyphonic music - music with two or more independent voices - did not happen significantly until the 12th century, and so it was only then that scribes began aligning separate staves in a way that foreshadowed the modern musical score.

In the 13th century, as the compass of melodies expanded, the staff sprouted a fifth line. Also in the 13th century, as tones in between the standard ones gradually entered the musical vocabulary, scribes prefixed notes with symbols that indicated a note should be sounded a half-step higher or lower than normal. In the 14th century, when rhythmic dance music and secular songs first came to be taken seriously, notes were fitted with stems and flags to indicate their proportional relationship to one another. But it all started, practically speaking, with Guido.

Organic as it has been, traditional music notation - especially as it concerns indications for pitches - dates back almost a millennium. In the cosmic scheme it may seem like a recent development, but in terms of Western civilization it is very old. It is too old, say the members of the MNMA. It is also too darned complicated, they argue with passion, largely for the reasons cited earlier. In response, they propose what seems like myriad solutions to their nagging bugaboos. As far as I can tell, the ''modern'' alternatives are based on some sort of logic, and a few of them - most notably the Klavarskribo method of notation for keyboard instruments that was launched 60 years ago in The Netherlands - have already generated a sizable amount of published music literature.

The ''modern'' systems, in one way or another, all fall short. Unless I really missed something at the conference and in the pile of conference proceedings I've been reading, none of them is so thorough or so flexible as the one instituted by Guido. It is hard for me to imagine that any of the ''modern'' notations could handle all of the tasks that the traditional system now so efficiently performs. And I find it troubling that, with few exceptions, the members of the MNMA seem not to realize this. Single-mindedness can be an asset to the creative individual. When it results in tunnel vision, however, it becomes a liability.

In this regard, I get the impression that the MNMA members are working with severe handicaps. They are able to see inconsistencies in traditional music notation, inconsistencies that were there from the beginning and which surely were obvious to Guido and his successors. What they fail to see is that these inconsistencies are no worse than those that bother most other forms of writing, and that within the system as a whole they are not inconsistent at all. Before one can read traditional music notation, it is necessary that one study it. This requires effort, to be sure, but the effort is no more taxing than that required to become literate in English or any other language based on a phonetic alphabet.

Whether developed in an ivory tower or a country cottage, most of the new notations proposed during the MNMA conference are practical only in limited ways; while they correct a particular problem or two, at the same time they create a thousand more problems that their champions apparently find unimportant. The few notations that are not limited, on the other hand, are for the most part so intricate that they can be deciphered - so it seems - only by a computer.

Although I am tempted, I will not say that any of the MNMA members I met last month is a genuine crackpot. I will say, though, that one of the group's chief characteristics - along with earnestness - is naiveté. One of the more poignant talks was titled ''We Cannot Expect Help From Anybody,'' and it included a diatribe against an international musical establishment that for various political, social and economic reason s is rigidly opposed to notational modernization of the sort the MNMA espouses.