If "Roy Acuff . . . 50 Years the King of Country Music," had stuck to its subject, it would have been a 30-minute special, not the two-hour extravagance that appears on Channel 4 tonight at 9.

It's not that Acuff isn't a good subject; he is, in fact, one of the most interesting and important figures in country music's short history. But the show's producers have rejected the integrity of Acuff's career and saddled this retrospective with two dozen guest appearances that have precious little to do with Acuff or his music and everything to do with Nashville commercialism at its most crass. With hosannas and awards (including a taped message from President Ronald Reagan, fast becoming the electronic Western Union boy), it's too much like a roast without the humor.

The patriarchal Acuff, looking 30 years younger than his 78, still projects sincerity and enthusiasm. After 50 years in the business, he remains a seminal and much beloved figure, though he's well past his performing prime.

People such as Kenny Rogers, Dolly Parton and Barbara Mandrell appear on the show and gush adjectives without ever verbalizing Acuff's accomplishments or qualities. And when comedian Archie Campbell says, "I would rather have his word that anyone else's contract," one begins to sense Acuff's influence on more than music, yet there's no hint at the singer's deeply spiritual upbringing or how it affected his music publishing empire and defined his fabled business honesty.

There's also no sense of the impact Acuff had during World War II, when his music transcended its southern origins and kicked off the rise of country music as it's known today. All we get is the oft-repeated tale of the banzai slogan at Okinawa, "To hell with President Roosevelt, to hell with Roy Rogers and to hell with Roy Acuff."

When country moved uptown, forcing a change in Acuff's title from the original "King of the Hillbillies," it left its artifacts behind, trotting them out on the Opryland stage as brief reminders. "King of Country Music" offers precious little liberation.

Most of tonight's show has nothing to do with Acuff; they could have made do with any old singer.

The show's few good moments come in old clips from the eight Hollywood grade-B movies Acuff made in the '30s and '40s, exemplifying his down-home morality by refusing to be filmed shooting or drinking. An earlier clip of Acuff singing his biggest hit, "Great Speckled Bird," segues into his singing the second verse today; like a fine wine, he seems a tad better with age.

With two hours to fill, Acuff is also allowed to sing his other big hit, "Wabash Cannonball." Why not mention how he learned to imitate train whistles as a callboy on the L&N Railroad? Because then we couldn't hear a pop-country hit from Larry Gatlin or Crystal Gayle.

All in all, there's precious little history, insight or explanation in tonight's show. Viewers will wonder about this awkward, slightly embarrassed, elderly host. They'll never understand why a man who is at best a mediocre fiddler and who has never been more than a rough-hewn singer could have such a tremendous and lasting influence on a particular style of music. Now that's a story well worth telling.