CALL IT TRADITION, nostalgia, continuity or corn, but just as our musical thoughts have always turned at Christmastime to Bing Crosby, who died last month, we have never really considered New Year's Eve official without Guy Lombardo, who died Saturday at the age of 75. The midnight ritual of the networks would begin with the hold-on-to-your-hats, play-by-predictable-play coverage of Times Square by veteran radio announcer Ben Grauer, who also will be missing for the first time this year; then dials worldwide would flick to the broadcast from New York City's Roosevelt Hotel Grill and in later years to the Grand Ballroom of the Waldorf-Astoria for the purring-saxophone rendition of "Auld Lang Syne" by the famed Royal Canadians.

Sure, the horns, hats, balloons and streamers were silly, but who cared? The musical enjoyment that the Lombardo silken sounds brought to countless millions of us was genuine - and if you weren't out there dancing, you hummed along. "The wonderful part of my job," said Guy Albert Lombardo Jr. only a few years ago, "is that I only see people when they are happy." And for the last 50 years - ever since his first network radio broadcast over the Columbia Broadcasting System - he, too, was happy, never losing a boyish exuberance that invigorated the many longtime members of his orchestra.

While New Year's Eve was the big night for his music, it was but a small part of the grueling, on-the-road schedule on which Guy Lombardo thrived even in recent years. The band has worked as many as 47 seven-night weeks and clocked some 60,000 miles in a year. And whether it was in the ballrooms, theaters, campuses or over the airwaves, that unmistakable ricky-ticky beat and the distinctive arrangements endured through the musical transitions from swing to jam, jive, boogie-woogie, mambo, behop and rock. Moreover, the sounds of "Lombardoland" were to influence the musical styles of many of the big dance bands that became famous in the 1930s.

Some of use would chuckle at the way the Lombardo orchestra could adapt almost any number to its style, for the Royal Canadians could make the score of "Fiddler on the Roof" sound like "Gimme a Little Kiss, Willya, Hon?" or "Boo Hoo." Still, as the slick-haired, tuxedoed band leader said, "Anytime a band has a 'class' following, anytime it creates a distinctive quality, some of the other musicians call it corny. What's bad about that? A band doesn't have to start worrying until the customers complain."

And we can rest assured that in a little more than seven weeks, when people gather to usher in 1978, that familiar sound will be heard from coast to coast - the "sweetest music" anywhere.