As our distance from the '60s grows, it becomes easier to assess that period's music apart from the social convulsions surrounding it. As that reassessment goes on, it grows clearer that Brian Wilson's work may be far richer as pure music than anything the Beatles or almost anyone else produced. Behind the seemingly simple facades, all his songs contain intricate systems of melodic paths, rhythmic detours and harmonic intersections.

Brian Wilson is the prime creative force of the Beach Boys, which include his younger brothers, Dennis and Carl, his cousin Mike Love and his childhood neighbor Al Jardine. As Dennis once put it: "Brian Wilson is the Beach Boys. He is the band. We're his messengers."

When Wilson withdrew from the group's leadership at the turn of the decade, the band floundered artisically as well as commercially. Now that he has returned as producer and principal composer for last year's "The Beach Boys Love You" (Warner Brothers MSK 2258) and the brand new "M. I. U." (Brother/Reprise MSK 2268) Wilson has reasserted himself as a primary talent in pop music.

Wilson's songs have sold millions of records, but he has never been fully recognized as a major artist on a level with Bob Dylan and the Beatles. Yet Wilson contributed as much to the maturation of rock 'n' roll music as Dylan did to rock 'n' roll lyrics, and many of the Bealtes' musical "innovations" were done earlier and better by the Beach Boys.

By the 1965 "Summer Days (And Summer Nights)" Wilson had completely mastered the studio as an instrument. His use of unusual instrumentation and his puzzle assemblage of different tracks predated by a year similar "firsts" on the Beatles' "Revolver."

Far more important than his innovations were his use of harmony, rhythm and melody. From early in his career, he transcended the three-chord structure of most rock music and changed chords constantly, often making unorthodox switches or changing keys entirely. He transformed the familiar triads into major and diminished chords and into sixths, sevenths and ninths.

Yet Wilson was no mere tinkering craftsman. Unlike jazz or classical music, rock 'n' roll is more concerned wiht emotional impact than technical accomplishment. Having significantly expanded the musical colors at his disposal, Wilson used each to strike the precise emotional nuance he wanted.

Critics, though, find it easier to write about lyrics than music, and when rock 'n' roll turned very collegiate and self-serious in 1966, the Beach Boys became an easy target to reject as part of the frivolous adolescent past. Just as Wilson was recording his most ambitious music ever, he was considered passe.

Reportedly, the commercial failure of his late '60s music broke his heart, and he handed over leadership of the group to his brother Carl and contributed fewer and fewer songs to each album. He produced almost no music between 1973 and '75.

To much hoopla, he made his come-back with the 1976 "15 Big Ones," which was released unfinished and seriously flawed. His return to touring that year was not much better. To make matters worse, he made a disastrous appearance on NBC's "Saturday Night Live," where his deteriorated voice and persistent stage fright produced off-key songs and a zombie stare.

As a result, he and the group had been all but written off as contemporary artists when he made a real comback with last year's "The Beach Boys Love You." That comeback continues with "M. I. U." It's easily the best vocal harmony record of 1978.

Wilson works principally in two forms on this record: '50s rhythm 'n' blues and children's songs. For example "Wontcha Come Out Tonight" is a new song by Wilson, but squeezes several '50s styles into one song. It begins with a primitive doo-wop call-and-response, then turns to a seductive ballad melody, sung in one key by Carl, then in another key by Love. Meanwhile a high piano riff, a roaming electric bass and an emerging horn push against the ballad tempo. Finally the song breaks out in an R & B dance tempo with one set of vocals punching out the urgent invitation, "come out, come out tonight," another set of vocals drifting wistfully up into the higher octaves and a trumpet sliding in a third direction.

"Pitter Patter," the best of the children's songs, transcends nursery songs the way Tolkien's work transcends fairy tales. It's Wilson's most ambitious construction in a long time. The music imitates the different tempos of rainfall: The whole band pauses in midsong, then the lead vocal sweeps through like a wet wind, "Listen to the ra-a-a-a-i-i-n!" This semiltan-eously releases the window pane-beating percussion and the dripping syncopation of the harmony chants: "pitter patter, pitter patter."

Brian Wilson is once again creating intricate music beneath the catchy surface of Beach Boys' songs. Few people recognize all the subsurface activity in his earlier songs which sold well. Fewer are likely to find it in his current records which don't even sell that well. But rich music lies hidden in every period of his work and remains one of the underappreciated accomplishments of rock 'n' roll.