POP/ROCK Bob Seger & The Silver Bullet Band: ''The Distance.'' (Capitol Records. St 12254.) Bob Segar's music always sounds like hard work - not exactly the type of hard work the man from Motor Town did at the Ford assembly plant for three weeks when he was 18, though. No, it's more a feeling he's working hard intellectually and musically to produce sensitive rock ballads. Sometimes it seems as if he's working too hard. Of course, his favorite subjects - the freshness and pain of adolescence, the yearning to be elsewhere, the disappointments and anguish of love and adulthood - cut deep into the American consciousness. And Mr. Seger can sometimes strike a sensitive, perhaps even profound chord. ''The Distance,'' is made from the same mold of so much of his music. That, despite adjustments in the Silver Bullet Band and a heralded reversion toward harder rockers this time around. Nonetheless, there's an atmosphere, a charm, that breaks over the sometimes heavy-handed emotion of this LP. ''Roll Me Away,'' on the flip side, is an easy rocker that feels as good as the sensation of freedom it evokes. ''Shame on the Moon,'' perhaps the best song on this disc, has an easier sound and less overwrought vocals. By contrast, ''Makin' Thunderbirds,'' Seger's effort at profundity about working in an auto factory, wears thin quickly, despite the departure from the usual Segar sound with its nod toward classic early rock 'n' roll. ''Even Now,'' the first song, begins auspiciously but deteriorates into somewhat mechanical emotion and sound. Our major gripe with ''The Distance'' is that it fails to sound fresh, and that we're listening to these songs and these musical ideas for the first time. Needed is the type of freshness recognizable in ''Night Moves,'' a stunning song which Segar has admitted trying to out-write in the past.