A violin, a viola, a cello, and many fourth graders

I have chosen three of the letters last year's fourth graders wrote the professional musicians after their week-long residency at the Greene Street Elementary School here. (No changes have been made in spelling.)

* ''Dear String Trio

''Thank you for comeing. I liked it when we made misic with phone numbers and words.

''from Mary P''

* ''Dear Ladies,

''I must thank you for teaching me to play two very classical instruments.

''I especially liked it when I played the cello on the last day. I also liked it when you had those two concerts and the piece by Bach.

''Yours truly,

''Zachary K''

* ''Dear Peggy, Corky and Barbara,

''I liked the song with the words 'Through the way where hope is guiding . . .' then we had a little music in the middle . . .'Hark! What peaceful music rings.'

''That was nice.

''I also liked it when we made thunder, lightning, and rain.

''I had a fun time. Too bad we couldn't learn to play a song on the violin. Goodbye, hope to see you again.

''Sicerely,

''Jason T''

Peggy James is a violinist, Cornelia (Corky) Watkins is a cellist, and Barbara Kunhardt is a violinist. They are professional musicians who both play and teach.

And through the good services of the Brattleboro Music Center they have spent several week-long residencies in public schools in this area.

I caught up with them the last week in January in the Greene Street School's fourth grades. The three ladies, as Zachary referred to them, are marvelously enthusiastic teachers. And they clearly work considerable magic in one week's time.

It is not unusual for children in the elementary grades to be exposed to a professional musician, but this is often a very brief affair. The musician may play for a bit, talk about the instrument, then play another bit, and go on his or her way to the next class or school.

What the music center has arranged (half the funding comes through a special state grant) in its residency program is very unusual indeed.

After an initial concert on a Monday, the three musicians go from room to room dividing the children into three working groups appropriately named Mozart, Beethoven, and Bach.

They bring with them several half-sized violins, and each child is taught some of the elementary lessons. By Friday, the day I was ''in residence,'' the holding positions weren't correct, finger positions were awkward, but each child who tried was able to produce a ''D'' then an ''A'' then a ''B'' on schedule for a piece dubbed ''The Lone Ranger.''

''Horses, horses, horses.'' And to ensure the correct rhythm, even the professional musicians bobbed up and down at the knees.

Some children were at the board pointing to the correct notes with rulers, others were conducting with pencils, some were humming along, and the music made by the children in concert with the resident string players was very, very good.

During the week's residency, the first lessons develop rhythm, next lessons get to notation, then on to interpretation.

At some time during the week, each student gets a chance to try the cello. And each one picks up some of the vocabulary, as evidenced by letting me know that they had composed their own ''Bach cantata.''

To help the children do some of their own composing, notes are assigned to the 10 digits. Then each child is asked to give his or her home telephone number, which is then translated into music. The student decides whether it will be played soft or loud, fast or slow, in deep tones, or high notes.

One fourth grader admitted to me: ''My phone number is boring.''

When the visiting trio asked the children in each class to direct them into making their instruments play together in such a way that they made a thunderstorm, it was remarkable to watch the youngsters' efforts to conceptualize in string music what they remembered from summer storms.

The patter of rain and the plucking of the viola and violin strings was never first; the cello's low tones are too much fun for that! No, orders went first to Corky to ''do deep ones, real slow and loud.''

Sometimes the children snapped their fingers to be rain and helped out the trio; sometimes they clapped for a similar effect. Another class produced some wind, but the final concert was the biggest treat of all.

One can imagine how very ''strange'' the Monday concert had sounded to many of the children unacquainted with classical chamber music. But by Friday they had learned enough to be enormously excited about hearing the ''familiar'' with new listening abilities.

During the final ''Bach cantata,'' a youngster joined Peggy on a borrowed violin, and six fourth-grade girls - all flute pupils - added specially written music, and the remainder of the children sang the chorus.

This listener thought it was lovely.

Those interested in knowing more about the work of the Brattleboro Music Center should write Catherine Stockman, 15 Walnut Street, Brattleboro, Vt. 05301 . The center runs a summer camp for young musicians, gives private instrument instruction, directs a chorus, provides school concerts, and so forth.