If only he looked the part, Frankie Valli would have become one of the most important pop stars. No matter what "sound" has prevailed - the dumbfounding sound of Phil Spector, the ingratiating sound of The Beatles, the rustle of disco - Frankie Valli and The Four Seasons have assimilated just enough of the latest sound to engage the attention of the faddish public.

Although they are best known for "Rag Doil," "Walk Like a Man" and their big hits of the early '60s, Frankie Vallie and The Seasons have seldom gone a year without a best-selling single. When so many other groups were overwhelmed by The Beatles, "Can't Take My Eyes Off You" (Valli's first solo success), "Let's Hang On," a brash jazzing-up of "I've Got You Under My Skin" and a number of other singles, kept The Seasons afloat. In the '70s they have even managed to make their way through the desert of disco; in songs like "Who Loves You" and "Swear to God" they have wrung a littel life from a genre one assumed to be barren.

Despite his extraordinarily durable appeal as a recording star, lead-singer Frankie Valli remains little more than a voice. He has not achieved the "presence," the celebrity which many singers who are here today, gone tomorrow, enjoy today. This must be the reason Valli is finally striking out on his own as a solo performer, leaving The Seasons henceforward to fend for themselves. Diana Ross pulled it off. But she looks like a million bucks. Frankie Valli must lok pleasant enough off-stage; on-stage, singin in that helium driven falsetto of his, he looks funny.

You feel indecent just looking at him as he wrenches his face ready to hit the high notes. His face becomes the agonized face of a weightlifter jerking 300 pounds. his cheeks tighten around his nose, buttressing it, getting it ready. It's only through his nose that he can reach an upper register, but he sings through his nose as if it were an alto saxophone.

He never pipsqueaks very long. After each refrain he nose-fives into the rugged guttural voice in which he sings the verses.

It's too vad Vallis is famous for his falsetto. His normal voice is so strong, so matter-of-factly masculine, he has never had to affect the hoarseness and hysterics of the Tom Jones school. The urgency and credibility he can bring to the most makeshift lyrics has been matched by very few performers.

More often than not, thesongs Frankie Valli recorded in the early '60s serenaded some "Dawn" or "Sherry" or "Ronnie" from the other side of the tracks. While The Beach Boys were singing of the fun, fun, fun they were having with their T-Birds, surfboards, skateboards, The Four Seasons sang of teh ignominy they suffered as nobodies from new Jersey. Frankie Valli was forever worrying about becoming a "Big Man in Town": "Some day your folks will welcome me." It would be silly to imagine that the sing-song lyrics of the songs The Four Seasons made popular were ever meant to move anyone, to express anything, to achieve anything but rhyme. Their songwriters, Bob Crewe and B. Gaudio, wrote compelling songs, perfunctory lyrics.

And yet, as "The Four Seasons Story" (Private Stock Record PS 700.) makes clear, even the words of these songs are not entirely without charm. Nostalgia works wonders. Just as the giddiness of The Beach Boys delights many people who are nostalgic for more carefree times, so the hankerings of The Four Seasons for romance and respectability will touch those who are nostalgic for the days when marriage was taken for granted, and getting-ahead was what all good boys planned to do.

Frankie Valli may never have been a national celebrity of much import, but in his heyday he was Sinatra's successor as New Jersey's favorite son. His diction was the lazy, abrasive speech of the area. He looked like a million other boys from Jersey City, Rutherford, Hackensack. And the girls all loved him. The girls I knew, anyway. No schoolday passed without at least one girl in the class spotting one of The Seasons driving along Route 46, waiting in line at the drycleaner's, eating pizza at The Hot Grill.

Maybe these girls did see Frankie Valli bolting the toll-booth on The Parkway and maybe they didn't. The point is, California girls were no crazier for The Beach Boys than New Jersey girls were for The Four Seasons. Frankie and his buddies were simple, trustworthy fellows. They sang about the things that mattered: breaking-up ("Big Girls Don't Cry"); making-up again ("C'mon Marianne"); to do it or not to do it ("Save It for Me"). Grown up now, these girls will nevertheless be disappointed to hear that the gang is breaking up. The Seasons going one way, Frankie the other.

Of course, not all the music The Seasons made remains as exhilarating as it was when they were the only white boys as tight and vital as The Platters and The Coasters. But some of their music seems even more remarkable in retrospect. What other white group, then or now, could match their recording of "Stay"? And surely, "Workin' My Way Back to you" is the funkiest number four straights and a big band ever managed. Perhaps their most irresistible recording in one, from 1965 (only the Stones' "Satisfaction" outsold it), "Let's Hang On." One this record The Seasons are more than a hum, more than a doubling of Valli's lead. They pick up the melody, elaborate it, counterpointing Valli adroitly. It's hard to believe that he will sound nearly as good without them.