This is the time of year when Arthur Fiedler used to play for his most important audiences. Not the affluent Bostonians and tourists who could sit at the tables during the indoor season of the Boston Pops and hear his music with an obbligato of popping champagne corks; but the thousands who would bring blankets, sandwiches, perhaps a bottle of wine, and sit under the trees on the green acres of the Charles River Esplanade.

He was not there, this year, for the Fourth of July Concert, and the "1812" Overture must have lacked some sparkle, even if the rockets shot up as vigorously as usual from their mid-river barge. Now, he is gone and Boston has lost its most notable landmark since Scollay Square.

Fiedler began conducting his outdoor concerts a few months before the Depression hit -- in the year I was born. It was not until a few years later that I discovered the free, outdoor concerts in July, only a nickel subway ride away from home. (You could still swim in the Charles River then, a short walk away from the Hatch Memorial Shell where Fiedler and his orchestra worked their magic).

In the '40s, teen-agers would go in little, festive groups. If you arrived late, or wanted to be under the trees, you found yourself hundreds of yards away from the podium. But even at that distance, Fiedler was enormously impressive -- a stately, white-haired figure whose smallest gesture evoked waves of glorious sound, and the instruments behind him glittered like the music they were playing.

You could munch a sandwich as you listened, or exchange remarks (but only in whispers) during the music -- even get up and stroll (careful of the bodies spread out on blankets) for a closer look at the genial smile, the white moustache that became a sort of trademark. For all the informality, there was a kind of electricity running through the crowd. The ages ranged from infants to octogenarians.But while the music was playing, even the oldest were kids again for a while, even the poorest were temporarily rich.

Once touched by this enthusiasm, which I shared with thousands during those warm nights, the symptoms rapidly became intense. When the short summer season was over, we would turn compulsively to the radio listings -- some of us feverishly hoping that the Fiedler broadcasts (blessedly frequent in Boston) would not be preempted by such adult fare as Lowell Thomas or Amos and Andy.

Finally, the dependence on summer and the radio dial ended with the arrival of a (second-hand) record player, an awesome triumph of technology that would produce instant Fiedler (or Frank Sinatra or Benny Goodman) at the cost of a few turns of the wind-up crank and the occasional replacement of a needle.

The fact that Fiedler shared out 78rpm turntable with Sinatra was symptomatic of one of his problems.

To minds of a certain noble simplicity, there is "good" music and there is "popular" music, and never the twain shall harmonize. When Fiedler became widely and enthusiastically identified with one, he was automatically banished from the other. This despite the fact that he made pioneer recordings in many corners of the classical repertoire -- for example, Corelli and Telemann long before baroque music became popular.

In fact, the first notes of Stravinsky I ever heard were conducted by Arthur Fiedler with the Pops.

It would be splendid, no doubt, if all of us were born full-grown like the goddess Minerva, instinctively loving Bach's "Well-Tempered Clavier" and Beethoven's Quartet in C-sharp minor. But we crawl before we can walk or run.

Arthur Fiedler caught most of his audience at the entry level of classical music, nourishing their taste not only with Gershwin and Leroy Anderson, Sondheim and Mancini and the Beatles, but with substantial classics (there was always a concerto as the centerpiece of his programs) and with the enormous repertoire of light classics. The top-40 items did not come until the final section of the concert, as a rule, and they were played with the same skill that was dedicated to Beethoven, Bach or Brahms earlier in the evening.

In boston today, Fiedler's legacy can be seen not only in the affluence of the Boston Symphony, the parent organization of the Pops, but in a climate hospitable to music of all kinds. That city's musical life being what it is, a large part of the enthusiastic and varied audiences must first have encountered serious music, as I did, live and in person, sitting on the grass of the Esplanade and listening to Arthur Fiedler.

At least one of those beneficaries warmly returned the favor during the 1960s: When Sarah Caldwell invited Fiedler to conduct her production of "die Fledermaus," the marquee proudly proclaimed that the opera was "Die Fiedlermaus," and thousands of Bostonians were willing to sell their souls for tickets. The liquor laws being what they were, we sipped orange juice rather than champagne during the intermission, but it was still a glorious event.

In that experience, and in dozens of others before I had ever thought of writing about music, Arthur Fiedler taught me the uncomplicated but essential lessons that millions of fans also learned: That music, before all else, is and should be a joyful experience, and that any piece of music, no matter how simple, deserves the best performance one can give it. CAPTION: Picture 1, no caption; Picture 2, Arthur Fiedler after his 50th anniverasry concert in May, by UPI