Rock/Pop Paul McCartney: ''Pipes of Peace'' (Columbia QC 39149). I'll admit it, I've often thought Paul a bit oversweet. Exhibit A - his cloying ''Silly Love Songs'' from a few years back. Rock pundits have said this tendancy of McCartney's was tamed by John Lennon's darker visions during their Beatles era. Though McCartney has, if anything, grown more pop with the years in his musical composition, he has completely won me over with this LP. Perhaps the words from the song ''Sweetest Little Show'' were meant for McCartney himself. ''You've been around a long time/But you're still good for a while/And if they try to criticize you/Make them smile, make them smile.'' The title song, ''Pipes of Peace,'' delivers a familiar message - ''play the pipes of peace'' so the next generation will only sing songs of joy. Yet, instead of sounding shopworn as it should have , ''Pipes,'' dressed in McCartney's splendid music, sparkles. ''Say Say Say,'' the tune now being played into the ground on the radio, is a smooth, calculated cut aimed accurately at the ear of the pop fan. McCartney calls on reinforcements for this one, though - none other than Michael Jackson (who co-wrote the song with Paul). It's almost overkill, but the two together sound quite good. Though comparisons are facile - perhaps even painful in some ways now - I was struck by the flashback feeling ''Pipes of Peace'' and ''Average Person'' had. To the Beatles, that is. On the other hand, ''Keep Under Cover'' sounded like ELO. ''So Bad,'' the last cut on the first side (perhaps the only throwaway on the entire LP), was nonetheless notable for McCartney's amazing choirboy vocals. McCartney has brilliant pop music here. How could I have ever doubted him?