The operative slogan for the National Symphony's concert last night at the Kennedy Center should have been "Welcome to Miller Time"--Mitch Miller Time, that is--for the ageless musical messenger led the orchestra through an array of light classics, standards and folk songs.

Few artists have been as instrumental as Miller in exposing "good" music to the masses. If an audience has the time, he has the melodies, and there were plenty of memorable ones tapped during the program.

Using body English to conduct, and anecdotes to explain, Miller devoted the first half of the bill to pieces with pictorial associations, most notably, in the Intermezzo from Mascagni's "Cavalleria rusticana," which underscored the fight scenes in "Raging Bull."

In Fucik's colorful "March of the Gladiators," Miller the professor said, "one can practically smell the circus." One could practically hear the corn shuck in Pryor's "The Whistler and His Dog," as an uncredited dog bark topped off the tripping piccolo tune. The orchestra was in rare form, indeed.

After the intermission, the tone switched completely to the popular mode. Miller oversaw inspired presentations of "Tenderly," "As Time Goes By," and the twin lunar excursions, "Fly Me to the Moon" and "How High the Moon."

"12th Street Rag" came off spectacularly as a big, big band arrangement complete with clarinet and trumpet soloists standing for their spots, and the bass players twirling their instruments with choreographed precision.

The king of sing-along turned the spotlight on the audience for a potpourri of songs straight out of his 1960s musical variety show, "Sing Along with Mitch." Facing the crowd, his enthusiasm was contagious, for even the shyest of shower singers couldn't resist joining in.

Miller's expressive hand gestures, which once entered the homes of millions every week, functioned well as cue cards for the participants. If anyone has the whole musical world in his hands, it's Mitch Miller.