Springtime means more than robins, romance, and reading period. It marks the appearance of that most unusual phenomenon--the Boston Pops Orchestra. Season after season Arthur Fiedler and his men have been delighting highbrows, lowbrows, and no-brows with nightly renditions of the best in light classical and popular music.

But nobody spends a night at the Pops just to listen to music. The gardenia-scented lobby and transformed first floor (chairs and tables instead of conventional scats) bring to Symphony Hall an intimate, informal atmosphere which has been often copied but never duplicated. And when the music starts, competing against the incessant pop of champagne bottles and the gay chatter of the audience, there can be little doubt that the concert is nothing more than a musical party.

Opening night began with a loud and brassy treatment of Delibes' Procession of Bacchus from "Sylvia," and closed with a loud and brassy treatment of "Stars and Stripes Forever." In between, the orchestra played the usual Pops potpourri ranging from Tchaikovsky to Irving Berlin. The musicians, all members of the B.S.O., played well on the whole, with the exception of their rather lackadaisical reading of Komzak's "Girls of Baden" Waltz. The highlight of the program was Milhand's clever little Fantasy for piano and orchestra, with the young and brilliant Eugene List as soloist.

Arthur Fiedler (who looks more like an insurance salesman than a symphonic conductor) has lost none of his joviality. He conducted with briskness and precision and rewarded his audiences with encores whenever they clapped loud enough.

There are some people who don't like this kind of thing, just as there are some people who don't like Li'l Abner or corned beef and cabbage. Nevertheless, the Pops, by combining atmosphere with good music and low prices, has become--for better or for worse--a national institution. --lower case