Late last week Beatrice Judge's 28 fourth grade students at the John Eaton School here became the first of what may be many thousands of classes to view PBS's pioneering new experiment in television education called "Music."

Tonight, the public will get its first sample of this new approach - in 10, 30-minute installments - to teaching rhythm, melody, harmony tone color, dynamics and the rest at 7:30 p.m. on channels 26 and 53. The series principal impact is intended however, in the classroom, not the living room.

"Music" borrows visual techniques from a wide range of sources - "Sesame Street" to the game shows. And in musicial materials at one point embraces within about a minute fragments of motown the Beethoven 9th a chuggin train engine, bluegrass, Stravinsky's "Firebird" and a folk song.

Instead of Big Bird and the Cookie Monster, we have "Bernie the stage manager," a gorilla, a frog and "the Melody Doctor," played Groucho-style by conductor Murry Sidlin, who who emgees the entire series with great elan and a fine rapport with children.

"Music" is an innovative new educational tool produced by WETA with federal support, designed to help fill a growing music education void in the public schools, particularly at the intermediate level.

Music has never, had a very high place in the American curriculum as an exhaustive report documented last spring. And this condition has been aggravated by increasing budgetary pressures on school systems with declining enrollments and increased costs: something has to go, and because many regard music as a frill, those teachers are among the first to go. Nineteen out of the District's 70 clementary school vocal teachers were cut only last month. And John Eaton's Home and School Assn. pays its music teacher out of private funds.

The upshot is that in many places music either will not be taught at all at certain levels, or it must be done by the regular classroom teacher, who more often than not lacks expertise."

It is for this situation that "Music" with its video installments and its 64-page instruction guide (for even "the tone-deaf teacher, as one sponsor said), is designed.

The utimate test of such an endeavor is the children's response. And I trust the reactions of those at John Eaton last week far more than I do my own. They saw the show on rhythm (number 2) and the one-hour class was without doubt successful. Admittedly the conditions were exceptional. A video-cassette machine was brought from the studio. And the teacher was Sidlin, former resident conductor of the National Symphony and now head of the New Haven Symphony. The rhythm program, also, is one of the best ones, with a particularly funny, illuminating sequence in which phrases of "I Got Rhythm" are sung alternately with and without rhythm.

After the showing, Sidlin quizzed the students with the question, "What is rhythm?" Here are some of the answers: "Getting the feel of music:" "a beat;" "it adds something;" "music's assistant." Not bad, all the adults agreed.

The music critic or the television critic could thoroughly nit pick details of the shows. Tonights, for example, is a little too general. The symphonic interludes, recorded in three days with the National Symphony, are not the polished performances you would get from, say, the New York Philharmonic Young Persons Concerts. But the "Music" series serves a different audience and purpose. And aside from those, the Office of Education knows of no other sustained music-education undertaking on television.

The key to the "Music" series' impact is the extent to which it is used. PBS reaches only about 50 per cent of the country, but it reaches far mre, than that percentage of classrooms. Schools may use the visual segments three different ways: through video cassettes loaned by the PBS outlets (assuming the school system has a cassette machine): through monitoring the series on TV sets when it is rebroadcast during school hours, starting Jan. 3; through having students monitor the series on home screens, to be followed by classroom sessions on the installments.

PBS outlets are being urged in vigorously promote "Music," and WETA says it has been sending out teacher's guides at the rate of about 100 a day for the last two weeks. Libraries also are participating.

The preview at John Eaton has stirred such enthusiasm thre that its principal, Patricia Greer, has decided to show the January television rerun to all 4th, 5th and 6th graders. The explained, "The children are absolutely fascinated."